Fermentation tank Size & shape (Tank Hydraulics)

Jack writes ...
    Traditionally, shallow, open, "wading pool" shaped fermenters were the most common found in old breweries/distilleries. Due to space concerns, "unitanks" (sealed on top, with a conical bottom and a valve to separate trub and yeast) have taken over, as they provide a more sheltered enviroment that, being tall rather than wide, allows companies to expand production at a fraction of usual expansion costs. After testing various fermenter shapes, it was found that the effective height (that which is actually filled) of the fermenter should be less than the fermenter's diameter. A few industrial studies show why this is so. In 1978 it was found that carbon dioxide gradients were present- the largest values being at the bottom of the fermenter. This caused s heterogeneous flow field that included isolated vortices. The maximum vortex formation was found at the top of the fermenter, which influenced temperature, sugar concentration, and Ph- effectively, tall fermenters have not one, but several fermentations taking place in parallel.

    In order to counter this effect, the best method is to use a stirring device within the fermenter, or to recirculate a small amount of the mash (maybe 5 to 7% of the total volume).

    Why was this done? Because short/wide fermenters work markedly better than tall ones. Check the numbers:

      Tall fermenter Short/wide fermenter
    Fermentation time: 10 days 8 days
    Final gravity: 1.010 1.011
    Diacetyl (mg/L) 0.350 0.060
    Clearing poor excellent
    pH at end point 4.6 4.4


    The lower pH will provede a greater stability in the mash/beer during storage/secondary fermentation/ clarifying procedures. Blind tastings have also shown that the short fermenter in an "open fermenter" form (a large stainless steel stockpot with the lid on instead of an airlock) made for a cleaner, better tasting beer/mash. For large industrial concerns, closed unitank fermenters are a good business idea. For home brewers/distillers using a large (7 gallon) stainless steel stockpot with a lid gives you a great fermenter (even compared to carboys- just watch the sanitation in the surrounding area), that will give a faster ferment and a faster clearing time. That alone reccomends it for distiller-only hobbyists, but the flavor improvementsalso make it worthwhile. Remember, a still will not make a bad mash taste good- it will only make it taste stronger. As a result of this info, I now brew my beer (and bourbon) in an open fermenter. And I'm drinking/distilling it 2 days faster as a result.


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