Fermenting the wash
Once all starch is converted to sugars, the wort is almost ready for fermenting.
Cooling the Wort
Methods to cool the hot wort:
- You could leave it overnight to cool, but then you risk letting
an infection get started.
How to use an immersion chiller: Lower the copper coils of the wort chiller directly into the brew pot. Make sure that the wort chiller is properly cleaned and sanitized and your heat source is turned off. Turn on the hose so that water continuously fills the tubing. Allow water to run through the wort chiller anywhere from 15 to 60 minutes. Higher cooling efficiency can be reached in case you stir the hot wort during the cooling.
I have a counterflow wort chiller for my beer brewing. It's a
20' piece of 1/2" ID copper tubing inserted inside a 19 1/2'
piece of 3/4" ID rubber hose. This whole thing is wound into
a coil around a beer keg (then the beer keg is removed...). The
inside of the chiller has to be spotless and sanitized to keep
from contaminating the (then cooled) wort on its way to the fermenters.
Some added luxury is that I use a fluid pump to pump the hot wash in less than 5 minutes through the heat exchanger and manages to cool it down to the pitching temperature needed. I do no longer need to use gravity to force the hot wort through the chiller.
Prepare the fermenter
Make sure that you rinse the fermenter thoroughly before using it. Residu of cleaning materials like bleach or anthing else which remain in the fermenter will most likely seriously hamper the fermentation or even kill the yeast!
Pitching the yeast
Pitch a sufficient volume of yeast(slurry) A 25L wash at 1.080 will need about 3 cups of slurry. If using dried yeast, it can be helped along by letting it soak in about 1C of warm (24 °C) water for about an hour beforehand. If the pack you're using is one of those small ones, it will pay to grow it up to a suitable size before using it (see the section regarding the yeast starter).
If using the Turbo yeasts, pay particular attention to the temperature. Turbo yeast can raise the temperature of the wash by 5-8 °C, so don't add them until the wash has cooled to about 18-20 °C.
Close the fermentor, and use an airlock.
If the fermenter doesn't bubble, check that the lid is sealing well. If you squeeze the container when you put the lid & airlock on, the water should move up in the airlock, then drop again when you let go. If it doesn't, then the lid isn't on correctly.
The optimal fermentation temperature
Temperature control is very important during fermentation. Yeast is a living organism, and will die if too stressed. Both alcohol and temperature stress it. With no alcohol around, it won't die until about 40 °C. At 14% alcohol, it will die at 33 °C, and at 25 °C if in 20% alcohol.
If you keep the temperature around 28°C - it works, but preferably keep the temperature below 25 °C.
Impact on volatiles: Lower temperatures will also result in less volitiles. When the temperature has been kept below 30 °C the production of fusel oils is minimal, and is extremely small if kept below a maximum of 25 °C.
Impact on fermentation speed: Low fermentation temperatures (15 °C) will slow down the fermentation speed with greater time for the risk of infection to set in. At normal temperatures (25 °C), it will take 3 days to ferment 0.24 kg/L sugar versus at 15 °C it will take nearly 2 weeks.
Higher fermentation temperatures will result in more fusels being formed.
Maintaining the right temperature
Easy ways to maintain the temperature in cooler climates:
My favorite set up is the last option, refrigerator which can also heat in combination with a stainless steel conical fermenter.
Easy ways to maintain the temperature in warmer climates:
Note: If you are fermenting large volumes, you may need to actually cool the wash. The larger the amount you are trying to ferment, the harder it wil become to control, yet it is critical that you try to keep it all at 25 °C plus/minus only 1 °C. You may find washes larger than 200L difficult to control & keep cool.
Secondary fermentation is the fermentation phase that takes place immediately following the primary high krausen phase. Wine and beer makers will recognize the pattern whereby their fermentations start out with a lag phase followed by a vigorous bubbling phase, often with foaming, then it settles down to just spurious bubbling. This vigorous fermentation is the high krausen phase, or primary fermentation. After that, the mash or must settles down to a spurious bubbling, this is the "secondary fermentation" and it usually takes one or two weeks for beer and one or two months for wine. After this, the beer or wine is left to age or lager.
A mash intended for distillation only needs to undergo the primary/high krausen phase.
Rotten egg smell
Sometimes you will notice a not very pleasant "rotten-egg smell ..." This is due to the formation of hydrogen sulphide, mercaptans, and dimethyl sulphide. All of these compounds are usually consumed later in the fermentation in the case of beers and wines, but with distilled mashes, any amount of contact with copper in the construction of the still will instantly remove it. Not to worry about it.
The end of the fermentation
You determine the end of fermentation with these signs:
Test the gravity of the wash with your hydrometer. The specific
gravity should drop to approx 0.980 - 0.990 g/mL and have ceased
bubbling within 5 days.
In case you have used a heat source during fermentation, switch it off, and let the finished yeast settle over a couple of days to the bottom of the container.
Rack the wash from the sediment, into a clean fermentor. Clean the first fermentor and over the period of the next 3 -4 hours continuously siphon the wash from one fermentor to the other for 3 or 4 times then let it sit for 30mins, and repeat. This degasses the wash and aids clearing.
You can also speed up the settling of the yeast by using finings (eg gelatin - 2g in 100mL to settle 25L, bentonite or some Sparkalloid) or even by placing the wash in the freezer, to chill it fast & knock the yeast down. Passing the wash through a simple filter, or even a couple of paper towels to clear out the remaining yeast will also help improve the quality you later get, but is by far the worst approach.
There are also commercial products on the market such as "turbo
clear". I do not use any specific products or technics, just
let is settle for a day after racking the wash from one fermentor
into the other.
You can use some of the remaining yeast as a basis for the next fermenation batch, however there is a certain risk for contamination. I prefer to start with a fresh yeast and just throw away the remaining old yeast from the fermenter.
Transfer the wash to the still
Take a sample of the cleared wash and measure the final SG and alcohol content. It is alwasy a good thing to make notes so in case something goes wrong along teh way, you can trace back what happened. It will also allow you to recreate the best whisky you have made at a later stage.
Siphon the clear wash into the still, and you're ready to go!