Cellulose is the most abundant renewable carbon source on the planet. Plants capture carbon dioxide (CO₂) gas from the atmosphere and, through the magic of photosynthesis, turn it into solid, carbon-based molecules such as glucose. Plants can then turn this glucose into polymers such as starch and cellulose. Starch, abundant in corn kernels and grains of rice and wheat, are staple food sources for us humans. (Where would we be without fried rice and sourdough bread?)  The other polymer, cellulose, is even more abundant in plants because it’s structural – it’s the basis of the stalks that hold up the corn cobs and ears of wheat.

So why, other than the little benefit of keeping our plants upright, is cellulose so important? The main cause of climate change is that we rely an awful lot on fossil fuels for energy and materials. We are using carbon that has been stored in the ground for millennia, either to convert into chemicals and plastics, or to burn for energy. Instead, we should be making better use of the carbon that’s captured from the atmosphere by plants, the most abundant version of which is cellulose.

How much CO₂ is captured by plants?

Since climate change is caused by an increase in CO₂ and other greenhouse gases (GHGs) in the atmosphere, it’s important to consider how much CO₂ we emit versus how much is captured by plants.

In their last assessment, the Intergovernmental Panel on Climate Change (IPCC) reported that we humans released 59 billion tonnes of CO₂ equivalents in 2019. Our carbon budget (starting in 2020) to give us a 50% chance to keep global warming below 1.5°C is only 500 billion tonnes. As you can imagine, something has to change, and fast, or we’ll blow through that budget by 2030.

Plants, seaweeds, and other photosynthetic organisms capture CO₂ from the atmosphere and turn it into biomass. Consider that photosynthetic organisms capture an estimated 250 billion tonnes of CO₂ each year and store it as biomass. This is known as net primary production (NPP). Bear in mind that this number is sometimes reported as 70 billion tonnes of carbon (rather than CO₂) – CO₂ is 27% carbon, so this amounts to the same thing. Other estimates for NPP are a little higher than this: 100 billion tonnes of carbon, which equates to 370 billion tonnes of CO₂ each year.

This equals about 1% of the world’s known reserves of fossil fuels (coal, gas, and oil), or 10 times the world’s current annual energy consumption. – Bionumbers, Harvard

The point here is that plants capture several times more CO₂ each year than we humans emit. This is why maintaining and replenishing our forests is so critical to mitigating climate change. Eating red meat is the biggest threat to our forests and therefore the planet, by the way.

We need to make better use of all that carbon that’s captured by plants instead of using fossil fuels. We already make use of the starchy edible parts by eating them, but what about the more abundant portion – all that cellulose?

Making better use of cellulose

One of the most familiar applications for cellulose is to convert it into paper and cardboard, which is then efficient to recycle. Paper products have good standing in the circular economy being bio-based but also recyclable. Other examples where cellulose is used sustainably include:

Cellulose-based building materials

Wood, when responsibly harvested, is a more sustainable alternative to steel and concrete, which are each responsible for a whopping 7% of global GHG emissions. 

Straw bales can be used to build houses in dry climates, or at least to serve as insulation.

Hemp fibers can be integrated into concrete (we call this Hempcrete) to reduce its carbon footprint. Concrete is the most consumed material on earth, after fresh water.

Cellulose-based textiles

You’re familiar with cotton, of course – this is basically 100% cellulose. Cotton is not the most sustainable textile but it’s better than the petroleum-based synthetics. Organic cotton is a better choice for a few reasons, explained in this post that asks: How ethical is Taylor Swift merch?

Even better, we now have textiles made from regenerated cellulose, such as Tencel and Lyocell. See this GSP post on ranking of sustainable textiles for more info on these materials.

Emerging uses of cellulose for food

That still leaves a lot of cellulose that we can use. We generate a lot of agricultural waste – straw leftover from crops such as wheat and rice, corn cobs stripped of kernels, etc. – and a good amount of it is burned, releasing the CO₂ back into the atmosphere. Many scientists are working towards the conversion of cellulose into useful products – in fact, I spent a lot of my career as a scientist working towards fuel production from cellulose.

It’s hard to make the economics work for conversion of cellulose into something like jet fuel because it needs to compete with the heavily subsidized fossil fuel industry. That this is still true, in the age of climate change, is a travesty.

But it’s likely that we’ll see more applications emerging for cellulose – some of which will be in the food space. I’ll wrap up this post by sharing two examples where cellulose can be converted into food products (one is theoretical, the other is getting started).

Meat substitutes from cellulose

Quorn is a meat substitute, made from a fungus that’s grown in a fermenter, often starting from wheat starch. However, the UK-based company, Quorn Foods, recently investigated the production of their products from cellulose (e.g., wheat straw instead of grain).

Quorn is involved in research to take this to the next level: instead of using plant starch as the source of sugar for their fermentation, they want to use cellulose. Cellulose is the most abundant carbon source on the planet and there are groups all over the world working towards its conversion into useful products. [It can be sourced from] the structural parts of the plant that we don’t eat – rice and corn stalks, for example. To make food from these carbon sources would be a quantum leap towards a more sustainable planet. I’m very excited about this.

This is not a reality yet, but the potential is there, especially as the price of food increases due to the impacts of climate change on agriculture. See my GSP post on sustainability of Quorn for more detail.

Upcycled sugars from cellulose

Another UK-based enterprise, The Supplant Company, is making sugars from cellulose. On my other blog, Ethical Bargains, I recently evaluated chocolate bars made by Supplant, in collaboration with star chef Thomas Keller.

Supplant uses enzymes from fungi to convert this cellulose into shorter sugars that we are able to digest. Because the product is not a pure sugar (sucrose or glucose) but rather a mixture of sugars, oligosaccharides, and longer fibers, we metabolize them differently.

Benefits to humans include prebiotic fiber content and a lower glycemic response (15% that of glucose).

The sugars (besides coconut sugar) that went into the Thomas Keller chocolate were made from corn cobs (i.e., after the kernels are removed), making good use of what’s essentially a waste product. The process can be applied to almost any agricultural side-product that consists of mainly cellulose (e.g., oat hulls, wheat straw, corn stover, etc.) which effectively increases the food yield for these crops.

Head over to Ethical Bargains for more information on The Supplant Company’s upcycled sugars.

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