Re: why does decaying food suck in a balloon in a bottle rather then expand.

why does decaying food suck in a balloon?
Interesting question because ordinarily, decaying food in a closed 
container would make the balloon inflate. 
Most food decay is caused by bacteria that form gas.  
In fact, a warning sign of food going bad is the container puffing up. 
For instance, if you have a can or jar of food that puffs up, do not eat 
that food, do not taste that food.  Put the can in a plastic bag and either 
return it to the store or call your health department. 

Usually the gas is CO2 (Carbon dioxide) but depending on the bacteria, it 
could also be hydrogen, methane, and stinky gases such as Hydrogen Sulfide 
or mercaptan.  Scientists sometimes use the kind of gases produced by 
bacteria to determine which ones caused the decay. 

Another example of gas forming in decaying things is dead animals beside 
the road.  After a day or so, the begin to puff up because the decay 
bacteria inside them are making gas.  Leave the dead animals alone, because 
sometimes they died of disease, or were so ill they didn't see the car 
coming. Call the city or county to pick them up.   

I'm wondering what kind of experiment you did.
Kind of food?
temperature?
You could e-mail me at:
carl.custer@usda.gov