Since I re-shared my tangzhong choreg earlier this week, I thought it would be useful to go into the tangzhong method in a little more detail. As I said, I’m a huge fan of it, and use it all the time, at least when appropriate for the bread in question.
As I mentioned in that post, the tangzhong method involves heating a portion of the flour and water in a bread formula until the starches in the flour gel, turning the mixture into a pudding-like paste. The paste is then added to the final dough, along with more flour and water. The method seems to have been invented in Japan—where it is known as “yu dane”—in the middle of the 20th century (where it was use to improve the texture of Hokkaido milk bread), but it was popularized in the 1990s by Chinese writer Yvonne Chen in her book The 65° Bread Doctor (65˚C = 149˚F, which is just above the temperature where starch and water form a gel). Which is why the Chinese name has stuck, even though it originated in Japan.
There are two related reasons to use a tangzhong in a bread: a soft texture and increased resistance to staling. Because the water in the paste is bound up within its starches, it allows a baker to add more water to a dough without making the dough stickier or softer. (I think of it as “stealth” hydration.) In other words, you can make a dough with the same easy-to-handle consistency as another that lacks a tangzhong, but with considerably more water in it. On average, tangzhong breads contain an additional 5 to 10% water.
More water means a softer bread, because water has a tenderizing effect on gluten. That’s why a tangzhong is so useful in breads like choreg, brioche, pain de mie, and challah, all of which are meant to be soft and plush-textured.
More water also means a bread that stays softer longer as well, because the bread is more resistant to staling. Staling—also known as retrogradation—is the reversal of gelation, where the water that is in the starches gets pulled out, causing the starches to crystallize and harden. The more water in a bread overall, the slower the starches tend to retrograde.
Stale bread is not “dried out,” at least not initially, even though it can seem that way. An easy proof of this fact is toast. Toasting bread temporarily reverses the staling process—I suppose it could be called deretrogradation or progradation—by pushing the water that still surrounds the starches back into them, tenderizing them again. But because by that point some of the original water in the bread has evaporated, the effect is ephemeral.
This anti-staling effect is the reason that tangzhong is so useful in choreg and other sweet breads like it (choreg contains at least 20% sugar, mine has 24%). Sugar is hygroscopic, meaning it has a strong affinity for water; this makes high sugar doughs especially quick to stale, since the sugar competes for the water in the starches. Adding a tangzhong helps to counteract this effect.
At this point you might be wondering: If a tangzhong is so great, why put only 5 to 10% of the loaf’s flour into it? Why not put all of it into the tangzhong?
The answer is simple: cooking flour and water not only gels the starches, it also denatures (destroys) the proteins that combine to form gluten. If you gel all the flour in a bread, it won’t have any gluten left to give it structure. Ten percent is about the most you can gel while keeping the crumb structure more or less intact. (This is also why it’s not uncommon to call for higher-protein bread flour in a tangzhong-style bread—as I do in my choreg—to compensate for the gluten that is lost in the making of the paste.)
Another reasonable question is: Why don’t people tend to use tangzhong in lean breads like baguettes or sourdough?
The main reason is that while those breads can be tender, they shouldn’t really be soft. The tenderizing effect of tangzhong runs counter to the chewy crumb and crisp crust you generally want in most lean breads. A tangzhong also compromises gluten structure, so it’s hard to get an open, airy crumb with one in the mix.
That said, there is at least one type of lean, European-style bread that uses a cooked-starch technique that works similarly to tangzhong: porridge bread. In this case the starch in question is bound up in a mostly whole-grain matrix—like oatmeal or another cooked-grain porridge—rather than a ground, refined one. The larger particle size of a porridge means that the starch paste doesn’t combine as fully with the flour, so the bread can still have decent gluten structure and a more open crumb. And it changes the texture of the bread in a different way too: Porridge breads—relative to lean breads without the inclusion of a porridge—have a dense, moist crumb and a somewhat-less-crisp but not necessarily soft crust.
On the other hand, porridge breads are—just like tangzhong—much slower to stale, thanks to all the extra water they contain. But these breads—another favorite of mine—are a subject for another day.