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Fermentation Cooler with strap
Fermentation Cooler with strap

Cool Brewing Fermentation Cooler product review

Fermentation Cooler by Cool Brewing LLC
Fermentation Cooler
by Cool Brewing LLC

Whilst attending the National Homebrewers Conference 2014 in Grand Rapids, Michigan, we met with a number of product suppliers at the Homebrew Expo including Cool Brewing LLC. Cool Brewing were showcasing their Fermentation Cooler which is “an inexpensive and easy solution to keeping your homebrewed beer fermentation temperatures in control”.

Why is temperature control needed?

Temperature control during fermentation is an essential part of turning out a good quality homebrewed beer. If the temperature is too low then the yeast may settle, or flocculate, to the bottom of the fermentation vessel and cause the beer to not fully ferment out and reach the correct terminal or Final Gravity (FG). The act of yeast fermentation generates heat and without external control the temperature of the wort can rise too high and cause the yeast to produce off-flavors.

Temperature-controlled freezer
Temperature-controlled freezer

Lagers require lower fermentation temperatures, usually 45-55 deg F (7-13 deg C) whilst Ales require higher fermentation temperatures, usually 59-72 deg F (15-22 deg C) depending on the beer being brewed and the yeast being used. Without some method of controlling the temperature it may not be possible to reach and/or maintain the desired range relative to the ambient temperature which can fluctuate depending on the time of year and geographic location.

It is possible to overcome some or many of the above issues by varying which beers are brewed  based on the seasonal temperatures (e.g. lagers in the winter and ales in the summer) and where fermentation is carried out (e.g. in a basement, cellar or garage).

That being said if you live in a warm climate (or it is during the summer) and you want to lager a beer then temperature control will pretty much be essential in order to lower the temperature gradually by 1 or 2 degrees per day to just above freezing then hold it there for 4-8 weeks.

Typical cooling options

There are a number of solutions that homebrewers use for temperature control with varying levels of success, convenience and associated costs:

  • Wet towel or t-shirt – this involves covering the fermentation vessel with a wet towel or t-shirt and standing the fermenter in a tray of water so the towel/t-shirt remains moist. A household fan is then pointed at the fermenter so the temperature is lowered by around 5 deg F (2-3 deg C) through evaporation. The water may need topping up and this method is inexpensive. The key issue is only being able to lower the temperature by a few degrees.
  • Swamp cooler – this involves sitting the fermenter in a bathtub or large container filled with water and then adding soda bottles, which have been filled with water and then frozen, to the water in order to lower the temperature. Alternatively ice cubes or ice packs can be added and replaced as needed. This method is good for lowering the temperature 3-5 deg F (1-3 deg C). This method is inexpensive but like the above method only allows the temperature to be lowered by a few degrees.
  • Refrigerator or Freezer – this involves the use of a household fridge or freezer (upright or chest) as a cooler compartment and a controller (analogue or digital) which is used to set the desired temperature. The controller has a probe to detect the internal temperature of the cooler compartment and turns the power to the fridge or freezer on when it rises above a certain threshold. This method is good for getting down to just above freezing in the case of a fridge and well below this in the case of a freezer. The downside is the need to obtain or purchase a fridge/freezer and also the price of a temperature controller.

Other more exotic solutions do exist such as building an insulated cooling room fitted with an air conditioning unit.

Cool Brewing Fermentation Cooler

Fermentation Cooler with top open
Fermentation Cooler with top open

At the conference I was kindly given a Fermentation Cooler by Cool Brewing LLC to review when doing my next batch of homebrew. Given that I already have a temperature-controlled freezer I decided to brew a 10 gallon batch of Belgian Blonde Ale and split it into two fermenters to do a side-by-side comparison.

My temperature-controlled freezer uses a Digital Thermostat Control Unit by Johnson Controls in cool mode i.e. it turns the freezer on when the probe detects the temperature has gone above a certain setting and switches it off once that temperature has been reached.

Cooling with frozen 2L soda bottles filled with water
Cooling with frozen 2L soda bottles filled with water

The Fermentation Cooler comes in a box and once opened it is wrapped in a large plastic bag and accompanied by a set of Frequently Asked Questions & Tips. The product comes with a 45 day “no questions asked return policy”.

The cooler is made from black material with the Cool Brewing logo on the front and is cylindrical in shape with the top being 21 1/4 inches (54 cm) in diameter and 26 3/4 inches (68 cm) high. The top has a double zip and inside is plastic lined making it waterproof for condensation or melted ice. On the outside there is also attached a substantial strap but as per the instructions this is not for carrying the item whilst a fermenter is inside.

After the brewing was complete the wort was cooled down using a wort chiller to 64 deg F (18 deg C) with the aim of allowing it to free-rise from the heat generated by the yeast to 66-68 deg F (19-20 deg C). The ambient temperature in the basement is 75 deg F (24 deg C).

Side-by-side comparison

The fermentation bucket was placed in the center of the cooler with a frozen 2L soda bottle of water placed on each side as the instructions said one 2L bottle will lower the temperature by approximately 5 deg F so in theory two would lower it to around 65 deg F.

A variety of ice packs
A variety of ice packs

By the next morning the wort was 57 deg F so the temperature in the cooler had been lowered too far and the partially defrosted bottles were both removed with the aim of waiting until the wort temperature rose to the desired 64 deg F.

Later that day I took a look and the temperature shown on the stick-on thermometer was showing 68 deg F so in order to stop the rise one soda bottle was added back but this dropped the temperature back down to 64 deg F in only a few hours. The next course of action was to stop using the soda bottles as they were obviously too cold for the difference between the ambient and desired temperatures.

Instead I decided to use ice packs which fortunately I had a few in the freezer. Using these meant they could be placed around the fermenter to spread out the cooling effect. This proved to be the best approach for maintaining a steady temperature but it did mean they needed checking and replacing as necessary every 12 hours i.e. morning and evening.

Digital temperature controller
Digital temperature controller

As an aside after opening the cooler it tended to sag but a simple trick to rectifying this is once the zip has been closed just lift the strap and it returns to its cylindrical shape.

The freezer that was being used with the other half of the batch needed some adjustment to the cut-off setting as it tends to slightly over-cool once it switches on but this adjustment was only every other day or so. An improvement I intend to make here is to replace the single controller with a dual controller so it can both cool and heat (via an aquarium heat mat that I use in the winter) as this would reduce the swings in temperature and in theory level it out closer to the desired temperature.

I am hoping that the temperature fluctuations encountered during this learning curve have not stressed the yeast and caused off flavors – time and tasting will tell…


The Fermentation Cooler by Cool Brewing is definitely a cost-effective solution at around $60 and is well insulated. There is however a bit of a learning curve to go through with how much ice is needed to reach the desired temperature and I would expect this will change through-out the year depending on the fluctuations in the ambient temperature.

Fermentation Cooler with strap
Fermentation Cooler with strap

A temperature controlled freezer is more accurate and less effort but this comes at a cost of around $300+ and takes up more space whereas the cooler solution is easy to pack away to save space.

Overall I would say that the Fermentation Cooler is a good solution and should serve many homebrewers well. Next time I decide to brew a lager I will do another split batch and test out how well it lagers at lower temperatures. Same goes for brewing an ale in winter as it will be interesting to see how it can raise the basement temperature from 55 deg F ambient to 65 deg F fermentation temperature.

If you are interested in finding out more about the Fermentation Cooler, you can contact Cool Brewing LLC at www.cool-brewing.com.

Got any other tricks or methods for temperature controlling a fermentation as we would love to hear from you? If you have any questions or comments about this article please do not hesitate to leave them below.

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