ACIDULATION

This is a process of adding food that contains acid, such as fruit juice, tomatoes, or vinegar, to preserve or tenderize what you're cooking.
The book illustrates both acidulating with lime juice to help a peeled avocado keep its green color, and adding canned tomatoes to a stew to help tenderize the meat. 
Adding the tomatoes is shown below from the book.
All the steps in searing meat are the same ones that you would use in preparation for braising the meat. It only takes some liquid that contains acid and slow cooking to break down the fibers of the meat to braise it. Don't panic! Tomato juice has plenty of acid to do the job this time.  Canned whole tomatoes are excellent for this type of cooking. Drain the excess juices into a container, straining them past the lid of the can, or using your hand, then, pour out the whole tomatoes and rough cut them on a chopping surface.

Using the knife blade for a spatula, put the chopped tomatoes into the casserole pan.

Preheat the oven to 325o Fahrenheit for 10 minutes before putting the casserole in. While oven is heating, bring the flame proof casserole to a boil on the stove then turn it lower until time to place it in the oven.

Are you ready to place an order?