Thursday, August 22, 2013

CORN



Corn is categorized as; dent, flint, flour, sweet, pop or pod, based on its kernel characteristics. 
The majority of corn grown in the U.S. is YELLOW DENT which has kernels with vitreous spikey
endosperm (starch granules contained within a protein matrix) at the sides and back, and a 
central core of soft floury endosperm (mostly starch granules). As the kernel dries the floury 
central core collapses on itself producing a dent or sunken area on the top of the kernel. Average 
composition for this type of corn is 61% starch, 19.2% protein and fiber, 16% water and 3.8% oil 
(World of Corn, 2004). 
Corn production has been described as a race against time. A properly selected hybrid, planted 
on time has only a 50% (5 out of 10 years) chance of reaching maturity before frost (Farnham et 
al, 2003). For corn to achieve physiological maturity, requirements for growing degree units 
(GDUs), moisture and temperature must be fulfilled. Too few GDUs and development stops 
before maturity is reached. Too little or too much moisture at critical growth stages can be a 
serious growth deterrent and yield limiting factor. Similarly, too low or too high temperatures 
result in delayed growth and reduced yields. 
Having achieved physiological maturity the emphasis is on maintaining quality. There are two 
areas of concern; kernel moisture content and kernel integrity. In a normal season, kernel 
moistures of mature corn at harvest will range from 25-17% wet basis. At these levels the kernel 
is at risk to fungal attack, so some form of preservation must be utilized; drying, oxygen 
limitation (ensiling) or chemical preservative. Of added concern is mechanical damage to the 
kernels. Hellevang and Wilcke (1996) stated that mechanical damage to kernels is minimized 
during harvest when moisture content is about 22%, with increased damage observed above and 
below that level. Mechanical damage, either from threshing or handling, results in ruptured or 
cracked pericarp that can lead to further lost quality during forced-air drying, handling and 
storage. 
Corn in commercial channels is assigned an official grade based on a set of quality descriptors; 
minimum test-weight (weight per unit of volume