Water Velveting (The Chinese restaurant secret to tender stir fried meat)
1) Beat an egg white and a tablespoon or two of vinegar in a bowl with a little corn starch (Increase proportions if you are doing a lot of meat, obviously)
2) Slice meat of choice (chicken/pork/beef) into strips or pieces.
3) Mix the meat and egg white/vinegar mixture and cover with plastic -- let it sit for 30 minutes or so.
4) Bring a pot of water to a boil. When it is boiling rapidly blanch the meat for a minute or two. You only want to cook the outside, not cook it all the way through.
5) Stir fry the meat in a hot skillet until cooked/brown as usual.
The egg white mixture acts as a meat tenderizer and blanching it seals in the moisture. The result is tender stir fried meat for your dishes. Since discovering this trick I use it every time I make stir fry now. Yes it takes an extra 5 minutes but it is so worth it.
Some sources say you can get a similar result using baking soda and water. Those sources lie!!! I tried it once with chicken and it came out horrid, the texture and flavor of the meat was not good at all.
Here is an article on water velveting if you want to read more:
https://www.seriouseats.com/2014/07/chinese-velveting-101-introduction-water-velveting.html