Fermentors closed

False. The behaviour of stirred bioreactors does not resemble closely pressure-cycle fermentors at any scale. 

When all the ingredients are dissolved the volume is brought to 40 gallons (150 liters) with tap water and the pH adjusted to 7.2 with about 60 ml of 5 N potassium hydroxide. The fermentor is then closed and the contents sterilized by being brought to a temperature of 120°C and maintained at that... 

Because the yeasts used begin to suffer thermal death at temperatures close to 100° F (37.78° C), a maximum fermentor temperature of between 80° and 90° F (26.67° and 32.22° C) is accepted generally. As the fermentation proceeds from an initial 23-24 percent soluble solids, down to approximately 18 percent soluble solids, the temperature rises quite rapidly. The lesser density of the pomace, coupled with the floatation effect caused by the generation of C02 by the fermentation, causes the pomace to float above the juice. This is known as the cap. ... 

Figure 5.7 Closed-loop simulation (case 1) concentration (key component, biomass, substrate, product in fermentor, and membrane sides) and input profiles.

With regard to the fermenters, the most common configurations are membrane recycle fermentor (MRF) and hollow fibre fermentor (HFF). In the MRF the membrane module forms a semi-closed loop with a conventional fermentation vessel the MRF gives much better performance than the HFF, where the microbial cells are loaded onto the shell-side and the feed is pumped through the lumen side. Further advantages of this system are a cell/particulate-free product stream and the reduction of capital costs. Furthermore, in these systems cell growth is a caitical point. 

The sole operational point available for an industrial plant, is located close to the results observed for the other fermentors (fig. 6). 

In a later step, fermentation converts the sugars to ethanol and CO2 in a closed vessel that is vented to the atmosphere through a one-way valve thus some CO2 is allowed to escape and pressure is maintained at 1 atm (so the fermentor does not explode ). The fermentation product, now a beer, will have a lower pH than that of the mash from which if is made a pH of 4.5 would be t)2pical. 

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