Food Science: Why Eggs "Rise" in the Oven

We were trying out a new bread pudding recipe this weekend, and had a shock when halfway through cooking, the custard base puffed up around the bread parts - almost like a soufflé! We hadn't been expecting that and were curious why it happened...

Actually, we're pretty sure that the same principle that makes a soufflé rise was happening in our bread pudding. In a soufflé, whipped egg whites are folded into a egg yolk base. The air bubbles in the egg whites expand in the heat of the oven, causing the whole network of egg proteins to lift ("rise") the dish.

When making a cream and egg custard like flan or crème bruleé, the goal is usually to minimize the air bubbles for a creamier and more uniform texture. Also, the eggs are normally so diluted by the cream that the protein network that forms is much more delicate. Even if there are air pockets, they are unable to lift the fragile network.

We think two things were going on in our bread pudding. For one, we whipped together the cream and eggs for several minutes to get the uniform consistency specified in the recipe. Although the recipe didn't talk about incorporating air, that's most certainly what we were doing.

Secondly, there was a higher proportion of eggs to cream in this recipe than is normal for custards - it was roughly one part egg to two parts cream (the ratio is normally more like 1:4).

This meant that the protein structure, while still relatively weak, was stronger than normal. This probably helped to retain the air bubbles in the mix even after the dish stood for several hours before baking and also helped it puff up in the oven.

That's our theory! What do you think?

(Image: Flickr member GeekStinkBreath licensed under Creative Commons)

Comments (2)

This is interesting. I recently made some "cheese puffs" that had a lot of eggs and they really turned out to be more like quichey pancakes and I couldn't figure out what happened. They didn't really rise maybe I didn't incorporate enough air. I thought the batter was too liquidy too maybe that happened for the same reason.

cass, if you were making gougeres or something with pate a choux dough, the key to those is to make sure the flour gets cooked at a high enough temp. with the water and butter - the liquid should be boiling before you put the flour in, and after it's incoporated, put it back on the heat and mix until the dough is sticky and pulls away from the sides of the pot. then add the eggs. it should be a pretty thick dough that you can actually spoon or pipe before baking. what makes this dough rise is not air in the batter but steam. another thing to remember is to not open the oven door at all for at least the first 15-20 minutes, since you'll let out the steam that's doing the rising.

i don't know if this is actually what your recipe was for, but i just had this happen to me and what you describe sounds similar, so thought i'd share.