What makes the Pillsbury canned biscuits puff up?

It could be achieved with almost any leavening, but I suspect it's baking soda or baking powder, and not yeast.

You'd just need to package it before the reaction is completed, and let it finish in the container. This would create additional gas, which would pressurize the can.

As for why it doesn't continue to rise, it's because they can control how much leavening goes in, so they'll have a known amount of gas created. Once that gas gets to one atmospheric pressure (roughly, depending on how close to sea level you are), it'll expand appropriately.

It's effectively the same sort of process that happens with fizzy drinks -- when you open the bottle or can, you allow the interior pressure to equalize with the surrounding, which causes the bubbles to escape. The difference in that case is that the bubbles are dissolved in the liquid, and so may need some agitation or nucleation sites to escape. But there's still a fixed amount of bubbling that could happen.

I used to make the store brand version of the Pillsbury canned biscuits. It was true that the CO2 is the gas that creates the pressure. The dough is made by measuring all of the "scaled" ingredients to get the proper mixture, which in turn controls the amount of gas created. It is then pumped onto a conveyor where it is sheeted. This is similar to rolling it with a rolling pin. This is how the thickness is determined. After that it is cut with a die similar to a cookie cutter. (although for mass production and varies based on what size and shape desired...Look up rotary die cutting for biscuits-- this was not the tool we used but is the most common way that bakery manufacturing cuts sheeted dough).

We did retard the gassing by keeping the production room cool until the product got to the canning process. Then we allowed the process to warm. This allowed the cans to "gas up" This process actually helps the can seat or seal. The metal lids are just crimped (rolled with cams) onto the cardboard side. The gas actual pushes on the can structure until it latches together.

My suspicion is that the dough is pressurized, which shrinks the gas bubbles in the dough and allows Pillsbury to make smaller, denser containers of dough. When you open the can, the bubbles can expand again, making the dough puff up. I don't have any proof of this, but this Yahoo Answers page mentions it (http://answers.yahoo.com/question/index?qid=20080513195851AABE3vl) and the "Biscuit Bullet" myth (as seen on Mythbusters) seems to corroborate it also.

I suspect the leavener that does the initial puffing up is ammonium bicarbonate. Ammonium bicarbonate breaks down completely to CO2 + ammonia at temperatures above 30 some centigrade, is a common biscuit ingredient for that reason, and is featured in at least one of Pillsbury's recent dough patents.

This is likely not correct answer, as ammonium bicarb dioesn't appear on the ingredient list SAJ14SAJ provides.

My guess is that they are packaged in a vacuum which removes any air and other gasses. Upon opening, air rushes in and the dough pops out. Just like a sponge will when sealed in a vacuum.