Re: why do spots form on ripe bananas? what are they?

A little banana history first....
Origins and importance of banana as a food crop
Banana is one of the most fascinating and important of all crops. It is a 
large monocotyledenous herb that originated in Southeast Asia. Virtually 
all 
of the cultivars that are grown are thought to have been selected as 
naturally occurring hybrids in this region by the earliest of farmers. In 
fact, Norman Simmonds proposed that banana was one of the first crops to 
be 
domesticated by man. In writing of the beginnings of agriculture in 
Southeast 
Asia, he concluded, "It seems a reasonable assumption that the bananas 
evolved along with the earliest settled agriculture of that area and may 
therefore be some tens of thousands of years old."

Bananas are generally ripened in storage rooms with 90 to 95% relative 
humidity at the outset, later reduced to 85% by ventilation: and at 
temperatures ranging from 58° to 75°F (14.4°-23.9°C), with 2 to 3 
exposures 
to ethylene gas at 1: 1000, or 6 hourly applications for 1 to 4 days, 
depending on the speed of ripening desired. The fruit must be kept cool at 
56° 60°F (13.3°-15.6°C) and 80 to 85% relative humidity after removal 
from 
storage and during delivery to markets to avoid rapid spoilage. Post-
ripening 
storage at 70°F (21°C) in air containing 10 to 100 ppm ethylene 
accelerates 
softening but the fruits will remain clear yellow and attractive with few 
or 
no superficial brown specks.
The larger spots on the bananas are bruises.  The smaller spots on the 
bananas are part of the ripening process, like an apple becoming wrinkled 
as 
it ripens.  Basically the gases like carbon dioxide are the reason for the 
ripening and the evolution of the brown spots.  Banana producers use 
Ethylene 
gas to start the ripening process after the banana has been cut from the 
tree 
long before it being ripe like you and I know it.

Ethylene plays a crucial role in the ripening. It is produced by bananas 
in 
natural conditions, however in much smaller quantities that are supplied 
in 
the chambers. An increased dose of ethylene accelerates the ripening 
process 
which is very important for trading.

Ripening process consists not only in changing the color of the peel, but 
also in breaking the starch into plain sugars which in turn influences the 
taste of the fruit. In green bananas starch and plain sugars are in the 
ratio 
of   20 to 1 whereas in yellow fruits the proportion is reversed and is 
1:20. 
An average process lasts 4-8 days depending on the program chosen by the 
ripener.

Thoroughly defined chart of banana ripening colors has been set. It 
determines an international banana color chart.

Bananas are the main factor determining the turnover in fruit and 
vegetable 
trade. They are usually bought spontaneously. They are graded on a 
standard 
international color chart.  Their ripeness phase influences the sold 
amounts 
and market research shows that most consumers prefer color 5 when buying 
bananas. 

Color 2 – green bananas (in ripening chambers, before gassing). 

Color 3 – bananas more green than yellow (in ripening chambers, later 
gassing).

Color 4 - bananas more yellow than green (color 4 is an ideal phase for 
retailers).

Color 5 - yellow bananas with green ends (consumers favorite color, after 
3-4 
days at home it becomes color 7), this phase should be most often 
displayed 
and sold.

Color 6 - yellow bananas (remain in their phase 2-3 days and become color 
7 ).

Color 7 - yellow bananas with spots (a good quality shop offers them at a 
reduced price, separated from color 5 ).