Cooking is one of the many meeting grounds of science, art, and culture. I don’t believe you have to pay much attention to science to be a great cook, but if you want to understand more about the how and why of food preparation, science can help. When working with plants and plant products, there are some particular times at which the science is so relevant that any cook would be amused.
Major points to be conveyed….
- Plants are truly “raw” materials. Much of food preparation relates to harvest, storage, processing, and preparation methods that will preserve the qualities we want from the materials.
- Preserving fruits and vegetables is artful chemistry.
- Cooking that involves plants and plant products responds to temperature-specific points of conversion and teaches us much about miscibilities and emulsions of polar and non-polar materials.
Elements of scientific context surface in discussions I have with students about plants, food, and cooking, particularly in three areas: preparation of fruit and vegetables, breadmaking, and candymaking. In this section, we will talk through the activities and major points generated through those encounters.
Between Farm and Table – the Botany of Food Prep.
When talking with people about vegetables and fruit, we have to cover some of the same information that surfaced in Botany for Gardeners, but for different purposes. Consequently, in this unit I am not as concerned about which part of a plant is being harvested, rather the focus is on how the nature of plants impacts food handling techniques.
When going through this discussion with students, I like to provide countertop hotplates (preferably induction units with shallow pans), cutting boards and knives, baking soda and vinegar, and dissection microscopes. You can work with many different kinds of produce, but certain materials are suggested in the discussion.
Discussion: When plants are harvested and brought to the pantry, changes are already in gear. Home gardeners, of course, bring their produce to a place where it can be washed, dried, and if necessary, refrigerated. In commercial agriculture, things are not so easy and great effort is given to managing changes that can occur at this time.
If you have ever visited a fresh produce field during harvest, you will know that warm produce piled in bins does not fare well. It has to be cooled quickly to slow degradation. That can be done in many ways (see North Carolina State University course notes, AG 414.1 WWW at the website www.bae.ncsu.edu), but one simple and interesting method for high end perishable crops is to load produce boxes in a trailer that is moved to a chamber where a vacuum is applied. Evacuation removes surface liquid, quickly lowering temperatures through evaporative cooling.
Regardless as to scale or method, controlling post-harvest temperature is important because these products are still alive. The tomatoes and pumpkins, lettuce and celery – even onions and potatoes – are as alive on the truck and in the market as they were in field. That means biochemical reactions continue. Most people know the story of sweet corn, special strains of corn that produce high quantities of sugar in the maturing grains.
The moment an ear is cut away from the parent plant, though, enzymes begin assembling free sugars into starches – which are plant storage products. The sweetness of the kernels drops quickly and to aficionados, the quality plummets (personally, I like field corn that is not so sweet).
Corn is extreme in this regard, and a good reminder that change continues. But slowing undesirable chemical change is just one of many reasons for lowering the temperature. Another reason for lowering temperature is to reduce water loss, which is especially damaging for leafy produce. To protect both quality and market value, green grocers chill and use mist to help maintain freshness.
Added processing helps with many crops, especially fruit such as cucumbers and root vegetables like carrots. We enjoy seeing handsome carrot foliage, which reminds us that products like carrots and beets are fresh, but the challenge for the grocer is that water loss from foliage will quickly cause roots to shrivel. This is the reason it is fairly standard practice for store clerks to wrench foliage off of the carrots while bagging, so customers will not be annoyed at the resulting shriveled roots.
Once in the home kitchen, life span is yet more limited. Keeping produce in plastic bags or containers will conserve moisture, but even chilling may not halt other changes. Many leafy vegetables, such as turnips and parsley, have a short
shelf life, their leaves yellowing quickly. Even more durable produce like green beans continue to change. And of course there are the secondary issues of fungal and bacterial contamination, which usually thrive in moist conditions.
People who freeze and preserve their own produce have many methods to halt degradation. I recall days as a teenage gardener, blanching (dipping briefly in boiling water in order to stop the clock) quarts of peas and beans before packaging for the freezer. Commercially, of course, processors have the capacity to flash freeze vegetables, sometimes eliminating this stage. But home economists learned that a normal home freezer might not chill quickly enough, or cold enough, to halt enzymatic maturation and breakdown. Blanching does that trick. And blanching has another very curious effect – actually brightening the green color of many vegetables. Today I understand this instant greening says nothing about freshness or quality – it results from a quick breakdown of tissue that eliminates air pockets in foliage and green fruit. Filling the tissue with water intensifies color through cutting down light scattering that is caused by pockets of air in living tissue.
But we consume many vegetables raw – completely fresh and unprocessed. Celery sticks, though sliced to uniform lengths, are still very much alive when we bite down. Onion slices and even the diced prepared onion you can purchase in bags are made of living cells – as is the garlic you have cleaned to push through the press. It isn’t as though these products have much potential to survive, but if the cells were no longer alive (and if they had not been prepared through drying, pickling,
fermenting, candying, or cooking), they would not be desirable.
Prove this to yourself. Cut up a small onion. Place some in a container in the refrigerator and freeze the remainder. A day later, bring both out and let them come to room temperature. Ice crystals that formed in the frozen onion will have destroyed most of the cells, which are not going to have the same qualities as the still-fresh tissue.
This is true for frozen carrots, peas, and those other colorful flecks in veg-all-like products. We have become accustomed to using frozen mixed vegetables to assemble soups, but these convenience products are not exactly the same as fresh; they can’t be. Frozen products have to be used quickly once removed from the freezer, because the cell structure is compromised, and further deterioration will be yet more rapid.
Pre-cooked, canned products are also dead – but even more so. Not only are membranes destroyed and cells disrupted, the pectins that help hold cells together are cooked and tissues have become mushy – so further stewing will not improve their condition. In any regard, once you open cans of vegetables or thaw frozen veggies, they are perfect media for microbial growth – which means they should be used immediately, for they degrade rapidly. And there are precious few foods we consume in a slimy, rotten state.
Four Basic Processes for Plant Foodstuffs: If produce is not to be consumed while totally fresh and raw, what are we accomplishing through preparation? Basically, there are just four general ways to deal with plant material. We can:
- Dry at air temperature, use modest heat to dehydrate, or freeze-dry. This takes the water out of cells, which usually kills them and stops most processes, but it does not raise temperature enough to alter chemical composition significantly. Note that most seed are normally dry; without additional processing they are alive andwell.
- Chop, grind, abrade, or pulverize it, destroying some or nearly all cell structure. This will kill plant cells at varying levels, but not sterilize the material or halt chemical reactions. Indeed, pulverizing exposes more constituents and surface area to enzymatic activity and decayingorganisms.
- Apply temperature, either freezing or cooking plants through boiling, baking, and frying. Freezing kills cells through creation of ice crystals, but does not necessarily sterilizethe product. Cooking kills cells, stops process, and can even sterilize. But cooking also denatures proteins, gelatinizes starches and pectins, and homogenizestextures.
- Prepare, ferment, or fix plants through denaturing with chemicals like vinegar or alcohol, dehydrating them with salts and oils, and decomposing them with lye and other caustic treatments. Chemical treatments break down cell membranes and even other structural components. Many also act as preservatives by creating circumstances in which destructive bacteria and fungi cannot thrive.
Those basic activities are not discrete, especially when it comes to Processing and Preserving. Home and industrial procedures typically combine elements of those basic processes, such as in:
Fermenting: Using microbes to break down sugars and starches into gases, acids, and alcohols. Principal uses with plant products include production of breads, alcoholic beverages, soy-based products (often in brine), and cacao seed for roasting. Fermentation does not play a significant role in tea production, even though vendors will use the term.
Oxidizing:Bruising or macerating plant material in order to expose potential flavor components to various enzymes and fresh air yields compounds that become “oxidized” – taking on new color ad flavor profiles. Such procedures play a significant role in producing teas, though steaming, smoking, flavoring, and drying are involved variously to create different kinds of teas. Some teas even involve fermenting in early stages.
Nixtamalizing: The hard fruit wall of dry corn kernels is the annoying component of popcorn, the plastic-textured shells that hang out in the bottom of the bag. For hominy and processed masa (to make tortillas or tamales), that fruit wall is removed through boiling kernels in very alkaline water (lye water, historically made from wood ash). Not only is the fruit wall removed, but calcium in the water alters the endosperm proteins so as to yield a dough (a masa). [search nixtamalization in the WWW]
Salting and Brining: Salt is the simplest compound available for changing water content of tissue. By crusting tissue in salt, water will move out of the tissue into a solution with the salt. By infusing salt into tissue, the tissue will hold moisture (and it will, of course, taste salty). Salted products, such as caper buds, are protected against putrefaction because microbes will not survive in the such highly concentrated media.
Coagulating:Tofu production involves processes similar to those employed in cheesemaking. Liquid made from soybeans is a white milk, filled with suspended proteins Using salts and enzymes, those can be coagulated to a curd for further production.
Pickling: Saturating plant tissue with acids, like vinegar, retards growth of certain toxic bacteria, such as Clostridium botulinum, the microbe responsible for botulism. I stay away from anyone’s home-canned green beans, but have not so thoroughly feared home-cannedtomatoes.
Sulfuring: Apples and stone fruit, which are popular and useful as dried fruit, are often sulfured because the sulfur blocks changes in natural compounds that discolor the dried product.
Candying and sugaring: Similar to brining, candying infuses plant tissue with sugar at such concentrations as to prevent growth of bacteria (when the fruit is kept dry) Since candying involves heating at high temperatures there is often a component of sterilization involved.
Sugaring compares to salting, with water moving from tissue into the surrounding sugar. Many fruit (dates, persimmons) might be sufficiently high in natural sugars as to self-preserve.
Leaching: Oddly, many important food plants are toxic when raw. Taro stem (it’s not a root) and certain kinds of Cassava (manihot, yuca, tapioca) may not be safe to eat until toxic compounds have been leached from the tissue.
Blanching: Perhaps the most common use for blanching is to ready tissue for cold storage, in that a quick dip in hot water will halt enzymatic reactions without significantly cooking or altering the tissue. A more earnest form of blanching involves boiling products like black-eyed peas in order to leach complex sugars (oligosaccharides) that promote flatulence.
Sweltering: In some instances, particularly with tea processing, and manufacture of vanilla flavoring, the principal treatment involves sweltering – storing material in a heap or in containers to encourage some initial breakdown.
Roasting: Many plant products are roasted before being stored and used. In most cases, roasting develops desirable flavor and aroma, as with coffee and cacao. In some, roasting denatures toxic substances, as is the case with cashews. In many cases, roasting prolongs shelf life also (as with wheat germ) or readies the product for further cooking.
Smoking: Perhaps more associated with meats, smoking is used for some plant material. Lapsang souchang tea is dried over smoking pine needles.
Flavoring: Herbs, spices, flowers, and essential oils are used to flavor many products. Generally, these compounds do not aid in preservation, though they may be crucial to create a suitable flavor profile as pure adulterations, extracts, or part ofmarinades.
Milling: Generating flours, meals, and other cereal products through mechanical grinding and sorting In the end, however, we still have the four basic processes, and need to think about how they relate to plants and plant biology In each we have choices as to what taste, texture, preservation, and nutritional value to prioritize. Let’s talk and test our way through advantages and issues of these treatments with different kinds of food plants.
Drying and Dehydrating: Numerous products we purchase are simply dried, herbs and spices especially. When gently dried, plants lose water (which can constitute as much as 90% of the fresh weight) but may retain much of their color, especially when stored properly. The water in cellular vacuoles regulates crispness, but water permeates plant tissues. Without water there is no life in a plant, thus thorough drying of leaves and fruit kills tissue (except in most seed, which are usually viable when dried normally.) But essential oils, sugars, proteins, etc. remain reasonably stable. Indeed, drying concentrates many essences and compacts more plant material in the same volume, which are the reasons recipes will often suggest using a lesser quantity of dried than fresh herbs.
Other than aroma and flavor, there is absolute difference in texture between fresh and dried material. Dehydrated cells can be rehydrated and cellulose walls remain, but pectins, sugars, and starches are no longer in the same relationships in and around intact cells. You may get a wonderful product, but it cannot be the same product as when using fresh material. Onion flakes, for example, give flavor, but you will not coax the same caramelized, gelatinous product from them as we achieve with fresh onion.
Dehydrated potatoes are renegades in this regard. Drying may disrupt cells, but does not destroy the starch plastids. As long as you lubricate dehydrated potatoes with plenty of butter and do not overcook or over-whip the pulp (just as with fresh potatoes), the starch plastids rehydrate fairly well and will not become so gelatinous and sticky as to make a paste. Dehydration actually increases the firmness of grated potato in commercial hashbrowns (and those boxed au gratin chips).
Once cooked, the tiny rehydrated potato strips that brown in layers on café griddles have a denser, firmer texture than you could ever coax from fresh-grated potato at home because café potatoes often arrive in bags and boxes, as dehydrated strips. Even rehydrated and cooked, these suckers do not break down You can confirm this by boiling two small mounds of potato in the induction pan – one being freshly-grated potato and the other a bit of the rehydrated strips. Those cell walls will never re- inflate around intact cells – the rehydrated strips cook up more like pasta as compared to the crumbly texture of cooked potato.
Of course drying fruit is ultimately useful concentration. Not only is flavor more intense, but sugar concentration rises to the point of preserving tissue against bacterial and fungal activity. This is possible because most contaminating organisms cannot survive in such high concentrations of sugar (the same is true with salt); the concentrated fruit would pull moisture out of an invader – rendering it lifeless. A popular Japanese technique for preserving certain Persimmon cultivars is to air-dry peeled fruit, allowing moisture to evaporate while sugar exudes and crystallizes on the outside, creating a densely pulpy-sweet, sugar-encrusted treat.
Tea (Camellia sinensis) is an important dried product. But the freshly-picked leaves and growing tips undergo various processes. Bright green teas (especially macha) are picked, usually lightly steamed or flamed to stop enzymatic reaction, and quickly dried, all of this being accomplished gently enough to preserve the green color. Most other teas are dried after having been rolled, bruised or mashed and allowed to moulder for a bit (unfortunately, producers call this “fermentation”), during which time oxidation and other organic reactions develop new flavors. Teas can be also be dried using smoke, which produces yet additional tastes.
Cutting and macerating physically destroys cells to varying degrees. From personal experience, we know we arebursting cells because cutting an onion ejects chemicals that quickly bring us to tears. Otherwise, onions seem to bear up to this brutalization fairly well. Cut onions do not discolor quickly or deteriorate.
Not so for potatoes and apples. Both begin to darken immediately, a browning process that can be retarded by dowsing the flesh in water, treating with acidic juice or liquid, or by sealing the cut material in a vacuum bag. With cutting, clear compounds previously stashed away in each cell’s vacuole turn dark when mixed with certain enzymes and exposed to oxygen (chemically, they are oxidized). Washing fresh-cut apples and potatoes removes the offending chemicals; leaving them in water helps keep away theoxygen.
We can also inhibit the browning reaction by treating cut surfaces with lemon juice – which is sour with the antioxidant ascorbic acid. Industrially, apple slices and other fruits are often sulfured, which retards browning by blocking the reaction. Some vegetables, such as cut lettuce, can be briefly blanched to denature the enzymes that promote browning. Of course, cutting lettuce used to be discouraged. Instead, we were admonished to tear lettuce for salads. Tearing destroys fewer cells, thus keeping the leaves a bit crisper and limiting browning. But let us face it, not many people have the time and patience to hand tear all of those leaves.
Temperature is everything when it comes to food preparation with plants (check out the discussion of Temperature in the Reader, Chapter 10, Hands-On, Section 1, Techniques). Here, of course, we confront that unfortunate issue of ºF and ºC. Only in the US and a few smaller countries do people still regard 32º as the temperature at which water freezes and 212º as the boiling point. In 1724, when the Fahrenheit scale was devised, the range of 0º to 212º was initially standardized based on devising convenient gradations between icy brine, freezing water, body temperature, and the boiling point. The simpler to use and understand centigrade scale (ºCelsius) reigns through the remainder of the world. What a disaster for American science, in that children learn to think technically in the archaic, awkward, and meaningless Fahrenheit framework. What’s more fascinating, our own Linnaeus is credited with formalizing the current centigrade system in 1744, when he decided to reverse Celsius’s numbering – designating 0º as the freezing point and 100º for boiling water (the Swedish astronomer Anders Celsius, who created the centigrade thermometer, had numbered boiling water 0º).
But even with our allegiance to Linnaeus, and the fact that every research lab in the US works in the metric system (including using the centigrade scale), we are stuck in the past for food, weather, and architecture. In this discussion, I will use both systems.
Let’s start below freezing. Freezing kills most fresh plant tissue, because ice crystals form that destroy cells. (Note this is not the case for many grains and other kind of seed, which are well adapted to surviving freezing conditions.) Commercially, an ideal temperature for quickly freezing and storing foods would be that one point at which the two scales cross (-40 ºC, which is the same as -40 ºF). Even though frozen at this temperature, some organic reactions will continue. This means that for longterm freezer storage, produce benefits from blanching – which denatures enzymes and halts many other changes. Most home freezers hang out at -20 ºC (which is -4 ºF), making long term storage yet more problematic.
You can push the temperature lower, of course. Some restaurants play with liquid nitrogen (-196 ºC or -321 ºF). At this incredibly low temperature, tissue freezes rock hard instantly, becoming so cold that no organic reactions occur and storage is indefinite – so hard that you can do fun things, like shatter a banana or lettuce leaf into powder.
You should not consider doing this, at home or for a demonstration, even if somehow you have access to liquid nitrogen. Though entertaining, liquid nitrogen is hazardous amusement. One accident, and someone could lose a finger – presto digito. At the Gardens, we work with liquid nitrogen to cryopreserve plant tissue for conservation, and have to attend to many protocols – including detection and venting to ensure nitrogen does not leak into surrounding air and suffocate people.
Storage Temperatures: Going the other direction, above freezing, we pass through storage temperatures. Quoting Harold McGee: “The most effective way to prolong the storage life of fresh produce is to control its temperature.” McGee reminds us that keeping temperature just a few degrees below normal room temperature helps maintain freshness. But the most appropriate storage temperature varies with the material. As lowland tropical fruit, bananas do not enjoy standard refrigeration; their skins turn brown. Tropical fruit generally benefits from being kept cool, but probably around 10 ºC (50 ºF) or higher. Garden vegetables can take cooler temperatures. In fact, if you check out www.FDA.gov, you will find Recommendations to Food Services and Retail Food Stores that (based on the 2009 Food Code) require fresh leafy vegetables be kept at 5 ºC (41 ºF) or cooler, to lessen the chance of bacterial growth. Since freezing will destroy leafy vegetables, it seems to me you want leafy vegetables to hang out at just a few degrees above freezing. Apples are usually stored even colder, at near freezing. In both instances, packaging that limits available oxygen will also help slow degradation.
But packaging is critical for another reason. Refrigerators create dry atmospheres. You have to package vegetables (even fruit) so as to protect them from moisture loss. You are welcome to conduct trials on your own, but my experience has been that enclosure is necessary.
By the time food gets to body temperature (37 ºC or 98.6 ºF), some plant products will be affected, particularly products heavy in fats and oils. Specifically, I am thinking about chocolate, the manipulation of which requires a full suite of knowledge and skills. Cutting to the chase, chocolate is nicest when the complex fatty mixture sets with a specific crystallization pattern. Unfortunately, there are at least six possible forms (I-VI), and the most desirable for consumption (form V) is not the most stable (which is form VI).
By melting chocolate at 50 ºC (to eliminate crystalline structure thoroughly), cooling to 22 ºC, then reheating to the point it is just barely molten (31 ºC), manufacturers can select a solution that will set with the right crystalline form. This is called tempering. Ill-tempered chocolate does not behave and does not have a nice texture.
In home cooking, people take a short-cut and “seed” molten chocolate with a bit of nice (form V) chocolate, which preconditions the molten chocolate to set in that desirable form. If you need to dip or coat something in a small amount of beautifully-tempered chocolate, you can also gently melt chocolate that is already well-tempered to use for coating Unless you mistreated it, the “couverture” should remain tempered when it sets.
The purpose of this bit of chemistry is not to teach chocolate tempering, but to explain that the temperature at which chocolate is stored is important. If you purchase expensive chocolate and discover it is not a handsome, lustrous rich brown and crisp, it was mishandled.
Experts suggest storage at 15-18 ºC – which in American homes corresponds to 59-64 ºF. At higher temperatures, chocolate reverts to other forms, and weird things happen. It may be okay for cooking, but not for eating. The texture of mistreated chocolate may be grainy, and the surface may have turned white (which is called “bloom”). You can usually melt chocolate and restore its color and temper, but that is a bit of a trick because the temperatures must be meticulously gauged.
It is not all about chocolate. Storage temperature, exposure to oxygen, and even exposure to light can impact the quality of any plant oils, some more seriously than others. And oil-rich products, such as whole grain cereals will suffer over time.
One of the most infamous is wheat germ, which goes rancid rapidly once exposed to the atmosphere. Even refrigerated wheat germ has a relatively short shelf-life. Certainly, with all oil rich products (wheat germ, seed), storage in sealed containers (vacuum-packed is even better), at cool to freezing conditions will prolong quality.
Cooking: Once plant material is heated to as much as 60 ºC (140 ºF), serious things begin to happen. Cells start to rupture and internal cell structure begins to collapse, so color will change as chlorophyll and its surrounding connections break down. Color change is exacerbated with increased acidity, which is the reason a bit of baking soda will help maintain green color in vegetables (though it also promotes cell breakdown, and therefore mushiness). Before we understood harmful effects of metals, cooks favored raw copper pots, not just for the beauties of their heat conducting capacities, but because the metal ions released from the copper pot help preserve chlorophyll structure and color.
Boiling of water is directly dependent on air pressure. At higher altitudes wa-ter boils at lower temperatures. According to Wikipedia, at 10,000 ft altitude, water boils at 93 ºC (201 ºF) while on Mt. Everest, water would boil at 70 ºC (158 ºF). A cook on Mt. Everest would need a pressure cooker to make boiling water there have the same impact as boiling water does at sea level.
As cooking temperature rises to the boiling point, the pectins and hemicelluloses that help hold cells together begin to gelatinize and dissolve. Once again, this chemical change is impacted both by pH and water hardness. More acid liquids (and harder water) help preserve texture, while alkaline conditions (and addition of salt) promote dissolution of the compounds that hold cells together (mushiness). Steaming vegetables tends to create more acid conditions, contributing to the sense that steamed vegetables maintain texture better than boiled. A curiosity is that the cook can confer firmness on some kinds of vegetables through low-temperature pre- cooking, which alters and sets pectins without dissolving components.
These concerns get us right to the core of American comfort food. Cooking potatoes for mashing is tied to the chemistry of water temperature, cell breakdown, and starch gelatinization. One achieves the most spectacular mashed potatoes when the potatoes cook evenly through, without overcooking outer layers. Overcooked means the cells completely break down and break apart, allowing internal starch granules to burst and dissolve. With extreme undercooking, you get a grainy texture that even ricing cannot eliminate. At the other extreme, when the potato is overcooked, starch whips into a quite proper glue. What you want is for the starch to cook (potato starch gelatinizes by 65 ºC, i.e. 150 ºF) without dissolving into the liquid to generate glue. This suggests the best potatoes for mashing will have been cooked at a low temperature until completely and evenly tender – the water may not ever come to a boil.
Boiling point is a break point in cooking. Without a pressure cooker, 212 ºF (i.e. 100 ºC) is as hot as you can cook food in water. At boiling point, what will have happened? Cells are disrupted and detached from one another. Starches have gelatinized and proteins are denatured. This is the reason a cake or a custard is completely cooked by 88 ºC (190 ºF). When cooled, the bread crumb will firm and gels will set.
Above that temperature sugars begin to change chemically, to the point we call “hard crack” (150 ºC / 300 ºF) at which they can cool to a glass or a crystal. This is lollipop and peanut brittle territory.
Until the solution temperature rises above hard crack, the only color affected will be natural pigments – either breaking down or changing due to new pH. In breads, around 280 ºF (140 ºC) you begin to see protein browning (the Maillard reaction, which involves amino acids and sugars), but there will have been no caramelized browning or candying, because concentration of sugars requires higher temperatures, and caramelization (the browning that occurs with sugar breakdown) is something that just begins around 150 ºC (300 ºF) for glucose – even higher for sucrose (you will first see this along the edges, where the container is hotter).
Candying has great value. When water is driven off, to the sugaring point, the product (a preserve, or candy) will be so concentrated that organisms we know can spoil food, or make it dangerous, are not able to survive. The solution is too concentrated – too osmotically challenging for most living cells to survive.
Going a few degrees higher, arriving at caramelization, is a different and most useful process. Flavor and color changes caused by caramelizing sugars give us brittles and toffees. And that browning reminds us of the reason frying and baking temperatures range from 175 ºC (350 ºF) and higher.
Browning (breads, french fries, tempura) requires those higher temperatures, because much of browning comes from the caramelization of sugars. (Note to self: ‘browning’ due to caramelization is not the same as the undesirable ‘browning’ in fresh-cut potatoes and apples that are exposed to the atmosphere)
Fermenting, Brining, and Pickling: There are times we actually want microbes to flourish in our foods, which is my segue to the many methods people have devised to alter and preserve food products employing microbes and chemicals. With plants, this often involves using microbes to break down sugars and starches into gases, acids, and alcohols, and in some cases to alter proteins (such as with fermented tofu.) Principal uses include production of breads, alcoholic beverages, soy-based products (often in brine), sauerkrauts & kimchi, and cacao seed for roasting. And remember, fermentation does not play a significant role in tea production, even though vendors will use the term.
All of these are fascinating processes relating predominantly to plants and plant products, because plant sugars and starches yield to agreeable forms during fungal and bacterial breakdown, while most animal products (save milk) come closer to rotting to a putrid mass rather than developing into a desirable, even celebrated food.
Hands-On: Breadmaking is a great opportunity to explore plants, chemistry, and food. I will lay this out for you as though a small group might go through it together. Let’s start with the simplest recipe and process, the same single-loaf process I use in teaching students.
For a class, I provide:
a work surface (we use extra large cafeteria trays, called market trays)
a simple measuring cup andspoons a small loafpan
an oven (hot pads,etc.)
wooden paddles, such as you’d use forpopsicles
a cloth (I like the the ones called “flour sack towels” available from many supplyhouses
a dough scraper (plastic ormetal)
whole grains of wheat (wheatberries)
wheat sprouts (purchased, or germinated on a moist paper towel)
gluten(powdered)
a bottle of wheat germ (stillsealed)
small paper bags for taking bread home
ingredients for breadmaking
bread flour (3-4 cups for eachparticipant
instant (rapid rise) yeast (1 Tablespoon per participant)
sugar (1 Tablespoonperparticipant) salt (1 teaspoon perparticipant)
hot water (1.25 cupseach)
olive oil (1 Tablespoon for the recipe, and additional for coating the tray andhands)
a can of spray oil with flour (baker’s releasespray)
Make Bread: It is useful to jump right into the process of making bread, in that you can consider other lessons while the bread rises After a communal washing of hands, I askeach
person to pour a bit of olive oil in his/her palm, and use that to coat both hands and work surface. Then, we:
- Measure 3 cups bread flour onto the worksurface.
- Combine that with 1 T instant yeast, 1 T sugar, and 1 t table salt.
- Shape the flour mixture to make an atoll – a donut-shaped mound – the center of which will be filled gently with the hot water.
- Bit by bit, use your fingers (sort of limply hanging into the water) to dredge in the flour, so as to make a slurry – attempting to keep the water from escaping the flour dam that was the atoll….
- Once there is no free water, pour 1 T of olive oil over the mixture, and proceed to create a dough that includes all of the flour andwater.
- Take a second to consider the dough. If it is stiff like modeling clay, you will need to incorporate more water. If it flows of its own accord, you need more flour. The dough should be soft but cling together as a mass. As you work the dough, add flour only if it remains wet and tacky – do not follow the temptation to add so much flour as to make it stiff. A soft dough is preferable to a stiff one.
- For the beginner, I teach kneading by the roll method. Gather the dough into a long, fat rod-shape, turn it so the rod runs straight away from you. Lightly (a dusting) flour your hands and the work surface, then tightly roll up the rod, like you are rolling up aribbon.
- Now, using your palms, roll the the ball back and forth until you once again have a rod several incheslong.
- Repeat the rod and roll procedure to make a tight ball into a rod, and so on – until your dough ball has some elasticity.. At this point, you can stretch the dough and it will maintain its surface, showing small blister-like inconsistencies in the surface. Moreover, your hands should be clean. If the moisture is right, your dough does not cling in patches to the work surface, and does not stick to yourhands.
- Time to let it rise. I ask students to pour a dabble of olive oil in their palms and use that to coat the dough ball. Set it on the work surface and cover with thecloth.
Forget the dough for a while. Let’s consider wheat, flour, and the botanical nature of what we are doing. Inspect a wheat kernel (“berry”). It is slightly cleft, not as smooth as a grain of rice, but very similar. Wheat (like rice, barley, oats, rye, and corn) is the fruit of a grass. These are grains, and they power our world.
I said fruit, and that’s precisely what I meant. A grain (kernel) is a single-seeded fruit – each was the pistil of a flower, which was one of several on a culm. [see Chapter 5, In Botanical Terms; Section 5 Nutrition, Sufferin’ Succotash] The grains differ from most other seed by investing starch storage in a curious tissue called endosperm. The endosperm was formed at the same time the egg was fertilized, and it grew courtesy of nourishment from the parent plant.
At the same time endosperm was bulking up, the embryo developed. So inside the grain there is an embryo (which we call the “germ”) that is dwarfed by a separate, starchy endosperm component. You will not be able to see this in the wheat kernel, because both the endosperm and germ are hidden inside the tan fruit wall, which botanists call a pericarp and most other people call “bran.”
If you grind (mill) a bunch of these wheat berries (raw), you’ll have whole wheat flour. If that were accomplished using an old-fashioned grindstone, you’d have “stone ground whole wheat flour.” But in today’s high efficiency flour mills, the tens of thousands of trillions of wheat kernels made into flour each year are broken and separated into individual components – bran, germ, outer endosperm, finer internal endosperm – and then recombined to produce typical packaged whole wheat flours. I hate to destroy the romance of whole wheat, stone ground flour, but it’s really just as well. People who lived on diets heavy in stone ground flours also ate so much stone dust as to grind their own teeth down to the quick. So much for romance.
Having broken the grain into components (called “streams” in the mill), let’s think about them. It would help to examine a drawing of the anatomy of a wheat kernel, which can be quickly discovered on-line (just search “wheat kernel”). From my perspective, the kernel includes four basic components (which boil down to three).
Bran. This is the brown or tan outer coating of a grain. When removed, two distinct tissues are included:
a. Pericarp. This is hard, tan, dry fruit wall. It is not rich in starches, but good as ruffage. Bran is coarse, and gets in the way of delicate textures. So it is not a favored ingredient when the objective is to make a beautiful loaf.
b. Aleurone Layers. The outer endosperm layers (just beneath the bran) make the most nutritious flour for humans diets, because they are richer in proteins and oils than the starchy inner endosperm. Aleurone cells are active in producing enzymes necessary to mobilize endosperm starch duringgermination.
Germ. In removing bran, the germ is also knocked apart from the endosperm. This is the embryo, consisting of primordial shoot and root tissue. The germ is rich in oils, and when exposed to oxygen it spoilsquickly.
Starchy Endosperm. The interior endosperm mills into the whitest flour, because it is incredibly starch-rich. But endosperm also has yellow carotenoids, which lend a creamy yellow color to fresh flour. Historically, cooks and clients
have considered that color undesirable, so many white flours are bleached (using any of several chemical and temperature treatments) to eliminate the color. Alternatively, aged flour (properly stored away from bugs) whitens over time as the carotenoids break down.
White flour is made from the starchy endosperm, and is therefore not as nutritious as whole wheat flours. To restore nutritional value, white flours are enriched with niacin, iron, thiamin, riboflavin, and folic acid. [From Wikipedia: “According to the FDA, a pound of enriched flour must have the following quantities of nutrients to qualify: 2.9 milligrams of thiamin, 1.8 milligrams of riboflavin, 24 milligrams of niacin, 0.7 milligrams of folic acid, and 20 milligrams of iron.”]
For our recipe, I specified “bread flour” – which reminds us that all of the proteins in flour are not in the aleurone layer. There are truly important proteins in the starchy endosperm, and they vary in concentration based on the kind of wheat being grown. Soft wheats, which yield flours used for “tender” breads, like cakes, have low protein content (about 8-10%). Hard wheats, which yield flours used for chewy breads and pastas, have 10-14% protein content.
That protein is the notorious “gluten”. Crucial to making beautiful yeast-risen breads, gluten creates the elastic infrastructure that sets to create structure when the bread is baked. The starches that make up most of the endosperm gelatinize to create the bulk and softness that surrounds the protein infrastructure. The gluten protein is not as water soluble as starches and sugars in flour, so manufacturers are able to wet and knead flour, then wash out starches and isolate pure gluten – which you can purchase. Almost any store with a strong offering of health foods will sell gluten, in bulk or in boxes.
Pour some gluten in a bowl and mix it with water. You quickly have a snotty and sticky mess. Students are astonished at this. A mass of wet gluten bounces like a superball. And it gets everywhere. It is worth the mess. Handling gluten is an important part of the story. In reality, gluten is not a single protein., rather a mix in which the specific proteins glutenin and gliadin predominate. They may be present in other grains, but only in wheat are these proteins both present and balanced to give dough the right consistency for the “well risen loaf.”
Finally, check out the germ. Open the bottle and give it a taste. This stuff is delicious, buttery and rich. No wonder it goes rancid so quickly. Once opened, the germ will spoil soon, even under refrigeration – so use it up. It’s a great embellishment on top of a bowl of cream of wheat.
When you eat germ, you are eating the embryo. If you have wheat grass (through germinating your own wheat kernels, or having purchased a square of wheat grass that is sold for juicing), take a few moments to compare the kernel to the seedling. Note the shell of the grain is probably still attached to the seedling, but it is soft and hollow. The entire endosperm has been spent, or rather mobilized and utilized. It was the energy in the endosperm starches that nourished the emerging wheat seedling.
So how did a rock hard grain become this soft green plant in just a few days? It takes 1-2 weeks to grow wheat grass, and people often start wheat grass by soaking the grains. As the grain takes in water, the germ generates hormones that stimulate cells in the aleurone layer to produce enzymes needed to break starches into sugars. Those newly available sugars provide the energy and building blocks required for growth.
People take advantage of this stage in germination in order to create malt, which is rich in those useful enzymes – something that can used break down starch for many purposes. We call this malt-generating process “malting”. That means people soak cereals (often barley) and keep them moist until germination starts. The germinating kernels are gently heat dried (not cooked), and ground, then used as an additive that promotes starch breakdown for many processes, most particularly in the manufacturing of beer.
As you can see, there is a lot to talk about here, and there is every chance you may have already given thirty minutes to these deliberations. Just in case, check your rising dough. I like to keep students absorbed in thinking about grains, talking about flours, inspecting wheat grass, and making a mess with gluten, so they completely forget the dough is busy. But if 30-40 minutes have passed, it is time to check.When we take that break and lift the towel, there is an audible gasp. With the instant yeast, this short time is usually sufficient for a doubling in size – which means it is time to deflate the dough.
I did not say punch down, because I encourage students to deflate the dough gently, using a modest kneading action. Then we let it relax for just a few minutes while preparing the loaf pans. That is pretty straightforward – just a coating of baker’s spray is sufficient. And don’t forget to turn on the oven (180 ºC or about 350 ºF)
We then shape the loaves in a very simple way. Flatten the dough to a rectangle (at least 6 by 8 inches). Then beginning at the edge nearest you, and using your palms and fingertips, begin rolling the dough very tightly. It will make a tense cylinder that gains length as you roll. Once rolled up, tuck the two ends into the loaf, and set it in the pan with the final seam on the bottom. If there are several people in the group (we have pans and oven capacity for 30 loaves), I ask students to write their names on the popsicle sticks and slide them upright in the pan alongside the loaf – so each person can reclaim his or her own loaf from the oven. You can elect to oil the top or not. Sometimes I will lightly spray the top crust with clean water, but that is unnecessary also. Cover with the cloth and set aside.
While the loaf is rising, make certain the oven is turned on and take a few minutes to talk about yeast and sugar.
Remember yeast is alive. The powdered form has been protected from heat and desiccation, so once it is moistened and given a bit of food (in the form of sugar), yeast springs to life, reproducing vegetatively – and actively. Even when oxygen is available, if sugars are plentiful yeast prefers to break them down through fermentation (We normally think of fermentation as anaerobic, a breakdown process that only occurs in the absence of oxygen. But yeast is different. For a more technical discussion of this, look up the Crabtree Effect. https://en.wikipedia.org/wiki/Crabtree_effect)
The products of yeast fermentation are carbon dioxide and alcohol. I will usually take a moment earlier in the session to dissolve a bit of sugar and yeast in a bowl of water, which by the time we get to this discussion has become a frothy, somewhat tasty concoction. Participants are amused at the foaminess, and most find the taste rich, reminiscent of the smell of rising bread and the flavor of some beers. That reaction is not universal – some people find the taste unpleasant.
This is the time to consider the rising process. Yeast, living off the tablespoon of sugar we incorporated in the recipe, has generated carbon dioxide that inflated the loaf – filling and stretching bubbles made possible by the gluten we moistened and aligned through kneading (you don’t really have to knead bread if it is fairly wet and left to its own devices for a while).
If this were sourdough, and we had used a starter, the work would not have been by yeast alone. There is an entire community of yeasts and bacteria that will do this job for you, and they will generate additional flavor compounds along the way.
Sugar has its own stories, as there are few plant products that have impacted human health and happiness so profoundly. Core to human genetic makeup is a predilection for sweetness in foods. We are told there are only four or five tastes that function apart from smell, and sweetness is one. At one time, we all learned that sweetness is detected by the tip of the tongue, but the concept of the “tongue map” is now regarded as a myth. What we perceive is a chemical property of many related compounds – most of which would be classified as sugars. In table sugar, sucrose, sweetness comes from the two sugar components (glucose and fructose), with fructose being perceived as the sweeter of the two. (The word fructose relates the common term “fruit sugar” – because fructose is the typical sweet agent in ripefruit.)
Regardless, sweetness is nearly universally pleasurable. The granular sugar we added to the dough may have come from sugarcane, which is a tropical grass, native to the Indian subcontinent. Before trade, imperialism, and globalism altered availability, most societies had paltry access to such processed and concentrated sweeteners, and relied on plant fruit and syrups. Native Americans had discovered the sap of Sugar Maple. Europeans doted on honey, and dried grapes to make sweet raisins. Dates were a staple in NorthAfrica.
Asian cultures domesticated peaches and apricots, persimmons, and sweet oranges, which formed the basis of their desserts and liquors.
These are all sources of fructose and glucose, and you can make bread using any source, whether sucrose (each molecule of which is one glucose attached to one fructose) or fructose or glucose – the energy does not have to come from processed white sugar. But some kind of sugar has to be included to power this living reaction. And added sugar may be needed to support a second (or in the case with some breads, even a third) rise. That additional sugar can come from the flour itself – recalling that slow breakdown of starches in the flour yields sucrose. If all of the alchemy works, the loaf we have formed will double – in about 30 minutes. Then it is time to put the loaf in the oven.
If time permits, it is useful to talk with the group about cane sugar. Because we live in a warm-temperate climate, we can cultivate sugarcane. I like to bring one culm (a stem, a cane) to the discussion, just in case participants have never seen this plant.
This plant is curiously unknown, though sugar and sugarcane have been major issues in world politics for centuries. Because our climate at The Huntington is warm temperate, we always have a few clumps of Sugarcane for interpretation, so I am able to harvest a stem (a culm) to show to classes. It is sobering to recount the story of sugar, its wonderful but often tragic consequences.
This grass, native to New Guinea, became one of the world’s most precious and desired commodities. We know the ditty that reminds us Columbus sailed the ocean blue in 1492, but he made that voyage again and again – four times. By his second voyage, Columbus had established plantings of Sugarcane in the Caribbean, plantings that yielded their first commercial crop in 1505. [search the Reader TimeLine for sugar] This was significant – Europe was determined to have access to sugar.
But the growing of cane and production of crystalline sugar is work-intensive. Labor was required, and native peoples of the Columbus’s “new world” would come to suffer their own tragedies due to disease and exploitation. Fate would not turn the native populations to wholesale sugar production. That would fall to another, old world land – Africa. Within a couple of centuries, millions of slaves were taken from their homes in Africa to this Newe Founde World to support the always- failing business of sugar production. The entire slave triangle that enriched New England was founded on sugar plantations in tropical America.
Examining the stem of Sugarcane, students begin to appreciate the backbreaking labor and complexities that needed resolution for sugar production. Juice had to be squeezed from the cane, collected, then boiled down to molasses that precipitates brown crystals. All of this required equipment, fuel to fire kettles, beasts of burden for hauling and milling, and human labor in the form of slaves.
Regardless how meager the provision, workers required both housing and food. Managing those complexities and exploiting those resources underwrote great swaths of world history for over four centuries. Sugar tells other stories also, giving us the ultimate food for thought. Like cotton, we are tempted to blame sugar for many of humanities ills, but paraphrasing support for the second amendment – sugar doesn’t harm society, people do……
Unfortunately, there is too little time in the course of events to investigate that topic satisfactorily. Bread bakes in 25-30 minutes. Students reach some threshold when two hours have passed and the aroma of fresh bread wafts from the oven. We clean up and fail to resist the temptation to sample one or more loaves.
I must end the discourse on breadmaking by reminding you that cutting into a loaf of bread, fresh and hot from the oven, is both delightful and sacrificial. Though cooked, the internal structure does not set until bread cools a bit. If you do cut into a loaf right from the oven, use a good bread knife and take care. By the time the internal temperature hit 90 ºC (about 195 ºF), the proteins were cooked and the starch gelatinized, but both remain soft. Externally, the loaf is closer to oven temperature; the crust is brown and resilient to a knife. This makes circumstances even touchier because it takes a serious stroke of carving to cut through the crust, while the interior is more like a soufflé. It is, therefore, easy to collapse the structure of the entire loaf. Minimally, you will discover this when spreading butter on a hot slice – the crumb sinks to a gooey wad.
I’ve worked through breadmaking with many groups, of every age, with two goals. Of course I want people to appreciate how the nature of plants impacts our lives in such fundamental ways as giving us our daily bread. But a second goal relates to personal competence and confidence. It is important to me that participants personally make and bake their bread. It is such a simple yet profoundly satisfying and useful skill, something you only need to conquer once.
Knowing that you can make your own bread means you never have to say you’re sorry.
Breadmaking is just one of several complex inventions that showcases relationships between science, art, culture, and history . Today, with the expanded access to information through the internet, you can explore similar relationships with many related processes. If this is of interest, check out some of the following:
Making of Sauerkraut and Kimchi
Manufacture of Soy sauces, Tofu, and many complex soybean-based products
Manufacture of Worcestershire sauces
Spirits – the making of beer, wine, and hard alcohols