Have you ever wanted to make cheesecake, flan, creme brulee or some other kind of baked custard, and wondered why the directions call for a water bath? As it turns out, water cannot exist at a liquid state above 212F (at least not without external intervention). Even better, water has a very high specific heat, meaning that it takes a lot of energy to raise its temperature. This is important, because egg proteins actually coagulate at about 165F, unless they are tempered, in which case they actually coagulate at about 185F. While water may boil at 212F (and that's a full-on rolling boil), it simmers closer to 186F. This is pretty important in the case of baked custard. If you put a custard in a 350F oven with no protection, you run the risk of cooking your proteins too quickly, which can give you a grainy texture. If you put them in a water bath, the water absorbs a lot of that energy, which allows the custard to move to that tempurature more smoothly. You still have to take them out before they actually reach that tempurature though, so that they can coast to a smooth finish.
I decided to test this myself, using a standard creme brulee mixture:
4 egg yolks
2 cups heavy cream
1/4 cup sugar
2 teaspoons vanilla extract
Yes, that's right. Any more than a single serving could kill somebody. This dessert is not for the weak of heart, literally. The procedure is simple: First, preheat the oven to 325F. Heat the cream to a simmer. While that is happening, whisk together the egg yolks and the sugar. Slowly pour the cream into the egg yolks, whisking quickly to keep the egg from scrambling. Go ahead and add the vanilla at this point, and then strain through a fine-mesh seive. Pour into four ceramic ramekins, and then put those on a sheet pan with high sides. Put this pan on the oven rack first, and then pour in enough hot water (just under a simmer) into the pan to come about 1/2 to 3/4 of the way up the sides of the ramekin. If you want an extra layer of protection, put a tea towel in the pan first, underneath the ramekins. Don't worry, the water will keep it protected, and it will help protect the bottoms of the custards from the heat below. Bake until the centers are just a little wobbly (usually 15 to 20 minutes) and then remove the ramekins to the counter. Leave the water bath in the oven and let it cool down in there, lest you splash yourself with scalding water. When the ramekins have cooled enough to touch with your bare hands, move to the refrigerator and chill for at least an hour. Then sprinkle with a little sugar, and burn the sugar with a torch, or under the broiler. If you're French, you will actually burn the sugar. Brulee means burned, not golden brown. If you're American, you will likely wimp out and just go for golden brown. Me, I like it burned.
In my experiment, I tested four different baking vessels, each with and without a water bath. In addition to the standard ceramic ramekin, I used a Pyrex baking cup, a mini cheesecake pan (aka an empty tuna can, and yes, it was cleaned) and a silicone cupcake pan (heart-shaped, left over from Valentines day). The tuna can may not seem very standard, but I used it to represent a standard aluminum cake pan or springform pan. And yes, I do bake mini cheesecakes in tuna cans all the time. The layout of the pan was as follows:
I did not use a tea towel, but I did use hot water, on one half. The pyrex went towards the back of the oven, and the oven was at 350F. After 14 minutes, I pulled the non-water bath custards out, except for the silicone one (because it was attached to the water bath one). At 16 minutes I pulled the water bath ones. I let cool, then refrigerated them all and brought them to work with me the next day. There, I recruited 3 other coworkers for a taste-test. I did not do the burned sugar on top, because I didn't want it to get in the way of the tasting, plus it would have ruined the silicone. In each of the following photos, the custard cooked in the water bath is on the right.
As it turns out, all of the water bath custards were soupy. I just didn't leave them in there long enough. In contrast, all of the non-water bath custards were set up, but grainy. What's worse, they all seemed to have been boiling, which left bubble marks on the top. Still, there were some obvious differences between each cooking vessel.
First, the Pyrex. It may be good for casseroles, but it did not perform well with custards. Still, it was certainly not the worst. The non-water bath custard was relatively grainy, but one taster prefered the flavor of the water bath version, even though it was way too soupy. In fact, it was probably the second soupiest, but one of the best tasting.
Ceramic. There is a reason this is the traditional baking vessel for creme brulee. Ceramic is a thermal battery, so once it got up to temp, it held on, even when pulled from the oven. This was greatly beneficial in the carry-over cooking that happens. Unfortunately, even though it looked set up when it cooled, it was still soupy inside. The lesson here is that it can take a trained eye to pull a creme brulee at the proper wobbliness. 3 out of 4 tasters prefered the flavor of this one. Despite the soupiness, the water bath version did set up the best.
Alunimum. By far the worst performer. It doesn't hold onto heat, and so when it was pulled from the oven, the custard was left to fend for itself. This was definitely the soupiest. The non-water bath version was grainy, but both still tasted pretty good.
Silicone. While this may have performed better for setting up the custard, it was definitely not the right vessel for baked custard. The non-water bath custard was the grainest (as it had been in the longest, I'm sure) and one taster mentioned that it was almost like cheese. Even the water bath custard didn't taste that great, though it set up second best. While it wasn't the worse performer for physics, it was definitely the worse in taste.
So that was the creme brulee experiment. By the end of it, we were all pretty sick of creme brulee, and had a coating of fat on our tongues that we were anxious to get rid of. But I think we all learned a lesson or two from this experiment.