Why use yeast to produce ethanol from cellulosic biomass?
This question has been answered clearly since the early 1970s by the collective voices of scientists all over the world. As described elsewhere in this website, experts concluded that ethanol could be a renewable fuel to augment or replace gasoline as a liquid transportation fuel. For centuries, the Saccharomyces yeast have been used to produce beer and wine by fermenting grains and other starch rich agricultural products such as rice, wheat, and potatoes. Furthermore, yeasts are the only microorganisms used for the production of ethanol in industrial plants. These industrial production plants have always used glucose-based feedstocks (corn and other starch rich agricultural products) as well as glucose and fructose rich agricultural products such as cane sugar.
On the other hand, cellulosic biomass consists of materials often considered to be waste products – including corn stover, straw, wood, grasses, and others. These materials represent the world’s richest – yet untapped – renewable resources. However, it was known that most types of cellulosic biomass contained two major fermentable sugars – glucose and xylose.
In the 1970s, scientists worldwide began to test the Saccharomyces yeast’s ability to ferment xylose. What they found was that the naturally occurring Saccharomyces yeasts were not able to ferment xylose. As such, worldwide efforts were devoted to finding new yeast that could ferment xylose to ethanol. However, these efforts were not successful.
In the early 1980, the global scientific community realized that it might not be possible to isolate naturally occurring yeast to effectively ferment xylose to ethanol. Thus, scientists worldwide began to genetically engineer the Saccharomyces yeast to ferment ethanol.
The most important reason for using yeast to produce ethanol is that yeast produces ethanol very efficiently under acidic, low pH conditions. Under these conditions, no toxic microbes can survive, propagate, and contaminate the production. For more than a thousand years, humans have employed yeast to produce wine or ethanol using a range of methods - from primitive techniques to very sophisticated industrial technology. So far, no hazardous incidents have ever been reported.
The following are some of the additional reasons why yeast should be used for fermenting sugars from cellulosic biomass to ethanol:
It has always been the microorganism traditionally used for industrial
● Proven robustness in industrial fermentation processes.
● Well accepted by industry.
● Co-products can be used as animal feed or for other applications.