What is a fermentor?

Tuesday 3 March, 1998

Marcus Wischik

In general terms, a fermentor is something that, as its name would suggest, ferments; this is, however, not a simple process. The process of fermentation has been known of for thousands of years, but has been mainly used over this time to the glucose found in various fruits, seeds and tubers into alcohol, later used for human consumption. In recent times, however, with increased knowledge of bacteria and fungi, fermentors have been put to a more (some would say) productive use.

The general idea behind the fermentor is to provide a stable and optimal environment for bacteria, in which they can reproduce and do whatever they do. In terms of bacteria used to ferment grapes and grape juice into wine, they would 'eat' the sugar-rich juice of the grapes, and then excrete both carbon dioxide and alcohol. The grape-mush (having been trampled into a sludge by willing volunteers) is left in huge vats that are kept at a more or less constant temperature. This allows the bacteria found naturally in the atmosphere, as well as a number of fungi (notably botrytus, the so-called 'noble rot', which is highly favored by wine-growers, as it will convert more sugar into alcohol than solely bacterial action would allow. It is, however, a bad example, as botrytus would usually infect grapes still on the vine) to establish colonies within the nutrient-rich sludge. As the ambient temperature within the vat is close to, if not exactly, the optimal temperature for bacterial growth, the bacterial populations within the grape-mush increase. As the population of bacteria in the mush increase, the rate of sugar-alcohol conversion is increased. For wines with an especially high alcohol content, additional amounts of sugar can be added to the sludge to give a greater amount of alcohol to the end product. The purpose, then, of fermentors in the wine industry is to allow colonies of bacteria to develop, which can then be used to create a useful, if not valuable, product.

More scientific uses of fermentors would include the those used to grow large quantities of genetically engineered bacteria. These bacteria, having had the genes that code for various proteins (human insulin for example) spliced into them, will grow and reproduce, and will express the inserted gene. This will result in the desired protein being released into the growth medium, from where it can be harvested, purified, and then sold and / or used. The growth medium for these fermentors has to be tailored specifically to the requirements of the bacterium that is being engineered. When a suitable subject has been chosen, the pH, temperature, light, pressure and nutrient concentrations that would give that bacterium optimal growth rates are selected and prepared. The modified bacterium would then be introduced to the growth medium, and left to grow. Eventually, the contents of the fermentor would be removed, allowing for the extraction of the desired protein.

A fermentor, then, is simply put an optimal environment for bacteria and / or fungi to grow in, and the cultivation of said organisms will yield a desirable substance.

Copyright © Marcus Wischik 1998