S6C6: Agriculture & Food

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a) Harvesting biological processes

I will try to keep my promise made in the previous chapter that things were not going to be very technical for Part B of this sixth and last series, yet this doesn’t mean we will not dip our toes into chemistry from time to time. And in fact, we need to do this straight away to understand the nature and purpose of agriculture.

Its nature is to offload the biochemical burden of making food or other useful macromolecules and then harvest those for our benefit. When I say offload, I am not implying a purely exploitative behaviour, when it comes to food this is the way the food chain works and the very concept of food and nutrients absorption were tackled in S2 Section 2.a. Simpler organisms get nutrients from the soil or the sea, tap an energy source like sunlight to perhaps manufacture new cells and carry out other biochemical processes such as reproduction, whether sexual or asexual, and then these organisms get ingested by others who metabolize their macromolecules to grow their own body, and so on until the apex predators of each food chain, who tend to be omnivorous or carnivorous – these are technical terms and the former refers to the consumption of both animal and plant molecules whereas the latter will only ingest, or nearly exclusively, animal tissues and mostly comprises animals though there are also some carnivorous plants.

Our ancestors may have been hunters and gatherers, but along the way we systematized the growing of crops, the raising and killing of animals, be they aquatic or land based (livestock), and the management of forests for their wood. This leads us to the purpose of agriculture, which is the improvement of productivity, reliability and safety in the supply of food and other useful organic products. We will come back to the productivity aspect in the next section.

There is a wide variety of crops and the use of these plants is not solely as food products; some of them like cotton will be used for their fibre and other biomass types can be processed into fuels. One crop may even be sought after for more than one role, for instance rapeseed can be grown for its oil and also be used to produce biodiesel. Crops extracts nutrients from the soil, we saw this in the case of plants in S2 Section 2.f, and the photosynthesis process “uses energy from sunlight to fuel the metabolism of plants and converts carbon dioxide into carbohydrates such as starches and cellulose, releasing oxygen as by-product” – this is quoting from S1 Section 7.f.

Almost a third of primary crops, the name for unprocessed crops, whether it is by volume and value, is represented by cereals with the big three consisting of wheat, rice and maize. Then comes sugar crops headed by sugar cane, and then the trio of fruits, vegetables and oils, be they edible or used for cooking.

The growing of livestock traditionally involved grazing and animals living off the land but this is no longer always the case and they are often wholly or partially fed in warehouse-like environments in order to accelerate their production of tissue (meat), milk or eggs. Overall, consuming meat turns out to be a very inefficient process as opposed to consuming plants because it layers in an additional metabolic process plus homeostasis for the already existing tissues to remain alive, which is energy intensive.

Aquaculture is to fishing what animal husbandry is to hunting. It is not limited to fish but covers all types of sea and freshwater food, including molluscs and algae. Very often, like in animal husbandry, there are enclosures involved. Interestingly, the cultivation of kelp and seaweed removes carbon dioxide from the atmosphere and therefore benefits from some political support, unlike the slash and burn method of clearing soil for planting crops such as palm oil.

b) Productivity and resistance in agriculture

The reason we became sedentary and created new tools over time is because it made sense from a survival standpoint. Food to feed ourselves but also to barter or sell for a certain amount of money so that other products could be bought. In terms of methodology, this led to increasing specialization and technologically the result was a quest for better equipment and species with improved characteristics. In this chapter, I will not dwell on the mechanization aspect and only state that it served to replace human labour – this may have displaced a vast number of jobs but one needs to bear in mind a lot of these were backbreaking, monotonous and resulted in higher production cost and therefore increased prices at the customer end.

When it comes to crops with better characteristics, historically this was achieved by crossing species and breeding the best individuals to have more offspring. However, nowadays, thanks to DNA recombination and molecular cloning, it is possible to alter the genetic material of plants and artificially create new phenotypic traits such as flavour, colour, size and the absence of seeds. I include a link to the Wikipedia entry for molecular cloning at the end of this chapter if you wish to read more on this topic.

More broadly, and before genetically modified organisms (GMO) were a thing, there was a surge of crop yields driven by a confluence of processes and products sometimes swept under the catchy name of Green Revolution although it happened at different times and in a variety of manners across the world over many decades. Controlled irrigation was part of the equation, alongside the breeding and use of high-yield varieties and the application of chemical fertilizers and pesticides.

Fertilizers are no more than the topping up of the main macronutrients required for plant growth: nitrogen, potassium and phosphorus. Overexploited soils tend to lose nutrients concentration and the high-yielding species also tend to require more nutrients for their comparatively accelerated growth. This has led to an increasing reliance on fertilizers and the pollution of aquifers.

Pesticides are there to try and eliminate pest as far as possible – and pest is not an intrinsic property, it is a name we humans affix to organisms that we deem inconvenient. Pests can refer to insects, fungi, bacteria or even some plants we would then call weeds. The issue with pesticides is that they can be toxic for other animals, including humans.

Furthermore, many types of chemical products can be sprayed on primary crops after harvest so they keep their fresh appearance during the transport and distribution stages. For example, maleic hydrazide is an herbicide and sprout inhibitor so it can be used to induce dormancy during transport and ethylene can be sprayed to force the ripening of fruits and vegetables. Ever wondered why some of the imported fruits you buy in hypermarkets look lush one day, overripe two days later and good for compote the third day?

And finally, the least contentious probably, is the use of temperature as a variable to slow down the metabolic process. The cooler the temperature, the slower chemical reactions take place, as if in slow motion. This is why the cold chain really does wonders and frozen food is antonymous to fresh food but doesn’t imply processing.

c) Vertical farming and cultured meat

Fertilizers, irrigation, pesticides, all of these could be described as controlling the farming conditions and, accordingly, the logical extension to this involves stepping up the regulation aspect to include key variables such as temperature, humidity and lighting. For temperature and humidity, the archetype of a controlled environment is the greenhouse. They may be somewhat more expensive to operate compared to a standard plot of land but they allow for farming throughout the year as well as in regions where some crops would not be viable because the climate is not propitious. This has the side benefit of saving on the cost, wastage and pollution associated with long transport legs. For lighting, grow lights can be used that replace or supplement sunlight and these can be focused on the most effective spectrum frequencies for the photosynthesis process of each species.

The logic is still not at its end and can be pushed further. The availability of arable land restricts the size of crops that can be farmed and only one crop can be farmed at a time. However, what if we can abstract the soil away from the surface of the Earth and create multiple horizontal layers? This is a reality called vertical farming and there is nothing inherently astonishing or suspicious about them, a good analogy would be the gradient separation of roads and train tracks, using the vertical dimension to increase the density of traffic (refer to S5 Section 1.c).

Going even further, why use soil as the medium from which to extract nutrients? The first alternative in soilless farming is called hydroponics and has the roots of plants dipping directly in aqueous solutions rich in nutrients and minerals. Perhaps counterintuitively, this reduces water usage to produce similar volumes of crops. Nevertheless, not every plant can withstand long periods of uninterrupted exposure of their roots in water and, for those, aeroponics provides a good alternative. This method uses the same type of solution as in hydroponics but it is being sprayed over the roots, like mist, at regular intervals and the content that is not being absorbed is collected and reused, thus forming a closed loop, though one that requires more external energy to operate. An additional advantage of aeroponics over hydroponics is the improved gas exchange at the root and stem level.

This type of soilless and controlled environment paradigm can be carried over to animals in what is called cultured meat. This should not be mistaken with plant-based meat which, as the name suggests, contains vegetables, many of them rich in proteins such as peas and soy (in the form of tempeh or tofu), and seeks to replicate the mouth-feel of meat. Cultured meat is not an alternative to meat, it is an alternative to raising and killing animals to grow and sell meat. Technically, the proposition is more challenging compared to the farming of crops, however elaborate the method might be, because it requires mastering the differentiation and growth of stem cells into muscle and possibly fat cells, depending on the desired outcome. Stem cells can replicate indefinitely and be turned into a variety of cells such as immune or nervous cells, not just muscle or fat. It is not even necessary to kill an animal to extract stem cells from it before they can be cultivated in a lab. The culture medium has all the nutrients and minerals required for the cells to divide and multiply the original number until they form muscle tissue, the meat the omnivores among us consume.

It sounds too good to be true, and it is because I have skipped an important step here. Meat appeals to our taste buds not merely because of the amino acids it contains but also because it has a certain texture and structure and these are variables that change depending on the type and quality of the meat. As a consequence, the growing and differentiating of stem cells needs to be engineered to partially replicate these aspects in a way that consumers will enjoy. The main technology at this time uses scaffolds in the form of extracellular matrices to direct the organization of the three-dimensional cellular organization but layering and more broadly 3D-bioprinting technologies have also had interesting results. I have included a link to the Wikipedia entry for extracellular matrix at the end of this chapter if you are interested in reading more.

Somewhat surprisingly, yet not completely unexpectedly, many people consider cultured meat a horrifying prospect. This clearly is a first-take, unreasoned reaction, the same way a proto-human may have been disgusted at the idea of eating cooked rather than raw meat. Indeed, one needs to be objective about the drawbacks of meat coming from livestock: it contains a lot of bacteria, there is a lot of wasted parts and it is fundamentally unethical – provided one subscribes to the idea of “you shall not kill” and the biological understanding that species are linked through an evolutionary continuum without any meaningful differentiating threshold other than the absence or presence of a nervous system conveying pain.

d) Food processing

Most primary crops are not consumed in their raw form and undergo one or several stages of processing. The objective of the first level of processing it to render the food edible, this can be the butchering of animals for their meat or the milling of cereal grains to produce flour. The second level, we can capture under the umbrella term of cooking, and we will look into this in the next section. In our modern societies, there is yet another level of processing where the food is supplemented with colourants, salt, sugar and other additives to ensure a longer shelf life, enhance its taste and look, and elicit some cravings in the consumers allowing the manufacturer to sell more products to them over time.

The best ways to increase shelf life are as follows:

Removing the parts that are more susceptible to oxidation or may contain bugs. This is why supermarkets sell white rice rather than the more nutritious less-processed brown rice.
Eliminate pathogens through pasteurization by exposing them to heat without altering the properties of the food. This is commonly used for liquids such as fruit juice and milk.
Packaging is essential in avoiding oxidation and exposure to pathogens present in the air and various surfaces the food may come in contact with. Vacuum packing will not only provide such isolation but it also prevents oxidation and the growth of fungi and bacteria.
As mentioned earlier, maintaining a cold chain will also ensure a slowdown of the biochemical reactions and reduce the risk of pathogens multiplying. It may also be necessary to retain the shape and texture of the food being transported or stored.
The freezing of food pretty much halts the growth of bacteria by turning liquid water into ice and this, coupled to low temperatures, slows the decomposition of organic matter. The pace at which the freezing occurs, and the temperature it is lowered to, also affects the texture of the food. Flash-freezing, which is the exposure to cryogenic temperatures, reduces the size of the ice crystals that are susceptible of damaging cell walls. I include a link to the relevant Wikipedia entry in the last section if you are curious about this process. Freeze drying is different and involves the dehydration of frozen food by lowering the pressure so that the ice is sublimated, transitioning from the solid phase to the gaseous one without transitioning by the liquid phase (refer to S1 Section 2.e titled “states of matter and phase transitions”).

There is a very good analogy that can be drawn between the electricity grid, the subject of Chapter 4, and the food industry. Agriculture is the equivalent of the power generation assets, the transmission lines would be the freighting aspect, by sea, land or air, and the distribution can be done under various formats, from the wholesalers and hypermarkets, down to the convenience stores. Moreover there are smaller decentralized producing assets such as people’s own gardens and the various voltage step up and down can be compared to the multiple levels of food processing.

e) Cooking

Technically, cooking refers to the use of heat to make the food safer to eat as well as more digestible and palatable. The palatable aspect is significant as it is an integral part of the tasting experience, as highlighted in S2 Section 2.e on the gustatory system.

One of the first techniques that may come to mind is boiling and in the context of cooking we are not interested in the phase transition but in the temperature of water, or whatever the working fluid is. Increasing the temperature allows for the transfer of heat by conduction to the food immersed in the liquid medium. Where the food is not immersed but placed above the boiling liquid, the technique becomes steaming and it is the vaporized water molecules that transfer heat to the food, keeping it moist in the process.

There are two variations of boiling that have much in common and both avoid direct contact of the food with the working fluid, which may result in its dilution or unwanted hydration. The first is bain-marie, which is effectively the use of a heated water bath as the source of heat for the food container. This method results in a diffuse heat being applied and can be used for slow cooking, without risking exposure to high temperature, or just to warm food up. The sous-vide technique is similar but there the food is sealed in a pouch and immersed in the water. This avoids mixing and dilution of the food and the cooking can happen for several hours at low temperature (think 55 to 70°C) thus preserving moisture in the food and preserving most of the original texture.

Moving away from liquid as a medium, grilling uses heat transfer by radiation through the air, though in the case of a pan or other surface most of the heat would be conveyed by conduction. The high temperatures involved will generally trigger a change in the texture of the food, especially on the outside surface which is more exposed. This can help seal the juices in, as in searing, or it can caramelize the sugars contained in the food. On the other hand, baking uses both conduction, at the point of contact, and convection through the air to cook the food. You may want to refer to S1 Section 9.d for an explanation of the differences between heat transfer by radiation, convection and conduction.

Whilst not falling under the remit of cooking in the technical term, I will also mention a few additional culinary methods:

Marination tends to have two objectives, being the addition of flavours and the tenderization of meat. This softening of the tissue is actually a breakdown triggered by the enzymatic content of the marination or its acidic nature and this allows for incremental moisture to be absorbed, making for a juicier end-product.
Pickling uses aqueous solutions that are salty and highly acidic such as vinegar in order to prevent enzymes from facilitating some chemical reactions and microorganisms from proliferating. This extends the shelf life of products and also imparts them with a different texture and a pungent taste, which can call for an acquired taste (refer to S2 Section 8.f for an explanation of the process behind acquired taste).
Curing is the addition of salt to food in order to draw moisture out through osmosis by creating a solute-rich environment. This reduces the growth potential for microorganisms and is thus an effective method of food preservation in a dry storage environment.
Seasoning is a catch-all term referring to the addition or enhancement of flavours by using herbs, salt and spices.

f) Trivia – Bread

It is difficult to overestimate the cultural importance of bread in most regions of the world, with the notable exception of Southeast Asia, North Asia and the Pacific where rice is the main cereal crop and is consumed as grains or noodles. Cereals are rich in carbohydrates and therefore deliver most of the energetic content in the diet of pre-modern societies. This explains why offering bread to a stranger is a sign of hospitality and why wasting it is frown upon.

The most popular cereal for making break is wheat, in part because its high gluten content imparts elasticity and an enjoyable spongy texture to the dough. A large variety of other wheat species can be used besides common wheat (also known as bread wheat), such as spelt, as well as other grains including maize, barley, rye and millet. Often, flours can be mixed.

The other key differentiating factors between various types of bread, and here I am sticking to the savoury variations, is the presence or not of leavening agents such as yeast. When present, the chemical reactions occurring during the baking process will release gases such as carbon dioxide which will create air pockets within the starch matrix. In their absence, the bread will not rise and this would be the case for most flat breads although a few of them are leavened. It should be noted that many flatbreads contain dairy ingredients such as milk or yoghurt.

Variety in shapes and grains, and variety in baking apparatuses, from the wood-fired pizza oven to the ceramic or clay used in tandoors to prepare flatbreads from South Asia all the way to North Africa by way of Central Asia and the Middle East.