What is the relationship between rate of cooling and crystal size?

As the rate of cooling increases, crystal size decreases. This means that something which cools very quickly will have smaller crystal formations, and something which cools slowly will have larger crystal formations. This is easily seen in igneous rock, which may cool at variable rates. Sometimes, larger crystals are trapped among lots of smaller crystals, showing that parts of an older, slow-cooled rock were broken up and mixed in with magma which has cooled quickly.

We can also see this principle in our very own homes! Sometimes when we put meat into the freezer to keep and then thaw it out, lots of fluid is lost during the thaw process. This can make a mess and even make the meat dry after cooking. Why might that be? It all has to do with the rate of cooling! When larger pieces of meat, like a roast, are placed directly into the freezer from room temperature, they do not cool at an even rate. This slow process of freezing-- sort of from the outside inward-- creates large ice crystals in the meat. When we take it out to thaw, those ice crystals melt, leaving behind big holes in the cellular structure. It's almost like the meat has been poked through with an icicle! Because the cellular structure has been damaged, fluid is let free in the thaw process. One way we can avoid this damage is to increase the rate of freezing. Begin by putting the meat into the refrigerator so that it can cool to a low temperature (without freezing) as uniformly as possible. When it's cool all the way through, transfer it to the freezer! Because the meat is already at a very low temperature, it will freeze faster, resulting in much smaller ice crystals and less tissue damage.