This is the Simple Secret to Tender Pinoy-style Beef Steak
Soy sauce mixed with calamansi juice is a common dipping sauce but when made into a marinade, as you would when making beef steak or bistek, it transforms the simple condiment into a delicious dish.
But there is more to the marinade ingredients than just its complementary flavors. Beef is notoriously tough when overcooked, even sliced as thinly as it is for bistek. That's where the marinade comes in. Calamansi juice, or any acidic ingredient such as other citrus juices and vinegar, is essential in tenderizing the beef. That's because the acid (in this case, calamansi juice) breaks down the connective tissues of the meat (the beef) transforming it into tender cuts.
However, marination can work against you if the meat marinates for far too long. Any acidic ingredient in a marinade "cooks" the meat, thus making an otherwise flavorful and tenderizing marinade into one that "overcooks" it unnecessarily and creating meat that, while tender, is also chalky in texture.
So what you want to do is this: marinate the beef just long enough to let its flavors penetrate while the calamansi juice tenderizes the beef without overdoing it.
Keep this in mind when next you use calamansi in your marinade, and it will be a delicious and tender meat you'll bite into every time.