How Can We Recycle the World’s Food Supply? It Might Involve Leftovers.

Bryan Quoc Le
Jan 9 · 13 min read
Photo: Maria Teneva/Unsplash

The environmental impact of food waste is staggering.

1.4 billion hectares of land, or 34% of the world’s total agricultural land, is used to grow food that’ll eventually end up in a landfill. Most of the food waste disposed in a landfill decomposes anaerobically and generates the powerful greenhouse gas methane, increasing our carbon footprint. Agriculture accounts for 69% of the world’s water usage, and yet one third of that water is wasted as uneaten food.

Unfortunately, the United States is the largest producer of food waste, with food waste as the leading occupant in American landfills.

In 2017, a study was conducted by the Natural Resources Defense Council (NRDC) to evaluate the amounts and types of food waste produced by consumers in the United States. Researchers collected food waste from Nashville, Denver, and New York City and categorized the waste across several categories. According to the study, 23% of consumer-level food waste in the United States comes from leftovers and makes up the highest fraction of edible food waste.

Using the 2010 food waste data provided by the USDA as a conservative estimate, that leads to a whopping 30.6 billion pounds and $37 billion worth of edible food.

That’s a lot of economic value going down the drain.

While composting or re-purposing edible food for animals can take food out of the landfill system, most of the capital, energy, and resources spent growing, harvesting, fertilizing, storing, and transporting food is still lost.

The highest possible net energy return and lowest environmental impact is to reuse human food for human consumption.

“1.4 billion hectares of land, or 34% of the world’s total agricultural land, is used to grow food that’ll eventually end up in a landfill.”

Many environmentally conscious startup companies are working to curb food waste by upcycling edible waste products into new food. ReGrained rescues the leftover grains of brewing beer and produces a high-nutrient flour for making energy bars. Toast Ale brews a pale ale using surplus bread as a source of fermentable carbohydrates. Treasure8 is a food technology company dehydrates excess fruits and vegetables to make snacks. These are just a few examples of a larger ecosystem of food recycling companies.

However, food waste in the kitchen and restaurant remains a large fraction of food waste that is difficult to capture at scale.

There could be another strategy to reduce food waste at the consumer level.

And the answer might lie in a mold.

Aspergillus oryzae, also known colloquially as koji in Japanese and qu in Chinese, is an edible mold that’s been used for thousands of years to prepare fermented soybeans, miso, soy sauce, sweet drinks, desserts, and rice wine. The term koji has been adopted by most Western chefs and cooks, and so I’ll continue to use koji to refer to this species of mold. Koji molds are grown on a solid nutrient source like steamed rice, wheat, or soybeans. In contrast, most food-based fermentations require the microorganisms to be submerged in a liquid, like how yeast brew beer or bacteria ferment milk into yogurt.

These microorganisms are distinct in that they secrete enzymes into their surrounding environment that break down and digest complex food molecules into simpler molecules that they can absorb. The power of koji fermentation truly lies in their enzymes, which humans have exploited to transform bland food ingredients into remarkably tasty foods for generations.

Photo: Jinwoo Lee/Pixabay

Koji molds contain the genetics and biochemical machinery to produce hundreds of different enzymes, but the most important ones for food are their proteases and amylases. Proteases digest proteins into amino acids while amylases digest starches into sugars, both of which impart flavor and taste and become the precursors to even more complex flavor formed from secondary fermentation by other microorganisms.

Any food rich in starch and protein that touches these enzymes slowly decays into a rich soup of these two basic building blocks of flavor. Koji enzymes are quite powerful and continue to be useful for many industrial processes involved in the food and chemical industries. In their purified form, these enzymes are used to produce sugar syrups, cheese powders, bread doughs, clarified fruit juices, alcoholic beverages, seasonings, and sauces.

Photo: Renato Canepa/Pixabay

In more recent times, koji has experienced a revival in the home and restaurant kitchen. Noma, the Michelin-starred Scandinavian restaurant led by chef René Redzepi, uses koji to ferment many of the ingredients they use in their dishes. Several of their experiments have been conducted atthe Nordic Food Lab in partnership with the Department of Food Science at the University of Copenhagen and documented on their website. Noma recently released a New York Times best-selling manual, the Noma Guide to Fermentation, that describes how to grow and use koji to craft delicious dishes.

Other high-profile chefs and experimental cooks are exploring the culinary world of koji. Chef David Chang of Momofuku fame has used koji to produce alternative misos and soy sauces using non-soy legumes, grains, and nut butters through the Momofuku Culinary Lab. Chef Jeremy Umansky of Larder, a delicatessen in Columbus, Ohio, and leading koji explorer Rich Shih of OurCookQuest have teamed up to write the upcoming cookbook titled Koji Alchemy, which details many of their koji recipes and experiments.

What’s so special about koji when it comes to kitchen cooking?

Like I mentioned before, the proteases released by koji mold break down proteins to form peptides (or protein fragments) and amino acids. One of the key elements to flavor comes down to the presence of the amino acid glutamic acid, or glutamates, which is responsible for the rich and hearty umami flavors in savory foods. Monosodium glutamate, or MSG, is a form of glutamate that used industrially to impart umami while koji can do it naturally. Ribonucleases are another group of koji enzymes present in lower concentrations that break down nucleic acids (like DNA and RNA) into nucleoside phosphates. Two nucleoside phosphates, inosinic acid and guanylic acid, are intense umami activators and work in synergy with glutamic acid to exponentially heighten umami flavor. The amylases released by koji mold also add sweetness by transforming bland starches into glucose and other simple sugars.

Photo: congerdesign/Pixabay

All these compounds alone can add enhanced taste to a food, but when a food containing these compounds is cooked at temperatures above 140 degrees Celsius, they undergo the Maillard reaction to form hundreds of flavor compounds. In particular, the combination of glutamic acid and glucose form strong meaty and umami-inducing flavors under Maillard conditions. Chefs, amateur cooks, food scientists, and gastronomic experimenters have exploited koji fermentation and koji enzymes to express very intense, deep flavors in foods and have applied it to ancient grains, pickles, fermented drinks, root vegetables, coffee beans, cheeses, meats, and even insects.

The process of growing koji is relatively straightforward but requires time, patience, and a high attention to detail. Koji begins with spores called koji-kin, which serve as the seeds that germinate into koji mold. Koji-kin is usually purchased directly from a Japanese koji-kin manufacturer (there are only six left in Japan) or a third-party dealer that sells their prepackaged koji-kin. Koji-kin can also be generated from matured koji mold. Koji-kin is first mixed by hand with freshly steamed grains or beans and spread thinly in a shallow pan or wooden tray to be cooled to about 35 degrees Celsius. The inoculated material is placed in an incubator set to 30 degrees Celsius with a source of water to generate high humidity. At several time points, the growing material is mixed by hand to make sure the koji is maintained at the proper temperature and oxygen levels because koji mold produces heat and consumes oxygen as it ferments.

Photo: Jing/Pixabay

Temperature and humidity are key parameters to keep an eye on. Too high of a temperature and the koji dies. Too low of a temperature and the koji stops growing. Too dry or too little oxygen and the koji becomes dormant.

A small patchwork of amateur cooks has designed do-it-yourself instructions to grow koji in the home kitchen. The current iteration through which many have found success is to take a cooler and elevate a shallow metal pan containing the inoculated material in it. Water is filled below the pan to serve as a water bath. An aquarium heater is placed in the water to regulate the temperature to 30 to 35 degrees Celsius. The cooler is then closed to allow the fermentation to progress in a moist, warm environment for 30 to 40 hours to give white-yellow, fragrant rice mold. The koji rice is then combined with a protein or starch-rich food material to provide a substrate for the koji enzymes to act on and form sugars and amino acids. This is the basis for most koji fermentations.

“Chefs, amateur cooks, food scientists, and gastronomic experimenters have exploited koji fermentation and koji enzymes to express very intense, deep flavors in foods and have applied it to ancient grains, pickles, fermented drinks, root vegetables, coffee beans, cheeses, meats, and even insects.”

I’ve personally attempted to grow koji on rice using a minimalist approach that involved our apartment oven with the pilot light on as a source of heat, lovingly spraying the fermenting steamed rice with water every few hours, taking the temperature with a digital thermometer, and watching the mold spread across the grains of rice. But due to a combination of irregular heating and poor moisture control, the koji quickly blossomed into a yellow-green fuzz after a day and a half, which is usually a sign that the mold matured and formed spores.

I removed the koji rice to cool, dried it in the open, and tried one of the rice kernels, which tasted a little bit like dirt. Unfortunately, I learned that koji mold becomes earthy and bitter in flavor during the sporulation phase of its life, so there’s a narrow window between when koji is still white, fragrant, and delicious, and when koji starts to mature into something less than edible. I’ve since resigned myself to experiment with koji fermentation using commercially prepared koji rice to ensure that I don’t have to go through that again.

Growing koji is not for the faint of heart.

Another challenge with fermenting foods using koji is that the foods need to be fermented at room or warm temperatures in the presence of some microbial hurdle to ensure the foods are safe from pathogenic and spoilage microorganisms. If the fermenting food were heated above the temperatures that microorganisms can survive, the heat would deactivate the koji enzymes and lead to little to no biochemical changes. In the case of miso, soy sauce, and fermented beans, high levels of salt or brines at 5 to 18% salinity are usually used to protect the fermenting food. As for rice wines, high levels of alcohol produced in secondary fermentation by yeasts is sufficient to keep the wines safe. Koji-infused foods can also be co-fermented by other microorganisms that produce protective acids, such as in the case of vinegar or lactic acid beverages.

Photo: Matthew Lakeland/Unsplash

But in each of these cases, the hurdles used to protect the foods from spoilage changes the environment in which the enzymes operate. pH, salinity, and alcohol concentration all reduce the stability and reaction rates of the koji enzymes, which increases the time it takes for full fermentation and break down to complete. This is reflected in the fact that it takes at least six months for high salt, protein-rich products like miso and soy sauce to ferment. Even when the fermenting product is heated to 60 degrees Celsius, the highest temperature that proteases can survive before they break down (amylases are more heat resistant), it can still take three to six weeks to fully degrade. Fermentations that rely on starch-rich products like rice wine take less time, about two weeks. However, that’s still quite a long time to wait.

Now, there is one koji strain that could make for an interesting substitute.

Aspergillus awamori (also known as Aspergillus luchensis) is a black form of edible koji used exclusively in Okinawa, Japan to produce awamori, a distilled hard liquor made from Thai long-grain rice. The black koji belongs to the same genus as normal koji and produces many of the same enzymes as the latter. However, black koji is distinct in that it also produces citric acid, which lowers the pH of its surroundings and protects fermenting substrates and mashes from infection by unwanted microorganisms. Its enzymes are resistant to acid and can still function optimally at pH 3 and below. These two features of black koji are what make it desirable for producing rice spirits in the high heat and humidity of the Okinawa islands, where fermenting rice is prone to spoilage.

They’re also the features that could make food waste transformation a practical reality.

Aspergillus awamori could be harnessed to quickly degrade leftovers into new ingredients in a microbially safe manner without relying on salt or alcohol. By combining food leftovers with A. awamori enzymes and a sprinkling of citric acid (enough to get below the microbial danger zone of pH 4.6) then heating the mixture at 50 degrees Celsius (right above the effective growth temperature of microbial pathogens like E. coli but still within the optimal temperature window for the protease enzyme to function) over a few days, what you would get is a nice mash of broken down nutrients from the leftovers — something like a warm soup of sugars, amino acids, peptides, and nucleic acids. After straining, you would have a clean broth rich in simple nutrients harvested from old leftovers that would have otherwise gone to waste.

Photo: Esmée Scholte/Free Images

The nice thing about using citric acid as the protecting acid is that it can be easily precipitated and removed at the end of the digestion by adding calcium carbonate (basically, Tums antacid), which reacts with citric acid to form an insoluble calcium citrate that can be filtered off. The result is that the mixture doesn’t end up sour at the end of the digestion.

Imagine a home appliance where you throw in last night’s leftovers, add a packet of enzyme powder, then set it and forget it. Something like a washing machine, except for food.

Every night, you keep adding your leftovers (half-eaten meat balls, pasta noodles, breakfast burritos, scrambled eggs, oatmeal, forgotten cheese, etc.), until at the end of the week, the appliance switches to pasteurize mode to deactivate any remaining enzymes.

At the end of the cycle, you just add in a second packet of calcium powder, then open a spigot to filter out the solids.

Out comes a rich, nutritious (and hopefully tasty) broth made from the most basic components of your entire week’s meals that you can drink on your way to work or use as a base for a soup.

Photo: congerdesign/Pixabay

The broth could be collected by a local processing facility that uses it as a resource to extract amino acids, sugars, and other nutrients for producing new foods and ingredients.

The broth could even be simply dumped down the drain, which would still have a smaller environmental impact than the same mass of solid food waste dumped into a landfill, taking up precious land and emitting methane gas.

(Hello IndieBio, do I have a startup idea for you…!)

The truth is that, at this point in time, there might be little economic reason to recycle your leftovers in the kitchen when so much food is already being produced around the world, especially in developed nations. But imagine a future when food is more expensive and nutrition is hard to come by due to increasing drought, pestilence, poor crop yield, or any number of climate-related impacts on food production.

A kitchen-top food recycler might just do the job.

“Imagine a home appliance where you throw in last night’s leftovers, add a packet of enzyme powder, then set it and forget it. Something like a washing machine, except for food.”

There are other human needs where a food-digesting appliance might find a market before maturing into a full-fledge machine designed to recycle food at the point of consumption. Patients who suffer from gastrointestinal injury or have recently completed specific surgeries are recommended to go on a clear liquid diet. The appliance could be used to produce customized, high-nutrient liquid broths that are suitable for such diets. The appliance could also be used for people who generally suffer from poor digestion and require their foods to be pre-digested.

Or the appliance could simply be used to produce very tasty, customized broths and stocks for the home cook or restaurant chef (a not-so-instant Instant Pot).

These are but a few potential ideas and certainly do not capture the whole range of technological possibilities that could help improve the world.

Photo: Dane Deaner/Unsplash

I pieced this essay together because I’ve been thinking about the applications of koji and koji enzymes for several years. A lot of these thoughts have been bouncing around my head as I’ve read more about the behavior and characteristics of koji molds on food, and I wanted to finally write all of this down.

I believe there’s amazing potential between these ancient molds and sustainable biotechnology. Koji enzymes are already used industrially for some of these purposes, like digesting cellulose to produce bioethanol, but I always wondered about applications at the consumer level that could help people like you and me curb food waste and help the environment directly from the kitchen.

I would love to chat more and share ideas with others interested in the crossover of food, technology, and sustainability topics.

Thanks for reading!

Bryan Quoc Le

Written by

Food scientist and writer capturing stories about food, nutrition, and biotechnology | bryanquocle@gmail.com | https://bryanquocle.journoportfolio.com/

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