Bag Balloons AFTER 24 hours @ 131F has passed.

That certainly seems interesting. As you may know ballooning bags is usually the result of vapor pressure at higher temperature cooking, and this doesn't seem to be your case.

Bacteria _do_ produce CO2, so in theory some bacterial breakout could produce gas, but it is my understanding that it also _needs_ O2 in order to do this, so even if there were a bag compromise, I don't see a reason there'd be a net gain of gas in the bag.

I'd probably toss it, but if there is a big bacterial problem, I'd also bet a smell test would probably root it out (if it is producing that much gas).

Maybe someone more enlightened will know the real answer.

I had this happen to me once with pork. I ended up tossing the ballooned bag due to assumed contamination but ate the finished product from the other bags once they finished cooking. Sorry I don't have more ideas as to what happened.

How were the bags sealed? Water displacement method, vacuum seal, chamber seal?

Vacuum sealer, triple sealed. It's just strange how it ballooned after more than 24 hours in the bath. The other bags are fine.

If you do mean 'balloon' as fully blown up then I would certainly throw that bag away, its likely that it is waste gas produced by bacteria. There is always some oxygen left in the vacuum bag, vacuum sealers aren't perfect, particularly edge sealers. Also not all bacteria need oxygen to thrive.

It has happened to me once with a 100hr ox tail cook at about 55C and was definitely caused by the bag partially floating to be surface, and I assume that that part of the meat was below 55C and in the bacterial incubation temperature range. Other bags that hadn't come free and floated to the surface still looked ok but I decided to jettison the lot.

I think the problem is generally more of an issue at lowere cooking temps and longer cooking times.

Its very important to make sure that the bag is fully submersed for the whole of the cooking period.

If you do mean 'balloon' as fully blown up then I would certainly throw that bag away, its likely that it is waste gas produced by bacteria. There is always some oxygen left in the vacuum bag, vacuum sealers aren't perfect, particularly edge sealers. Also not all bacteria need oxygen to thrive.

It has happened to me once with a 100hr ox tail cook at about 55C and was definitely caused by the bag partially floating to be surface, and I assume that that part of the meat was below 55C and in the bacterial incubation temperature range. Other bags that hadn't come free and floated to the surface still looked ok but I decided to jettison the lot.

I think the problem is generally more of an issue at lowere cooking temps and longer cooking times.

Its very important to make sure that the bag is fully submersed for the whole of the cooking period.

That one bag was about 1/4 full of gas. I opened the bag to take a whiff and then fed it to the disposal. There was an odd smell, nothing I've encountered before, but not what the bag should have smelled like. The bag was submerged before I left but floating when I returned. Just plain odd.

http://www.chefsteps.com/

You might try posting your question to this forum. It is a relatively new forum but it was started by three people who were involved in Modernist Cuisine so they may be another resource. From what I can tell, they themselves are very involved in answering questions posted to their site.

The bacteria that create orders, food smells bad, are produced by aerobic strains. Hence in a air free vacuumed sealed bag, these bacteria could not vegetate Remember also that some of the worst pathogens, those that produce heat resistant spores cannot vegetate under 36°F. so make use you store vacuumed packed proteins under 36°F. You cannot use the “smell test” to check for spoilage od SV foods. The saying goes, “If in doubt…throw it out.”