Although there are alternative solutions, actually the main source of raw materials for yeast is a by-product of the sugar industry, molasses. 

This product contains, as far as dry materials are concerned, 60% of fermentable sugar and 40% of non-sugar products, most of it cannot be used by yeast.

These non-sugar products, which cannot be used by yeast, would represent a noticeable pollution if they were rejected into the natural environment.

The environmental issue has always concerned yeast producers.
Several means present themselves to protect the environment :

These de-pollution treatments represent an important part of the exploitation costs and investments necessary for operating a modern yeast factory.

Through using by-products of food processing in its initial stage (sugar industry, starch industry, etc), the yeast industry strongly contributes by its commitment to environmental protection.