The Science of Lime Marinade

Last week we shared a recipe for Bison Fajitas using lime juice to denature the meat prior to cooking. This brought up some interesting conversations at the Franklin Farmers Market about exactly what the lime juice in the recipe does to the meat. An what exactly does it mean to denature meat?

In the Bison Fajita recipe we used lime juice which is acidic (low pH) to “pre-cook” the bison without the use of heat. The lime juice contains high concentrations of natural acids such as citric acid and ascorbic acid. The pH of lime juice is about 2.5, which is more acidic than vinegar. As the lime juice diffuses into the bison, its low pH causes the proteins in the bison to denature and form protein networks. As a result, the bison becomes more opaque. As you stir the lime juice into the sliced bison you can actually see the change in appearance happen very quickly. You can “overcook” your bison with lime juice. If you leave it marinating too long it will not only make it tough.

Bison meat is mainly proteins, which look like microscopic threads under a microscope. Without heat or denaturing each protein thread kinks into a tiny ball. When you add heat or a strong acidic substance the meat the balls unravel. This is the process of denaturing.

Typically this chemical process of denaturing is only applied to fish in the process of making ceviche and not your everyday red meat. This is because beef and poultry are full of fat. In the typically cooking process heat is used to render the fat, however bison is so low in fat that we can greatly reduce the heat cooking time with amazing results.

You will notice in the Bison Fajita recipe we used both the acidic solution of lime juice and heat to denature the meat prior to cooking.

According to Cook’s Illustrated, “’Everybody just assumes marination is going to tenderize meat, so they leave it in the refrigerator for three days. It really just breaks down and becomes soft and mushy. Tenderizing comes from the way you cook it.” The reason we recommended only a quick marination in lime juice is because if you leave it too long it causes the proteins to coagulate, which leaves the meat tough or turns it to mush.

So how long is too long to marinate bison in an acidic solution? We asked Goldilocks to help us find the time that was just right. The photos below show slices of bison marinated in straight lime juice for various amounts of time.

Here is what Goldilocks found:

• 0 minutes: Bison is completely raw. Red.
• 5 minutes: Just right! Definite textural and color changes to the bison. Nicely firm on the outside, but still tender and moist in the interior.
• 10 minutes: Still just right!
• 15 minutes: Overcooked. If you can see it the edges of the meat have become completely translucent. The acid has begun breaking down the connective tissue in between the layers of the flesh, which causes it to start falling apart