Availability of Oxygen-The degree of anaerobiosis is a principal factor controlling fermentations. with yeasts. when large amounts of oxygen are present, yeast cell production is promoted.

人类通过研究，作为好奇而得到的产物，已开发了一批控制自然过程的系统。其中之一就是通过控制（也包括促进）微生物的生长来保藏食物。