Pita is made from one layer of dough, not as some think 2 layers that are joined at the edges.
So how does if puff?
The dough is often given a final proof that is drier than for risen breads. When the bread hits the hot oven the slightly dry skin seals. Really thin flat breads like pita can be baked at extreme temperatures. My lab in Sydney when I worked there used a pottery kiln for our routine test-baking of pita, and we baked them for 30 seconds at 550 degrees CELCIUS (about 1020 degrees F). Not unlike the conditions in a tandoori oven.
The sealed skin first constrains the existing gases in the small amount of dough that will turn to crumb. These expand and exert more pressure in line with the gas laws. There MAY be a VERY brief moment of additional carbon dioxide production from yeast but this will be really limited in the thinner types. But the greatest gas production and pressure comes from the water in the dough that turns to steam, lots of gas an pressure now. If you see the video in my last post you’ll see the outcome. The interior splits at the weakest point creating the taste sensation of fresh, high temperature baked pita bread. Good enough to eat on its own.
You can access a schematic of this on the google books preview of Jalal Qarooni’s Flatbread Technology book (page 71).
And why does my poolish lose weight ?
I commonly bake using a yeast poolish, a mixture of equal weights of flour and water, and a vanishingly small amount of instant yeast that is allowed to ferment overnight or longer. This long pre-ferment creates bread of outstanding flavor.
Anyway, I am, as many bakers are, in the habit of scaling out the exact amount of poolish I will need for a dough (I always bake using formulations that list ingredients by weight).In the morning i use the poolish assuming the same weight. Duh !! Some chemist I am.
Out of error the other day I had more poolish than I needed. When I weighed what I had I had 952 g. The evening before we had scaled out 500 g flour, 500 g water, and 1.5 g yeast (1001.5 g). It is clear that we’d lost in the order of 5% of the poolish weight. As I had covered the poolish I assumed this was not water loss, but loss of carbon dioxide (and maybe volatilized ethanol). Poolishes rise but at 100% hydration they are pretty weak and sloppy and gas loss would be expected.
If this was the case the weight loss would come from the conversion of starch to maltose , and the conversion of the maltose, via the fermentation pathway to CO2 and ethanol with the subsequent loss of volatiles. Anyway the result is a poolish that is more than 100% hydration (1.11 %) as the substrate comes mostly from the dry solids part of the poolish (although maltose requires the addition of 1 water molecule when hydrolysed to 2 glucose). This probably isn’t enough difference to cause dough handling problems and I can just go back to my weigh out the poolish the night before assumptions and not worry about it (until I do any poolish research, with the aim of eating the experimental outcomes of course.)