I have never used soda or beer for tenderizing. For me cooking meat in the crock makes it melt in plain broth or even water.

Okay, I would LOVE to go off and write out a long, long post, but I won't. I'm going to keep this very brief. Or try like hell.

Meat is made up of tiny protein strands, interwoven with a few other materials, like fat and connective fibers. When you talk about different meats you're describing the density of the protein strands and the adjoining material. "Working meat" has far more strands packed tightly and is considered "tougher." "Non-working" meat (like the meat from inside and under the rib cage or along the back of the animal) is considered more tender and has a higher fat ratio.

Now, when you cook meat it can cause a reaction in the strands. Cook it slowly and the strands will "unwind" and make the meat more tender. So, "working meat" needs to be cooked "low and slow" to get the best result. "Non-working" meat should be quickly cooked to sear the outside and seal in juices, otherwise it may seem dry and "mealy."

The additives you mentioned are all acidic in nature. BBQ sauce (especially tomato based ones), beer (fermentation), soda (citric acid), etc. They all contain acids that break down the protein bonds and help the meat to unwind and relax, making it looser, more tender. It also has the added effect of "melting" fat so it can actually make the meat lose some of it's flavor, which is why browning and/or searing can be so important.

Finally, the crockpot. This is the true "low and slow" environment. Some meats can and should be browned/seared before placing them in the crock. Especially if cooked with an acid based marinade/sauce. However, if you're cooking "au natural" or with a simple broth or water, it's not necessary. The crockpot allows cooking of the least expensive, tougher, cuts of meat, normally avoided, with a little extra time and care rendering a REALLY delicious result.

Okay, I've been geeky and wordy enough for one day. I hope that helps.

Love and light, dear ones.
Rev