Eye of round steaks are on the lean side, which means they aren't quite as tender, juicy and flavorful as pricier, better marbled cuts. While marinating is more effective at imparting flavor than at tenderizing beef, using an acidic marinade base with certain enzymes -- like pineapple juice, for example -- does offer some tenderizing benefits. However, these effects peak after just a few hours, after which time they start to make the steak mushy and negatively affect the texture, taste and color of the meat.
Clean and dry a large glass, ceramic, plastic or stainless steel baking dish large enough to hold the eye of round steak and marinade. Do not use reactive metals like copper and aluminum, which can impart a metallic taste and color.
Pour about 1/4 cup of pineapple juice per pound of steak into the marinating vessel to comprise both the acidic component and sugar all marinades should contain.
Add an equal amount of mild cooking oil, such as canola, vegetable or safflower oil, into the pineapple juice. Oils comprise another essential marinade component and help distribute the flavors over the food.
Combine the pineapple juice and oil with about half as much soy sauce as the other individual liquid ingredients. The soy sauce supplies salt to add depth of flavor and help the eye of round steak better retain moisture.
Season the marinade with a little additional salt and some freshly cracked black pepper to taste. Add a bit of rosemary or other complementary herbs or spices if desired.
Lay the eye of round steak in the dish with the marinade. Cover the dish tightly with plastic wrap or the cover. Put the marinating meat into the refrigerator.
Turn over the eye of round steak after 30 minutes to 1 hour of soaking in the refrigerator. Cover the dish back up and marinate the other side of the steak for another 30 minutes to an hour.
Remove the eye of round steak from the marinade and let the excess drip off. Discard the marinade, as it has been contaminated by raw beef. Or, to use it as a sauce, bring the liquid to a full boil for at least 5 minutes to kill off bacteria and render it safe for consumption.