Page 40 - Craft of Whiskey Distilling

27 | AmErICAn DIstIllInG InstItutE
ging up the mash screen or channelizing the mash which will leave extract behind. A lauter time of 60 to 90 minutes is normal.
How do you know when to stop running off?
Contrary to what you might think, it is not “when the fermenter is full.” It is when the contents of the fermenter are at the target gravity. We are targeting an 8% ABV in our fermented wash.
The formulation above should yield a starting gravity of 1.074 SG (17.87 Plato/18.7 Brix) and if fermented properly will finish at 1.012 SG (3 Plato, 8.95 Brix). Reaching these targets will yield a wash with 8.16% ABV.
Note: Brix readings are typically taken using a refractometer due to accuracy and ease of use.
Once a solution begins fermenting the alcohol in solution changes how light is re- fracted. The Brix figures for finishing gravity above are corrected for this refractive differ- ence. The aforementioned software, ProMash, has a built in calculator to accomplish this conversion.
As the wort is running off, take frequent measurements at the fermenter to make sure that you reach the target SG.
It is important to make sure that the wort is aerated with either sterile air or pure oxygen as it is being sent to the fermenter. Yeast require oxygen to prepare for their repro- ductive phase. After that point, the environment must be kept anaerobic. NeVeR intro- duce oxygen after fermentation has started! Aeration is typically accomplished through an in-line air “stone” that is attached to the outlet of the heat exchanger. A stone can also be installed in the fermenter to achieve the same result. Simply bubling oxygen or sterile air into the fermenter without a stone will not be very effective because the bubbles must be quite small to go into solution. If you use pure oxygen to aerate, it is very important to not use too much oxygen as it is toxic to the yeast and will lead to poor fermentation results. If you use an oil less compressor equipped with an air drier and a sterile air filter, it is not possible to over aerate the wort.
Make sure to only pitch yeast after the wort is 70 - 72 deg. F (21 - 22 C). During fermen- tation yeast produce a good bit of heat which can raise the temperature of the wort up to 12 degrees F or more. If the wort is cast into the fermenter at a higher temperature than that and the yeast is added, it can seriously affect the fermentation outcome and possibly kill enough yeast that it barely ferments. For whisky, make sure to set the temperature controls no higher than 80 deg. F to maintain a proper fermentation.