Fermenting the wash

Once all starch is converted to sugars, the wort is almost ready for fermenting.

Cooling the Wort
Before you pitch the yeast, you need to cool the wort down below 26°C. If the temperature is above about 34 °C, it will kill the yeast. The rate and length of fermentation is adjusted by the pitching temperature, which in turn can influence the flavours.

Methods to cool the hot wort:

- You could leave it overnight to cool, but then you risk letting an infection get started.
- You can use an immersion chiller. (Relative low cooling capacity and significant volume of tap water needed.)
- Us a counterflow chiller.

Immersion chiller Counterflow chiller

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.
I personally prefer to use a stainless steel heat exchanger from a central heating system which is also working as a counterflow cooler. The benefit of it is that is uses less space and is easier to handle and can easily be found on the internet at fairly limited cost. It is also sold through homebrew stores under the brand "Therminator™ Stainless Wort Chiller" from Blichmann Engineering, but at a failry high price.

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:
- keep the fermenter in a small cupboard or box with a light wattage lightbulb combined with a thermostatic switch to supply heat (but shield the bulb so that the beer doesn't become light-struck). You can even add a fan to circulate the heated air in the cupboard.
- Use an immersion heaters (like those for tropical aquariums) - but these can be tricky to sterilise, you need to get the wires through the lid in an airtight manner, and if you lift them out of the brew without turning the power off, they can quickly overheat and burn-out.
- Put the fermenter into a larger drum/container, fill the gap with warm water and then use an immersion heater to keep the outer water warm.
- Put the fermenter in a small refrigerator which can still cool, but also is equiped with the light bulb/fan to increase the temperature in winter.

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:
- Put the fermenter in a refrigerator.
- Dropping in frozen 2L softdrink bottles of water (make sure they are sterile!)
- Have running cooling water pipes through the fermentor.

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

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:
1. There is no more bubbles coming to the surface.
2. There is no more hissing noise inside the vessel.
3. Gravity of the mash sinks equal or below 1.00
4. The mash does not tast sweet anymore.
5. It has been sitting in the fermenter for three weeks.

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.
Once the fermenting is over, it is important to arrive at a very clear wash without a yeast cloud. During distillation, yeast will give a specific flavor which you like to avoid, especially in case you are aiming for neutral clean alcohol.



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!



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