Re: How much glucose will be enzymatically converted from 1g starch?

Ethanol fermentations of starchy materials is a standard for the production 
of many food products such as beer, wine, and bread.  All of the these 
processes start with a starchy product, a seed of some kind in most cases.  
Thus, the fermentation of beer starts with barley grain.  In all cases, 
there needs to be a conversion of the starch into free sugar monomers.  For 
it is the sugar molecules, like glucose, that are used by the fungi as a 
carbon and energy source in the process of fermentation.  In this case, the 
sugar is converted first into pyruvate with the capture of chemical energy 
as ATP and the capture of reducing power (electrical energy) in the form of 
NADH through the process of glycolysis.  The NADH is used to reduce the 
pyruvate to ethanol and carbon dioxide.  This regenerates oxidized NAD that 
can then be used as a cofactor for further glycolysis.

There are a wide variety of sugar polymers known as carbohydrates.  Starch 
is a particular class that is found in plants.  It has many similarities to 
glycogen, found in animals and some bacteria.  Starch is simply a polymer of 
glucose monomers with a particular branching pattern.  There are classes of 
enzymes that can degrade the polymer to its component sugars.  Amylases that 
degrade the linear strings are commonly found, as are glucoamylases that 
degrade branch points.  These enzymes are stored within the seeds to allow 
for the conversion of starch stored in the seed into glucose for use by a 
new seedling.  In the process of beermaking, the barley grain is often 
malted.  This simply means that the barley seeds are allowed to germinate.  
This releases the amylase enzymes and enhances the conversion of starch to 
sugar.  In breadmaking, the grain is not malted, but the native enzymes are 
still active in conditioning the dough with amylases and proteases.  The 
amylase enzymes do not require added cofactors.  No ATP are needed.  No NADH 
are needed.  The conversion of starch to sugar is an exergonic reaction.  
The breaking of the carbon-carbon bonds drives the reaction and no 
additional energy is needed.  Since starch is 100% glucose, one gram of 
starch will yield about one gram of sugar.

Ethanol for use as a fuel additive is commonly made by the fermentation of 
corn by yeasts.  As I understand it, the corn is not germinated before the 
process begins.  It is simply ground and added to the yeast fermentation 
vessels.  The ethanol is captured from the vapor phase.  The plant/yeast 
biomass remaining, called spillage, is dried and sold as an animal feed 
ingredient.  The profit margin for the production is ethanol is low.  
Ethanol is a low-value bulk product.  Thus, minimal processing costs are 
desired.

Hope this helps.