How starch and cellulose are treated to allow them to be used by yeast?

Answer 1

Starches. All potable alcohol and most fermentation industrial alcohol is currently made principally from grains. Fermentation of starch from grain is somewhat more complex than fermentation of sugars because starch must first be converted to sugar and then to ethanol. Starch is converted enzymatically to glucose either by diastase presents in sprouting grain or by fungal amylase. The resulting dextrose is fermented to ethanol with the aid of yeast producing CO2 as co-product. A second co-product of unfermented starch, fiber, protein and ash known as distillers grain (a high protein cattle feed) is also produced.

Cellulosic Materials. Each step in the process of the conversion of cellulose to ethanol proceeded with 100% yield; almost two-thirds of the mass would disappear during the sequence, most of it as carbon dioxide in the fermentation of glucose to ethanol. This amount of carbon dioxide leads to a disposal problem rather than to a raw material credit. Another problem is that the aqueous acid used to hydrolyze the cellulose in wood to glucose and other simple sugars destroys much of the sugars in the process.

One way of making cellulose wastes more susceptible to hydrolysis is by subjecting them to a short burst of high energy electron beam radiation. An alternative to acid hydrolysis is the use of enzymes. Although they avoid the corrosion problems and loss of fuel product associated with acid hydrolysis, enzymes have their own drawbacks. Enzymatic hydrolysis slows as the glucose product accumulates in a reaction vessel. This end-product inhibition eventually halts the hydrolysis unless some way is found to draw off the glucose as it is formed.

Last Updated: 06/06/2012

Answer 2

Starch is broken down into fermentable sugars through the enzymatic action of amylase. Cellulose can be hydrolyzed into fermentable sugars through the use of cellulase enzymes. Once broken down into simpler sugars, yeast can metabolize them to produce ethanol during fermentation.