What Would It Take to Feed the Entire Human Population with Nothing but Mycoprotein?

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GUEST AUTHOR: Tomas Linder, PhD | Associate professor | Department of Molecular Sciences | Swedish University of Agricultural Sciences | Tomas Linder on Facebook

Previously I wrote about why I believe cultured meat can never play more than a marginal role in global food security. At the end of that post, I included a quick comparison with mycoprotein––a meat imitation product made from the soil-living fungus Fusarium venenatum. I argued that because F. venenatum and other fungi can use simple growth substrates such as organic acids, which can be synthesized chemically from atmospheric CO2, this would make it possible to produce food without photosynthesis. That ability in combination with the relatively fast growth of F. venenatum led me to suggest that the mycoprotein production process would actually have the capacity to feed the entire human population.

Then I began thinking about just how feasible that idea would be. What if we had to feed the entire human population with nothing but mycoprotein? (Asteroid impact? Nuclear winter? Alien invasion?) I’m a sucker for thought experiments known as “Fermi problems”, named after the Italian physicist Enrico Fermi. The idea is not to arrive at an exact estimate but rather get a sense of scale, a ballpark figure. You start with simplified but more or less sensible assumptions and then see where the math takes you.

So here goes. Let’s assume that we need to feed the entire human population of the near future––say 10 billion people––with nothing but mycoprotein. Let’s also assume that mycoprotein will satisfy all nutritional requirements of the average individual––which seems highly unlikely but let’s go with it for now. According to the British National Health Service, an adult man requires 2 500 calories per day to maintain his current weight while an adult woman requires 2 000 calories per day. For the purpose of this thought experiment, we will assume that the entire future human population consists entirely of adults with a perfect 50-50 gender distribution, which translates to an average caloric requirement 2 250 calories per person per day.

Quorn Foods––the makers of mycoprotein products––report that the energy content of mycoprotein is 850 calories per kg. So in order to satisfy the daily caloric requirements of the average individual of the future, we would need:

2 250 calories per person per day/850 calories per kg = 2.6470… ≈ 2.6 kg per person per day

The Quorn factory in the north of England has been reported to produce 60 metric tons i.e. 60,000 kg of mycoprotein per day in their three bioreactors (pictured). This means that a factory of equal size and output would be able to feed:

60,000 kg per day/2.6 kg per person per day = 23,076.9230… ≈ 23,077 persons

So to feed the entire human population of the future, would require:

10,000,000,000/23 077 = 433,331.8888… ≈ 433,332 mycoprotein factories

At first glance, this number might seem large––just under half a million factories. But remember that we are talking about feeding 10 billion people with mycoprotein only. The problem is that 10 billion is just too big a number for us to grasp. So let’s chop it up into smaller bits. Instead, imagine that we have to feed the entire current population of the US (327 million people) with nothing but mycoprotein. We would need:

327,000,000/23,077 = 14,169.9527… ≈ 14,170 mycoprotein factories

This number feels more like it’s in the realm of the possible. For comparison, there are roughly 5,000 Walmart stores in the US right now. At the same time, the US has just over 2 million farms. So the idea of building 14,000-ish mycoprotein factories in the US seems fairly reasonable (even if the idea of all US citizens happily eating nothing but mycoprotein any time soon isn’t).

Let’s pick apart this oversimplified estimate a bit. The productivity value for the English mycoprotein factory as given above––60 metric tons per day––is based on feeding sugar to our F. venenatum. If we were to use sugar as a feedstock for fungal cultivation, we will obviously require agricultural land. In my previous post, I had pointed out that it’s also possible to grow fungi like F. venenatum on acetic acid as the only source of metabolic carbon. Acetic acid can be synthesized directly from atmospheric CO2 and would therefore not require any agricultural land. However, F. venenatum will grow slower on acetic acid, which will bring down the daily output by a factor of maybe two to four. This means that we would need two to four times as many factories to keep up with the daily caloric requirements of the US population. That would still seem like a reasonable number (30,000-60,000 factories) in a doomsday scenario where conventional food production in the US would collapse entirely for whatever reason.

Finally, let’s take a quick look at just how you go about making acetic acid (CH3COOH) from CO2. There are two main routes from CO2 to acetic acid–one involves chemical catalysis and the other biocatalysis. Methanol carbonylation is the most common way to produce acetic acid from CO2 by chemical catalysis. This involves three separate sub-processes. First methanol (CH3OH) is produced by simple hydrogenation of CO2:

CO2 + 3 H2 → CH3OH + H2O

Carbon monoxide (CO) is produced from CO2 by electrolysis:

2 CO2 → 2 CO + O2

Finally methanol and carbon monoxide react to form acetic acid:

CH3OH + CO → CH3COOH

Biocatalytic production of acetic acid from CO2 involves an ancient group of bacteria known as acetogenic bacteria or simply “acetogens”. Acetogenic bacteria live in low-oxygen or oxygen-free (anaerobic) environments such as sediments where they take up CO2 and hydrogen gas (H2) from their surroundings to produce acetic acid. In the course of this biochemical process, the acetogens manage to extract a sliver of metabolic energy that they can then use for growth. It is possible to recreate this process in a bioreactor by simply feeding acetogenic bacteria pure CO2 and hydrogen gas. This process is known as syngas fermentation. I know of at least one company––LanzaTech––that has commercialized the syngas fermentation process. LanzaTech takes CO2 and carbon monoxide from industrial exhaust gas and feeds it to acetogenic bacteria, which then produce a number of different chemicals including acetic acid, ethanol , and butanol.

Recently a new form of acetogenic bacterium has been discovered. These acetogens can grow on submerged electrodes inside an electrolytic chamber and manage to harvest electrical energy directly from the electrode to produce acetic acid from CO2. These so-called electrotrophic (“electricity-eating”) acetogens, therefore, do not require an external source of hydrogen gas but instead use the electric energy from the electrode to split water and thereby extract the hydrogen themselves. Producing acetic acid this way has the benefit of avoiding the need for large volumes of highly explosive hydrogen gas. So far I am unaware of any commercial production of acetic acid using electrotrophic acetogens.

This little thought experiment needs to be taken with a generous pinch of salt. Nevertheless, these are compelling numbers and a good starting point for a more rigorous analysis. It seems entirely reasonable that mycoprotein produced from acetic acid could be scaled up with already existing technology to meet a significant portion of future food demand in a scenario where conventional food production is severely disrupted. But as always the key questions remain: how quickly could it be accomplished and what would it ultimately cost?

(If you want to know more about edible microbes in general, you can check out my recent review article in the journal Food Security––no subscription required.)