Laura, I have also been pressure cooking meat for about 15 years. Aside from general experience, my particular experiments are these:
1. First, I cut a pork tenderloin in half, seasoned and seared both halves. I cooked half in each of two electric pressure cookers at the same time. The first I set for 0 minutes on low pressure, and let the pressure release naturally (I believe that took 10-12 minutes). The second I set for 4 minutes on low pressure and quick-released the pressure. I timed the two cookers so that the tenderloin halves finished within a couple of minutes of each other. I took the temperature of each and they were virtually identical — about 145F. I let each rest for a few minutes, then sliced and served myself and 3 guests, putting some of each tenderloin half on each plate. No one could tell any difference. I’ve also done the same with chicken breast, with the same results.
2. Admittedly, that depended on the subjective judgments of my guests, so I devised a second set of experiments to measure only the moisture loss of meat under natural and quick release. (I did all of this set in my Instant Pot Ultra.) First, I measured the amount of liquid lost in the pressure cooker just using water to get a baseline. I added 500 grams of water and set the pressure cooker for 10 minutes on high pressure, with complete natural release of pressure, which took 20 minutes. The pressure cooker lost 20 grams of water (that is, I ended up with 480 grams, give or take a few grams that may have been clinging to the pot). So it lost about 4 percent of the water. I then did the same thing (500 grams of water, 10 minutes high pressure), but with quick release. In that case, the pressure cooker lost 40 grams of water, so twice as much, but still not much compared with the staring volume.
Part two was cooking meat. I chose two pieces of pork shoulder that were similar in appearance (that is, they had very little external fat and looked to have about the same amount internally) and were taken from the same shoulder piece. I cooked them plain so salt wouldn’t interfere with the transfer of liquid, over 500 grams of water on a trivet. This time I cooked them for 30 minutes. With the first, I let the pressure release naturally; with the second I quick released the pressure.
In the first cooking session (with natural release), I started with 440 grams of meat and ended up with 264 grams, or 60% of the starting weight. I ended up with 625 grams of liquid, or 25% more than the starting weight. After weighing the meat and liquid, I took the temperature of the meat in a few places and got readings of 190F to 194F.
In the second (with quick release) I started with 425 grams of meat and ended up with 272 grams, or about 64% of the starting weight. I ended up with 590 grams of liquid. To compensate for the extra 20 grams I presumably lost due to quick release, I added that for a total of 610 grams, or 22% more than the starting weight. The ending temperature of the meat was comparable to the first batch.
So, here’s my conclusion. I assume that the change in weight after cooking is due to liquid leaving the meat, and to fat rendering out. Quick release DID NOT cause more liquid to leave the meat (as a percentage of starting weight); in fact, slightly less did. Further, assuming that the increase in liquid in the pot was due to liquid leaving the meat and fat rendering out, again, there was more liquid after natural release than quick release. Obviously I want to repeat these experiments, but my preliminary conclusion is clear — quick release on its own does not dry out meat.
(You will notice that I didn’t talk about toughness, since that’s difficult if not impossible to measure by objective standards. I will say that the day after cooking when I shredded the meat, I found it impossible to tell which piece was from which batch. But that’s subjective.)
I know that many people (you and Greg included) claim that in their experience, quick release dries out meat. Obviously I can’t account for your personal experience, but I haven’t read of anyone doing similar experiments and getting vastly different results. Until I do (or if I get vastly different results when I repeat my experiments), I’m standing by my statement.
(I got the language and information about protein matrices from the book “Ingredient” by Ali Bouzari, a chef with a PhD in food biochemistry. He actually uses the term “protein web”, so I guess I misspoke slightly.)
