Grits are a traditional American dish made from ground dried hominy (a form of specially processed corn) which is simmered until it becomes soft and creamy.
When cooked, the grits expand and absorb the cooking liquid, taking on a somewhat gelatinized consistency. Different grinds of grits are available, ranging from coarse to medium to fine. Although grits are usually white, they can be yellow as well.
The color difference is about which species of corn is used to make the hominy.
Grits possess a relatively mild flavor on their own but will take on the flavor of the cooking liquid. They're also typically flavored with salt, butter, and cheese during cooking.
A good rule of thumb when cooking grits is that they will absorb about four times their volume in liquid. Therefore, to prepare one cup of grits, you'd use four cups of water or stock, simmering for twenty to twenty-five minutes until the liquid is fully absorbed. Instant grits are also available, which cook in just a few minutes.
Grits are a popular breakfast staple in the American South, where they're served instead of potatoes. But they can be eaten at any meal, with shrimp and grits being a particularly popular recipe.
Grits = Polenta?
And now here's something you might not know: grits and polenta are not the same things. And it's not because polenta is yellow and grits are (usually) white.
As I mentioned at the top, grits are made from ground dried hominy. And the word hominy refers specifically to corn (usually a variety of corn called flint corn) that has been treated by soaking and cooking it in an alkali solution, usually something called limewater.
This process is called nixtamalization, and it also produces two additional characteristics of hominy that distinguish it from ordinary field corn (aka dent corn, or simply maize), which is what's used to make corn flakes, corn meal, and yes, polenta.
First, nixtamalization frees the niacin (vitamin B3) in the corn and allows it to be absorbed in our digestive tracts. And second, it produces a chemical change that allows the proteins and carbohydrates in the ground hominy to physically stick together. This means that adding water to the ground hominy flour (called masa) allows it to form a dough. Without it, it would be impossible to make corn tortillas — to say nothing of tortilla chips.
Nixtamalization also helps loosen the hulls on the kernels, making hominy easier to grind, expanding and gelatinizing the starches while also unlocking flavors and aroma. (Thus, grits are tastier than polenta. Deal with it.)
Some of the confusion in terms also comes from the fact that polenta (made from ground field corn) is sometimes called "corn grits" while grits (made from ground hominy) are alternately called hominy grits or Southern grits. So with all these different foods with the word "grits" in their names, it's easy to conflate them all into a single thing.
But remember: grits are made from hominy, which is nixtamalized corn. It has a different flavor from polenta, a different nutritional profile, and also different properties as far as being able to make it into a dough.