Re: How do the gases from rotting foods in a enclosed area expand a balloon...

Answer:
Like many seemingly simple questions, there is more to this one than you
want to know. You have chosen a variety of plant products -- some fruits,
some vegetables.  In general, their main ingredient is water; but the
special ingredients of plants are pectin and cellulose, with other
carbohydrates and protein.  

Bacteria and molds will attack these plant products.  These microbes
produce substances called enzymes that attack the pectin, cellulose,
carbohydrates and proteins.  Many fruits and vegetables have a waxy outer
layer that makes it very difficult for bacteria and molds to get in. 
However there are almost always small bruises and cuts in this outer layer
that allow bacteria and molds to enter.  Bacteria usually grow faster, but
molds are more tolerant of the acid in lemons and tomatoes.  Either way,
the enzymes digest the constituents of the produce so they can be used to
make more bacteria or molds.  

The carbohydrates in plants, including pectin and cellulose, are made of
carbon, hydrogen, and oxygen.  Proteins contain these elements, as well as
nitrogen.  The carbohydrates and proteins serve as building blocks for the
new bacterial and mold cells, but they also serve as energy sources. 
Energy production yields the usual products of combustion, carbon dioxide
and water (an oxide of hydrogen).  Nitrogen from protein may also be
oxidized.  However, in a closed container, available oxygen may be used up.
 After that, the bacteria or molds must rely on less efficient systems to
produce energy.  Carbon and hydrogen may combine to produce methane, and
nitrogen and hydrogen may combine to produce ammonia.  Of course, there are
many other breakdown products in rotting fruits and vegetables that we
detect as undesirable odors.  

The main point is that, in the course of energy production, solid
substances from the fruits and vegetables get converted to gases.  Carbon
dioxide and methane are naturally gases, and some of the water occurs in
its vapor state.  A given quantity of matter occupies more space when it is
a gas because the molecules are in faster motion than when it is a solid or
liquid.  Therefore, the gases generated from converting carbohydrates and
proteins into energy for the growth of bacteria and molds expand and
inflate your balloon.  Of course, if the rotting fruits and vegetables are
just in the refrigerator, they won’t pop the refrigerator door open, but we
will smell the gases when we open the refrigerator.  A more scientific
explanation of how bacterial and mold enzymes attack fruits and vegetables
is in the reference that follows.

Dean O. Cliver

Montville, T. J., and K. R. Matthews.  2005.  Food Microbiology, an
Introduction.  ASM Press, Washington, D.C.  Spoilage of produce and grains,
pp. 258-265.