Biotechnology, in its most general meaning, is the use of biologic processes to create a product for human use and benefit. Today, when people use the term biotechnology, we usually think they mean the application of modern methods of manipulation of DNA (deoxyribonucleic acid), the genetic information of an organism, to make a product. In fact, biotechnology is ancient, providing the basis for making a wide range of products, including bread, cheese, beer, and wine. These early forms of biotechnology relied on fermentation, the breakdown by microorganisms of organic molecules, particularly sugars, into simpler compounds, often CO2 (carbon dioxide). In practice, fermentation involves holding the material under conditions that allow the microorganisms to increase in number, and to change the original material through chemical reactions inside the cells. The starting material in fermentation can be bread dough, made of flour, water, and yeast, or grape juice plus yeast.

To make bread, after the dough is kneaded to make the gluten (flour protein) stringy, the dough is kept at a warm temperature to allow the yeast cells to multiply in number. The yeast cells need energy to grow, so they break down sugars in the flour to CO2, creating pockets of gas. This gas makes the dough rise. When the bread is baked, the gluten dries out and the bread is filled with many small holes. Wine makers grow yeast submerged in liquid grape pressings.
This deprives the yeast of oxygen so that it produces ethanol as a waste product when it metabolizes sugar. A slightly more complicated process is used to make beer, but the principle also involves growing yeast cells without oxygen so that they produce ethanol as they make energy. Cheese is also made through biotechnology. Rennin, a protein found in the stomachs of young cows, is added to milk to make cheese. (Today, rennin is usually made with modern biotechnology
methods.) The rennin breaks down casein, the major protein of milk, into small pieces. Then, cheese makers add bacteria to milk to convert (ferment) the lactose sugar in the milk to acid, which causes the casein fragments to curdle, making them form semi-solid lumps. The flavor of cheese becomes more intense as it ages, and the flavors concentrate. Adding certain molds during the aging process turns cheese blue in color.