I've been brewing an ale last week and next step is to cold-crash. I tried collecting some CO2 in a keg (mostly to flush the keg of O2) and rubber glove to compensate for the suck-back when cold-crashing. But it got me worried it might create such a vacuüm, it actually can bend/pop-in my band-new stainless fermentor. How much, volume wise, does CO2 (and beer I guess) shrink, when going from fermenting temp to near freezing? What is the formula to calculate this?

The setup:

The numbers:

Total volume of fermentor: 35L

Beer volume: 19L

CO2 volume in fermentor: 16L

CO2 volume in keg: 10L

CO2 volume in glove: about 1L

The glove was connected at the end of fermentation, the tube was dipped in starsan before. It was a bit too late, it only swollen a bit, my guess is about a liter.

To make it a bit more complex, only the fermentor is in the fridge, so from the total volume of 27 liters of CO2, only 16L will go from 20C to 2C. The remaining 11L (outside the fridge) stays at 20C. So the pressure reduction is spread out over the total volume.

Many thanks.