A good question came in last night from a reader by the name of Benny (all the way from Israel by the looks of it) asking:
What causes the creation of “tunnels” in a yeast raised laminated dough? (volume is o.k.)
Large holes (or “tunneling”) is a problem common to yeasted breads (especially tight-crumbed breads like sandwich bread) as well as to muffins. The problem is usually caused by insufficient kneading in the loaf-shaping phase the first case, and over-mixing in the second. Laminated pastries don’t have “tunnels” in quite the same way, but most of us have had the experience of biting into a croissant that was basically hollow in the inside, which is the problem that Benny is most likely referring to.
What causes it? Well, fat (while it’s lighter than water) is actually pretty heavy stuff, and constitutes a significant drag on leavening. Given that croissants contain quite a bit of fat, and rely on very thin, delicate layers of pastry to lift it, it’s not terribly surprising that every so often those layers collapse under the sheer weight of it as the bake. This is especially prone to happen when layers are uneven, or there are large pockets of butter in the dough. Thus the more evenly the butter is distributed during the rolling phase, the less likely these types of cave-ins are to occur.
However there are other reasons for hollow croissants. Under-mixing the détrempe can cause the problem, since the strength of the layers is at least to some extent dependent on gluten formation. So, a little more mixing or possibly a slightly higher gluten flour might help. But then it’s also possible that the dough might simply be too darn rich. The recipe I linked to yesterday has about as much butter as a croissant recipe can stand. They’re very rich. Far richer in fact than even a specialty bake shop can afford to sell (at least at any reasonable price). That’s why when you buy a croissant they tend to be more bready than flaky, and why homemade croissants kick the can of anything you can buy, since most of us can afford to splurge on top-quality butter for the one or two times a year we might decide to make them.
Still, home bakers can move closer to a more conventional, breadier croissant by simply scaling back the size of their butter block. That will keep the cholesterol counts down while at the same time giving you a less hole-prone product.
Should none of that help, try sprinkling a tablespoon or two of flour onto your butter block before rolling (which will help the layers release from one another a bit better). Or start with a drier détrempe, since too much moisture, as I’ve pointed out in other posts, can cause the layers to stick together and fall.