The fermentation and conditioning process takes several days to several weeks depending on the beer, indeed high gravity speciality beers can take several months to condition to optimal flavor profile. The standard fermentation unitank is a highly engineered pressure rated vessel which requires a polished finish to minimise contamination risk, which makes these vessels quite expensive. The biochemical and chemical processes occurring in the mash and boil steps are rapid but the biological process’ occurring during fermentation and conditioning are much slower. One of the major differences between large commercial breweries and microbreweries is that the latter dedicate much more time to the fermentation and conditioning process’. While the cell metabolism and biochemical process’ are not completely understood it is an undeniable fact that a superior beer is produced by yeasts which are not stressed in terms of high fermentation temperature. Fermentation executed at higher temperature results in a much faster fermentation but the resulting beer is typically much harsher and nowhere near as good as low temperature fermentation performed with the same yeast. This “slow beer” process has analogies with the slow coking process which produce amazing culinary effects. The drawback of a slower, low temperature fermentation is that the expensive fermentation/conditioning vessels are occupied for a longer time, the beer production bottleneck becomes even tighter.
In addition to being the bottleneck in the beer production process it is also important to note that the capital outlay on fermenters is very high due to the high specification finish and sanitary design requirements of the “direct contact” fermenters.