The Chinese get beef so tender through a process that is called velveting, which is a technique that uses baking soda to raise the pH of the meat, which breaks down the meat's proteins, followed by rinsing of the beef and marinating the beef in some soy sauce, rice wine, egg white and then also a quick par fry in oil or water to seal in moisture and then they use a final stir fry.
Also slicing properly against the grain in the beef also shortens the fibers for tenderness of the beef.
The secret ingredient in getting beef so tender as well as making tender stir fry beef is a Chinese technique which is known as velveting the meat, that uses a mix of oil and cornstarch and sometimes even some egg whites or baking soda.
To make great stir fry beef, you should use the Chinese technique of using a mix of the oil and cornstarch and even baking soda or egg whites, which tenderizes the beef and creates a protective layer, which keeps the beef moist and silky when it's cooked quickly in a hot wok.
The key when making great stir fry beef is the coating and tenderizing process before cooking the stir fry beef and not just a single ingredient in the sauce that is used.
The baking soda is what breaks down the meat fibers in the beef for extreme tenderness, although to avoid a soapy taste you should use it sparingly and use only around 1/2 tsp per lb.
Egg whites in the stir fry beef seal in moisture and creates a nice silky texture that is often used with cornstarch.
The cornstarch for the stir fry beef forms a protective barrier, which locks in moisture and gives it a smooth and velvety finish.
And the oil is added to the stir fry beef marinade to help with the process of velveting and prevent sticking.
Soy sauce, garlic, ginger and oyster sauce is also essential for flavor of the stir fry beef, but velveting the beef first is the truly secret technique that restaurants use for making exceptional and tender stir fry beef.