I’ll admit it doesn’t sound all that appetizing just to say it, reader Jo. Lamination is a word most people associate with driver’s licenses, though the word actually means “alternating layers”. Puff pastry is made of 729 alternating layers of butter and dough. Some people like theirs with 2187. And while that might sound like a lot, the difference between 729 layers and 2187 is but one more “turn” — or letter folding — of the dough.
How do laminated doughs work? Well imagine if you will a cross section of a piece of puff pastry, with all its layers of butter, interspersed with amazingly thin sheets of dough. Put that in a hot oven and some very interesting things happen. First the butter melts, creating gaps between the dough sheets. Shortly afterward, as the heat rises, the starch in the dough begins to gel and toughen. As the interior temperature rises up above the boiling point the water in the dough (the dough is 50% water) and the butter (the butter is 17% water) converts to steam. That steam collects in the gaps where the butter once was (before it melted) and begins pushing outward in all directions. The sheets — which are becoming increasingly rigid — start to push apart from one another and the whole mass expands, becoming up to 7 times thicker then the original dough sheet.
I know what you’re thinking: that’s not a particularly good return on all that steam power. Doesn’t steam expand to 1400 times the volume of the water it came from? Why isn’t the finished pastry twelve feet tall? An excellent point. The reason is because the vast majority of the steam escapes out the sides as the pastry bakes. Heck, I’ll still eat it.