A. Some foods require moisture in the oven, as well as a milder heat source than the direct heat of the oven, such as custards, puddings, and cheesecakes.
Although you don't absolutely have to use a water bath, cheesecakes tend to crack without the moist heat and custards can become rubbery if they're not baked in a water bath.
So, what's a water bath? It's just a pan of water placed into an oven. The hot water provides a constant, steady heat source and ensures even, slow cooking for recipes that call for a water bath.
The best type of pan to use for a water bath is a roasting pan or other pan with sides at least 1-1/2 to 2 inches high. That will allow you to put enough water into the pan so it won't all evaporate before your pudding or cheesecake has baked.
You can place a pan of water into the oven, then put in your pan or ramekins, but you run the risk of having the water overflow or spilling when you pull the oven rack out.
A better way to prepare a water bath is to put your pudding or cheesecake into the roasting pan, place the pan into the oven, and add enough hot water to reach halfway up the pan.
After your food item has baked, some of the water will have evaporated, but some will remain, so be careful not to tip the roasting pan when you take it out of the oven.
If you use a spring form pan for a recipe that calls for a water bath, wrap the pan first with aluminum foil to prevent water from leaking through the bottom. Use two or three sheets in a crisscross pattern for best results.Learn more water baths in the following articles: