One of our major scientific and technological advances has been in the area of harnessing the activities of microorganisms. For years it has been known that numerous kinds of yeast, fungi, and bacteria have a direct relation, either favorable or unfavorable, to operations such as brewing, wine making, and cheese making. One of the most recent applications of microorganism is in the search for additional sources of protein (SCP). These have emerged from small-scale or family arts to the present industrial scale. Only in the past few decades, the advantage of exploiting microbial activity has been fully appreciated, owing to advances in biotechnology.