On the Many Uses of Gelatinized Starch

Reader Eric writes:

Following on your melon pan recipe, I was wondering if during your research you came across any recipes that called for a tangzhong or a water roux. It’s touted as an anti-staling method, or a softness improver.

Wondering if you’ve tried it yourself. My personal experience with East Asian pastries and breads is that they are generally soft and don’t go stale quickly, which might be because of the preservatives and conditioners that are added.

Very interesting that this question should come up just now, since it’s related to the heritage/cooked flour frosting post from earlier in the week. To answer your question, Eric, I have indeed heard of the technique, but haven’t tried it.

For those who haven’t heard of the method before, it simply consists of making a “starter” or “roux” out of hot water or milk and flour — exactly like the mixture one uses to make a cooked flour frosting.

It’s odd by conventional Western standards, but I can see where it would create a bread that is at once fluffier than standard American white bread and more resistant to staling. Why is that? It all has to do with they way starch behaves when it’s moistened and heated. As discussed below, it dissolves. Which is to say the individual starch molecules begin to break off the flour granules and disperse into the water (gelatinize).

But how would that make a softer, fluffier bread? In a conventional bread dough, flour doesn’t have a whole lot of time or space to gelatinize. It does to some degree: the granules swell and lose some of their integrity. But compared to a tangzhong or “water roux” a normal bread dough is a pretty low-moisture environment, and it doesn’t stay hot for terribly long. The end result is a structure made up of larger masses of starches. I think of it like a building made of bricks: a fairly dense bread.

Add pre-gelatinized starch to the dough, however, and the result is a more random configuration of starches. The structure is airer and lighter, like a building made of I-beams: a fairly fluffy bread.

Now then, consider staling. It isn’t merely a loss of moisture, as many people think. Rather it’s a hardening that occurs as flour granules that were once semi-dissolved start to draw themselves back together. If a bread is composed mostly of masses of starches, it’s easy to see how this “re-bunching” can happen. However if the bread structure has a higher proportion of random starches in the mix, they’ll have a harder time gathering themselves together in rigid clumps. Thus the bread stays softer longer.

At least that’s my take on how it works. Real food scientists: check me on this if I’m wrong, please.