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For the Thanksgiving feast this year I was responsible for the turkey, so I had the opportunity to brine a turkey again.

Turkey. Representative of typical results.

I was thinking about the whole process this year, and was wondering if osmotic pressure had much of a role in getting the additional water into the turkey meat. Osmotic pressure develops when solutions of different concentrations are separated by a semi-permeable membrane.



The movement of solute (in this case H₂0) favors moving from the less concentrated to the more concentrated solution.

This is where we start to run in to problems with the assumption that osmotic pressure is the mechanism behind turkey brining. We know from the brine recipe that there is about 1/2 cup of salt per gallon of water, which results in a 1.12 M solution. For comparison, physiological saline (0.9% NaCl) has a molarity of 0.156 M. If we assume turkeys have the same salt concentration as people, that leaves a difference between the brine and the turkey meat of 0.964 M. The big problem here is the direction of the offset. The higher concentration is in the brine, not the turkey meat. The pressure is in the wrong direction to force more H₂0 into the meat.

It turns out I’m not the first to ponder this question, and there is an alternate hypothesis.

The real answer has to do with the shape of proteins. In their natural state, the muscle cells are tightly bound within their protein sheaths—this doesn’t leave much room for excess water to collect in the meat.

But as anyone who has ever made sausages or cured meats knows, salt has a powerful effect on muscles. A 6% solution of salt will effectively denature (read: unravel) the proteins that make up the sheath around the muscle bundles. In this loosened, denatured state, you can now fit more water into those muscles than in their natural state. Even better, the denatured proteins in the sheaths contract far less as they cook, therefore squeezing out much less moisture.

So it turns out that denaturing proteins has a much bigger role in the effect of brining turkey than osmotic pressure.

I don’t think the knowledge will help you make a better turkey next year, but if you need something new to talk about at the Thanksgiving table, it might due the trick. If the guests fall asleep you can always blame the tryptophan.