Fermentors generally work with aeration rates of 0.5-2 vvm (air volume/liquid volume per minute). The methods available for sterilizing gases include filtration, gas injection (ozone), gas scrubbing, radiation (UV) and heat. Of these, only filtration and heat are practical.
APPROPRIATE CONSTRUCTION OF THE FERMENTOR
There should be a minimum number of openings in the fermentor to favor maintenance of sterility. Small openings must be made leakproof with O-rings, larger openings with flat gaskets. Whenever a movable shaft penetrates the fermentor wall, special problems of sterility maintenance should be solved.
2.7. Fermentation processes
An overall scheme of a fermentation process can be described as follows:
* Stage 1: inoculum preservation
* Stage 2: inoculum build-up
* Stage 3: fermentor culture
STAGE 1: INOCULUM PRESERVATION
The objective of preservation is to maintain strains as long as possible without cell division. The optimal method of preservation must be worked out for each strain. The following three techniques are most commonly used:
* Storage at low temperatures (2-6 degrees Celcius)
* Frozen storage (-18, -80 or -196 degrees Celcius)
Storage at 2-6 degrees Celcius is the least secure, there is a relatively high risk of
contamination and reverse mutation through frequent transfer. The frozen storage is the
most common and frozen cultures may be kept for several years. The proportion of