The false claim that US President Biden’s Climate Change Plan would lead to hamburger rationing has provided a predictably useful attack line for his opponents. But underlying this further manifestation of the polarisation of US politics, there is a real issue – producing the food we eat does produce substantial greenhouse gas emissions, and a disproportionate amount of these emissions come from eating the meat of ruminants like cattle and sheep.
According to a recent study, US emissions from the food system amount to 5 kg a person a day, and 47% of this comes from red meat. Halving the consumption of animal products by would reduce the USA’s greenhouse gas emissions by about 200 million tonnes of CO2 equivalent, a bit more than 3% of the total value. In the UK, the official Climate Change Committee recommends that red meat consumption should fall by 20% by 2050, as part of the trajectory towards net zero greenhouse gas emissions by 2050, with a 50% decrease necessary if progress isn’t fast enough in other areas. At the upper end of the range possibilities, a complete global adoption of completely animal-free – vegan – diets has been estimated to reduce total global greenhouse gas emissions by 14%.
The political reaction to the false story about Biden’s climate change plan illustrates why a global adoption of veganism isn’t likely to happen any time soon, whatever its climate and other advantages might be. But we should be trying to reduce meat consumption, and it’s worth asking whether the development of better meat substitutes might be part of the solution. We are already seeing “plant-based” burgers in the supermarkets and fast food outlets, while more futuristically there is excitement about using tissue culture techniques to produce in vitro, artificial or lab-grown meat. Is it possible that we can use technology to keep the pleasure of eating meat while avoiding its downsides?
I think that simulated meat has huge potential – but that this is more likely to come from the evolution of the currently relatively low-tech meat substitutes rather than the development of complex tissue engineering approaches to cultured meat . As always, economics is going to determine the difference between what’s possible in principle and what is actually likely to happen. But I wonder whether relatively small investments in the food science of making meat substitutes could yield real dividends.
Why is eating meat important to people? It’s worth distinguishing three reasons. Firstly, meat does provide an excellent source of nutrients (though with potential adverse health effects if eaten to excess). Secondly, It’s a source of sensual pleasure, with a huge accumulated store of knowledge and technique about how to process and cook it to produce the most delicious results. Finally, eating meat is freighted with cultural, religious and historical significance. What kind of meat one’s community eats (or indeed, if it it eats meat at all), when families eat or don’t eat particular meats, all of these have deep historical roots. In many societies access to abundant meat is a potent signifier of prosperity and success, both at the personal and national level. It’s these factors that make calls for people to change their diets so political sensitive to this day.
So how is it realistic to imagine replacing meat with a synthetic substitute? The first issue is easy – replacing meat with foods of plant origin of equivalent nutritional quality is straightforward. The third issue is much harder – cultural change is difficult, and some obvious ways of eliminating meat run into cultural problems. A well-known vegetarian cookbook of my youth was called “Not just a load of old lentils” – this was a telling, but not entirely successful attempt to counteract an unhelpful stereotype head-on. So perhaps the focus should be on the second issue. If we can produce convincing simulations of meat that satisfy the sensual aspects and fit into the overall cultural preconceptions of what a “proper” meal looks like – in the USA or the UK, burger and fries, or a roast rib of beef – maybe we can meet the cultural issue halfway.
So what is meat, and how can we reproduce it? Lean meat consists of about 75% water, 20% protein and 3% fat. If it was just a question of reproducing the components, synthetic meat would be easy. An appropriate mixture of, say, wheat protein and pea protein (a mixture is needed to get all the necessary amino acids), some vegetable oil, and some trace minerals and vitamins, dispersed in water would provide all the nutrition that meat does. This would be fairly tasteless, of course – but given the well developed modern science of artificial flavours and aromas, we could fairly easily reproduce a convincing meaty broth.
But this, of course, misses out the vital importance of texture. Meat has a complex, hierarchical structure, and the experience of eating it reflects the way that structure is broken down in the mouth and the time profile of the flavours and textures it releases. Meat is made from animal muscle tissue, which develops to best serve what that particular muscle needs to do for the animal in its life. The cells in muscle are elongated to make fibres; the fibres bundle together to create the grain that’s familiar when we cut meat, but they also need to incorporate the connective tissue that allows the muscle to exert forces on the animal’s bones, and the blood-carrying vascular system that conveys oxygen and nutrients to the working muscle fibres. All of this influences the properties of the tissue when it becomes meat. The connective tissue is dominated by the protein material collagen, which consists of long molecules tightly bound together in triple helices.
Muscles that do a lot of work – like the lower leg muscles that make up the beef cuts known as shin or leg – have a lot of connective tissue. These cuts of meat are very tough, but after long cooking at low temperatures the collagen breaks down; the triple helices come apart, and the separated long molecules give a silky texture to the gravy, enhanced by the partial reformation of the helical junctions as it cools. In muscles that do less work – like the underside of the loin that forms the fillet in beef – there is much less connective tissue, and the meat is very tender even without long cooking.
High temperature grilling creates meaty flavours through a number of complex chemical reactions known as Maillard reactions, which are enhanced in the presence of carbohydrates in the flour and sugar that are used for barbecue marinades. Other flavours are fat soluble, carried in the fat cells characteristic of meat from well-fed animals that develop “marbling” of fat layers in the lean muscle. All of these characteristics are developed in the animal reflecting the life it leads before slaughter, and are developed further after butchering, storage and cooking.
In “cultured” meat, individual precursor cells derived from an animal are grown in a suitable medium, using a “scaffold” to help the cells organise to form something resembling natural muscle tissue. There a a couple of key technical issues with this. The first is the need to provide the right growth medium for the cells, to provide an energy source, other nutrients, and the growth factors that simulate the chemical communications between cells in whole organisms.
In the cell culture methods that have been developed for biomedical applications, the starting point for these growth media has been sera extracted from animal sources like cows. These are expensive – and obviously can’t produce an animal free product. Serum free growth media have been developed but are expensive, and optimising, scaling up and reducing the cost of these represent key barriers to be overcome to make “cultured meat” viable.
The second issue is reproducing the vasculature of real tissue, the network of capillaries that conveys nutrients to the cells. It’s this that makes it much easier to grow a thin layer of cells than to make a thick, steak-like piece. Hence current proofs of principle of cultured meat are more likely to produce mince meat for burgers rather than whole cuts.
I think there is a more fundamental problem in making the transition from cells, to tissue, to meat. One can make a three dimensional array of cells using a “scaffold” – a network of some kind of biopolymer that the cells can attach to and which guides their growth in the way that a surface does in a thin layer. But we know that the growth of cells is influenced strongly by the mechanical stimuli they are exposed to. This is obvious at the macroscopic scale – muscles that do more work, like leg muscles, grow in a different way that ones that do less – hence the difference between shin of beef and fillet steak. I find it difficult to see how, at scale, one could reproduce these effects in cell culture in a way that produces something that looks more like a textured piece of meat rather than a vaguely meaty mush.
I think there is a simpler approach, which builds on the existing plant-based substitutes for meat already available in the supermarket. Start with a careful study of the hierarchical structures of various meats, at scales from the micron to the millimetre, before and after cooking. Isolate the key factors in the structure that produce a particular hedonic response – e.g. the size and dispersion of the fat particles, and their physical state; the arrangement of protein fibres, the disposition of tougher fibres of connective tissue, the viscoelastic properties of the liquid matrix and so on. Simulate these structures using plant derived materials – proteins, fats, gels with different viscoelastic properties to simulate connective tissue, and appropriate liquid matrices, devising processing routes that use physical processes like gelation and phase separation to yield the right hierarchical structure in a scalable way. Incorporate synthetic flavours and aromas in controlled release systems localised in different parts of the structure. All this is a development and refinement of existing food technology.
At the moment, attempting something like this, we have start-ups like Impossible Burger and Beyond Meat, with new ideas and some distinct intellectual property. There are established food multinationals, like Unilever, moving in with their depth of experience in branding, distribution and deep food science expertise. We already have products, many of which are quite acceptable in the limited market niches they are aiming at (typically minced meat for burgers and sauces). We need to move now to higher value and more sophisticated products, closer to whole cuts of meat. To do this we need some more basic food science research, drawing on the wide academic base in the life sciences, and integrating this with the chemical engineering for making soft matter systems with complex heterogenous structures at scale, often by non-equilibrium self-assembly processes.
Food science is currently rather an unfashionable area, with little funding and few institutions focusing on it (for example, the UK’s former national Institute of Food Research in Norwich has pivoted away from classical food science to study the effect of the microbiome on human health). But I think the case for doing this is compelling. The strong recent rise in veganism and vegetarianism creates a large and growing market. But it does need public investment, because I don’t think intellectual property in this area will be very easy to defend. For this reason, large R&D investments by individual companies alone may be difficult to justify. Instead we need consortia bringing together multinationals like Unilever and players further downstream in the supply chain, like the manufacturers of ready meals and suppliers to fast food outlets, together with a relatively modest increase in public sector applied research. Food science may not be as glamorous as a new approach to nuclear fusion, but maybe turn out to be just as important in the fight against climate change.
. See also this interesting article by Alex Smith and Saloni Shah – The Government Needs an Innovation Policy for Alternative Meats – which makes the case for an industrial strategy for alternative meats, but is more optimistic about the prospects for cell culture than I am.