Re: Why Do Ripe Fruits Smell Bad?

You have posed a difficult question.  When you ask, "Why do peaches smell 
bad when ripe?", it is rather like saying why did Michelangelo make such 
ugly sculptures?  The fact is that most people like ripe fruits (and 
Michelangelo's sculptures), particularly those of the rose family 
(apples, peaches, pears, strawberries, apircots, cherries, etc.).  Your 
judgement that they stenk (sic) is quite subjective.  The proof of this 
is the large number of fruit mimics that we manufacture that use these 
odors combined with lots of sugar (fruity drinks, candy).  

Fleshy fruits ripen to display fruity colors (non-green) and fruity 
smells as attractants for seed dispersers.  A wide variety of volatile 
chemicals compose fruit odors, esters, aldehydes, and terpenes to name 
three major general categories.  A basic apple might have as many as 20 
different chemicals composing its odor, so odor chemistry is very 
complex. Prior to ripening, a process that involves the gas ethylene, 
fruits have little odor, little sweetness, and very firm flesh.

Many fruit eating animals, including humans, have instinctual likes for 
fruity flavors and smells, and generally (but not always) ripe fruits are 
safe (or safer, i.e., less toxic) and nutritious foods.  But not all 
fruit-liking animals can eat all ripe fruits, so don't eat unfamiliar 
fruits just becuase they look and smell good.  

Part of likes and dislikes are instinctual, hard-wired, built in, part of 
your genetic heritage.  However, different likes and dislikes can be 
learned, and I assume you have learned to like tart fruits.  An example 
of learned likes and dislikes is the SE Asian durian fruit, which while 
dearly loved by all my Thai friends, it smells bad to many Westerners. So 
no problem, you can have all the unripe peaches, I'll wait for mine to 
ripen.