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Genetically Modified Cheese… Is Nothing Safe? At the Boundaries of the GMO Controversy

The views expressed are those of the author and are not necessarily those of Scientific American.

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A couple of years ago, my fiancée and I wanted to try to make some home-made mozzarella cheese, but ran into a problem. In order to turn milk into cheese, you have to add a substance called “rennet,” which causes the milk to coagulate, allowing you to separate the curd (mostly fats and hydrophobic proteins) from the whey (the water and soluble stuff). So what’s the problem? Rennet is not that tough to find, and it’s provided in most cheese-making kits you can buy (this is the one we were using). The problem: my fiancée is vegetarian, and the usual source of rennet is the lining of calf stomachs.


The part of rennet that’s most important for this process is called “chymosin,” which is an enzyme called a protease, whose function is to break down other proteins. In baby cows, chymosin is needed to break down the proteins in mother’s milk, and that’s why their stomachs are such an abundant source. Unfortunately, this also means we have to kill baby cows to make cheese, which is problematic for many reasons, not least of which is the fact that vegetarians don’t want any part of that.

Wouldn't you rather get your rennet from a bacterium instead of this little guy? (click for source)

The good news is that there are non-animal sources of proteases that are somewhat similar to chymosin. In fact, the rennet in the cheese-making kit we found is extracted form a fungus called Rhizomucor miehei. The bad news is, those enzymes aren’t quite the same as calf chymosin. They work in a similar way to coagulate milk, but the products of those enzymatic reactions are different, and could lead to different flavor profiles, and different microbial communities that colonize the aged cheese (which could further effect flavor). This isn’t a problem for people messing around with making cheese at home (the cheese from the kit was delicious btw), but inconsistency in flavor is a major concern for large-scale cheese producers.

Enter genetically modified organisms: it’s fairly trivial to make a bacterium or yeast cell that makes boatloads of chymosin – the exact same protein that’s found in the stomachs of calves – without all of the fuss and bother attendant with raising and killing cows. This process is also much more controllable and returns a more consistent product than processing from an animal source, meaning that cheese-makers can expect very little variation in their process. In fact, chymosin produced by E. coli was the first of enzyme made with recombinant DNA technology approved for use in food… all the way back in 1991.

So here’s my question: would opponents of GMO technology object to eating cheese made in this way? Avoiding it might be hard – between 80-90% of hard cheese produced in the US is made with recombinant chymosin. And what about companies like Whole Foods that are moving to label all of their products that contain GMOs, or states that are passing laws to do the same? Most regulatory agencies don’t consider chymosin an ingredient. And in any case, purified chymosin from E. coli is chemically indistinguishable from that taken from calves. And the problem goes beyond cheese, the FDA has approved over 30 recombinant enzymes for use in food production, including α-amylase, which is used in the production of almost all glucose or fructose syrups.

Groups like the non-gmo project reject the use of these enzymes, but go even further. Bafflingly, they even oppose the use of recombinant proteins to make small molecule compounds like citric acid, claiming they pose “GMO risk.” This term is meaningless – are they saying a chemical compound can somehow have memory of where it came from like the water sold as homeopathy?

When anti-GMO advocates deny the scientific consensus around crops like Bt-corn, it’s frustrating, but still somewhat understandable. Putting foreign genes in plants so they produce a pesticide sounds scary if you don’t understand genetics and the central dogma (which I admit, is not the easiest thing to wrap your head around). Even if you have some idea, you could be forgiven for being wary of a plant that’s making something from a bacterium. But the objection to using purified proteins, or even chemical compounds, that are 100% identical to that from other sources, just because it’s being made in a lab demonstrates the rank ignorance that characterizes the professional anti-GMO movement.

Kevin Bonham About the Author: Kevin Bonham is a Curriculum Fellow in the Microbiology and Immunobiology department at Harvard Medical school. He received his PhD from Harvard, where he studied how the cells of the immune system detect the presence of infectious microbes. Find him on Google+, Reddit. Follow on Twitter @Kevbonham.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. singing flea 1:18 pm 06/9/2014

    Apparently vegetarians who want to make their own cheese are not buying their milk at the store. In fact any vegetarian that buys milk or cheese that is commercially produced is contributing to the slaughter of millions of male calves because the dairy farmers don’t want to waste their mothers milk on them, but this moral dilemma only applies to people who are vegetarians because of ethical reasons. I would venture to say the majority of vegetarians choose to eat plant materials because of the health benefits. When I read statements like, ” Putting foreign genes in plants so they produce a pesticide sounds scary if you don’t understand genetics and the central dogma (which I admit, is not the easiest thing to wrap your head around).”, I have to wonder whether they understand the science behind pesticides. The moral issue becomes whether you put the toxic chemicals that insects won’t eat on the outside or the inside of the produce. One thing is for certain, micro biologists have no monopoly on common sense.

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  2. 2. mem from somerville 2:38 pm 06/9/2014

    Should we also tell them about the gene swapping across cheese-making fungal species, or should we let them find out about that on their own?

    I’m pretty sure this is illegal in the EU. Sssshhhhh…..

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  3. 3. greenhome123 4:36 pm 06/9/2014

    I heard they also have some GMO beer yeast coming out soon, which will produce beer with better head retention (not exactly my idea of a desirable trait), and some wine yeast that allows for two step fermentation process to be done in one step (this sounds a little more useful). I do think it is important that new bacteria or yeast created in a lab through genetic engineering, radiation, or other method, should be tested through animal safety studies before being allowed to be used in production of food for humans. But, I don’t see any problem with their use as long as safety studies conducted by 3rd party or government agency have shown that they do not produce any toxins or cause harm to animals the environment. Nevertheless, similar to how I choose to side with the clean energy movement (with its many flaws) instead of fossil fuel industry/climate change denier movement, I also tend to side with the anti-GMO movement rather than the Roundup Ready/overuse of fertilizer/monoculture movement. That being said I still think GMOs have a lot of potential for good in things like use of less insecticide/fungicide, drought tolerance, and producing bigger, faster/efficiently growing, more nutritious food.

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  4. 4. jimbobobie 4:39 pm 06/9/2014

    I’m not personally all that averse to the whole gmo thing. I’m almost 70 years old so there’s not that much time left for stuff to affect me. All the same, when I hear “scientists” pooh-pooh the concerns of anti-gmo folks, I am reminded of the great boon to our health that margarine was supposed to be, or the marvel of DDT, not to mention the safety of nuclear reactors or the usefulness of kudzu as a ground cover and that’s just the beginning. People are right to be concerned. As the tediously smug Donald Rumsfeld found out to his dismay, it’s the UNKNOWN UNKNOWNS you have to watch out for.

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  5. 5. greenhome123 4:40 pm 06/9/2014

    I meant overuse of herbicide, not fertilizer :-)

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  6. 6. Kevbonham 9:40 pm 06/9/2014

    @singing flea – There are all sorts of reasons for being vegetarian, health, morals, the environment. We typically try to get our cheese from small local farms. I doubt that most of the people freaked out by pesticides actually understand the science of pesticides. You don’t have to understand something to be afraid of it though.

    @mem – no, we shouldn’t :-)

    @greenhome – A good head on beer is an amazing thing, but it takes some getting used to. I was skeptical at first, but now I love it. And I agree 100% – safety testing for new strains (of plants or microbes), that are going to be part of people’s diets is a great idea.

    The trouble, as you allude to in your comment, is that there’s a untrue equivalence drawn between GE crops and industrial agriculture. Yes, there are ways that agribusiness can exploit GE tech for unsustainable purposes, but there are also ways that scientists and small farmers could exploit GE for increasing yields, decreasing water use and pesticide use etc. What we need to fight is unsustainable agriculture, whether it’s GE or organic. And we need to promote sustainable farming, whatever technology or practice promotes it best.

    @Jimbobobie – I guess one benefit of this whole anti-GMO crusade is that a crap ton of safety testing has been done. You’re 100% right to be cautious, and as I said above, I’m all for continued safety testing, especially of new strains. But there’s no good reason to dismiss all uses of GE out of hand, or to treat the products of GE as a monolith. Every GE strain is different, and there’s no reason that the safety or harm from one strain has anything to do with that of any other.

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  7. 7. KeithReding 9:54 pm 06/9/2014

    Nice article. The same argument is true for organic pesticides. Spinosad produced by fungal fermentation is allowed but not if it is chemically synthesized. It is the same exact compound. Pyrethrin is another example. Extracted from Chrysanthemum is fine but not if it is chemically synthesized.

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  8. 8. singing flea 11:40 pm 06/9/2014

    I don’t see a problem with using GMO technology for feeding the masses. If it wasn’t for technology we couldn’t sustain the population we have today. The problem is that the scientists that are doing the research are employed by corporations that have a track record of being self serving, and morally bankrupt. They own the scientists and management will only release or share with those scientists and the general public what their attorneys and accountants allow. Most research scientists in the business only work on a small part of the research and don’t get to look at the whole picture anymore. Their only interest is their salary and bonuses.

    For reasons that are obvious, the companies doing the research and the companies using the technology refuse to tell the consumer what they are doing to the food and what chemicals are introduced in the food that are not natural. As long as I am prevented from knowing what they are selling me, I prefer to take a caveat emptor decision and just say no to all of it whenever I am given a choice. Unfortunately, politics is working the courts and politicians to prevent me from even trying to get that information. I don’t trust the entire industry, and their own policies are the reason why.

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  9. 9. ScienceHealth 9:48 am 06/10/2014

    People have been making fresh cheese without rennet or GMOs for thousands of years.

    Here’s a recipe for Panir, as it’s called in India:
    Bring whole milk to a boil and add fresh yogurt.
    Keep stirring and adding yogurt while it boils, until the milk solids separate and a faintly cloudy, not milky, whey forms. Strain the whey through a muslin cloth. Squeeze the cloth to draw out all liquid and place the panir (in the cloth) under a heavy weight for a few hours. A chunky brick of panir will be formed. Dice into cubes for use, or crumble for use in recipes.

    In America, lemon juice is often substituted for yogurt but it produces a rubbery cheese that’s not as digestible or healthy.

    If you want to live a healthy and long life, it would be good to avoid all GMOs or food produced using GMO processes.
    Maharishi Mahesh Yogi (of TM fame) said the followoing about genetic engineering and the sequential flow of Natural Law…

    “Sequential evolution is the eternal flow of evolution… It is the sequential evolution of the holistic value of Natural Law. Starting from the holistic value of infinity in the unmanifest, it unfolds sequentially to eventually be the holistic value of the manifest. The sequence that is free from any problems, free from any inhibition of the evolutionary process; that is a sequence of evolution.
    “It is very, very important—genetic engineering disturbs this sequence. It disturbs the sequence. That is why it is unnatural. Unnatural means disallowing the natural process of renewal of life–navo navo bhavati.
    “Obstruction in evolution is obviously and clearly damaging to life. That’s how life gets problems and disease; balance is broken. Sequential evolution is deprived of its natural, direct flow of evolution. Interference in the sequential progression of life is damaging to life.”

    Take care.

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  10. 10. ScienceHealth 9:58 am 06/10/2014

    Your fiance is wise to be vegetarian. If you want to live as happily and as long as she, you would be wise to follow suit. Eating animals is slow suicide.

    Before animals are killed they are actually aware of what’s going to happen to them. They secret adrenaline and other toxic chemicals that you consume when you eat them. Small wonder that eating meat results in early heart disease, stroke, cancer, osteoporosis, kidney disease, diabetes, etc.

    Then there are other reasons to avoid meat (GMOs, drug resistant bacteria from overuse of antibiotics, grow hormones, global warming, water pollution, grain shortages).

    Some call for more humane slaughter of animals, but what can be humane about killing animals against their will? It’s no longer the ice age! We have a choice, so there is no morally justifiable reason to eat animals.

    The myth of ‘humane meat’…

    U.S. meat widely contaminated with drug-resistant bacteria

    Good luck and a long life to you.

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  11. 11. Kevbonham 3:09 pm 06/10/2014

    @ Keith – That’s fascinating, I had no idea.

    @ sf – Two things: 1) I agree that we should take results of industry funded studies with a grain of salt. However, scientific results from industry-funded sources should not be dismissed out of hand. Most scientists, even those working for or taking money from industry are honest, hard working people. They have obvious conflicts of interest, and that should increase skepticism of their results, but not negate them entirely. 2) There are plenty of non-industry funded work on the safety of GMOs that largely reach the same conclusions. Take a look at “Genera” ( for examples.

    @ SH – Thanks for the recipe… I love panir, and may give this a try! However, panir is different from the sorts of cheese I’m taking about. There’s probably something about the acidity of the yoghurt or lemon juice that induces coagulation, but this is a different process and as such the cheese has different flavors.

    I also have to push back against your yogi – that statement is meaningless. Just because something is “natural,” that does not make it good, and just because something is “unnatural,” that does not make it bad. In one sense, all agriculture is unnatural – humans have modified plants for ten thousand years. In another sense, humans have evolved to use our enormous brains to do amazing things, therefore using genetic engineering is just an extension of our own evolution.

    People use this naturalistic fallacy to justify their own preconceptions, it has nothing to do with reality.

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  12. 12. cautiousguy 9:49 pm 06/12/2014

    There is a huge difference between inserting a gene into a bacterium and tricking it into making lots of protein from that gene that is then harvested for a specific product, and inserting foreign genes into food crops. BT crops contain insecticide in every cell of the plant. It cannot be washed off. Round-up ready crops save the farmer some cost for weed control for a few years, until the weeds develop resistance and weed control then requires ever-increasing amounts of round-up as well as other, more toxic herbicides. Furthermore, there is no way to prevent these added traits from migrating into wild related species of plants, with totally unknown consequences.

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