Do you enjoy cheese? On pizza? In a Greek salad? As a crumbly bit of Stilton cheese served with a glass of port?
I love cheese. Cheese was my son's first word. "Chee!" he yells when we enter the cheese section of our favorite grocery store.
Cheese is a pretty cool food. As a microbiologist, I'm fascinated with the way it is made. First we take a whole lot of milk. Milk is rich in a protein called casein, which is dissolved in the fluid of the milk. If you treat milk with rennet, the rennet cuts up the casein protein into smaller chunks that expose hydrophobic parts of the protein. So it precipitates. That is, it comes out of solution and sinks to the bottom of the solution. Cheesemakers call this precipitate curds (and the remaining liquid is called whey). This beginning bit is the same for almost every cheese on the market (yes, even that awful American cheese). The curds are the raw ingredient that all cheese is made from.
Back in the day, rennet came from calf stomachs. (If you want to get an enzyme that breaks down milk products, what better place to look than something that eats milk?). It was a byproduct of veal production. But as you might imagine, getting rennet from calf stomachs is rather expensive (if also a little grisly). So people started to look for substitutes. Most of the substitutes don't work as efficiently or as rapidly as the rennet enzymes from calf stomach preparations, so in the early 1980's, some molecular biologists cloned the rennet gene and expressed it in yeast. Egads! Now, you can make cheese without having to chop up calf stomachs (or calves)! As of 1999, more than 60% of cheese made in the U.S. used this genetically engineered rennet. No doubt by now it is considerably more.
So shouldn't we be excited? This is a win/win/win situation. We get cheaper cheese. Nobody needs to chop up calves. The yeast used to produce the enzyme has been safely used to make bread, beer and wine for millenia. Safe! Cheap! Calf friendly! But due to the unpleasant public relations issue of being a genetically-modified product (cue thunder), most folks keep this a guarded secret. Take this home cheesemaking website:
Liquid Chymostar Classic - 2 oz. This is a high quality rennet, originating from animal sources, but containing no animal product.Indeed. This has to be recombinant, but they are careful not to say so. Why not be proud? Well, perhaps to prevent the fearmongers from stopping by. So the next time you're enjoying a pizza, know that it's very likely that no calves were carved up to produce your cheese. That it was produced in a manner that is safe. And that you have modern molecular biology to thank for it.