Fermentation- Controlling your temperature

Fermentation can be a tedious and difficult step in the brewing process for new brewers, and even for the experienced. With a summer in Australia that’s breaking heat records, brewers all over the country have concerns for there precious freshly brewed batches, I’ve seen it all over social media. Perhaps this may be too late for some, but I wanted to share what I’ve learnt so far at keeping your fermenting brew happy, and review my new toy, the Inkbird 308T Temperature Controller.

Usually the yeast determines the fermentation temperature. Generally- Larger yeast 9-14C, Ales 16-22C, some Belgian like Saison like up to 32C, Sours can go even higher. Ideally it would be great to brew with the seasons. Also ideally I’d like to be retired on a million dollar boat in the Caribbean. Temperature swings are the biggest enemy when fermenting beer. A couple of degrees is ok, but big temperature swings low can cause a stuck fermentation (the yeast will become dormant because they’re too cold) allowing the chance for unwanted bacteria to breed. Temperature swings too high can cause the yeasts metabolism to change resulting in by-products that can cause off flavours. Controlling fermentation temperature is mosro important in the first few days when your yeast is multiplying and getting into action.

Let’s look at some ways to aim for the average Ale temperature of 20°C.

If your just starting out and you have a basement, cellar or house that’s always temperature controlled, you are in luck, that might be all you need. These types of areas usually offer a steady room temperature.


If you are on a budget without the above options, keep your beer in the warmer part of the house in cooler months, and the opposite in summer.

Unfortunately, sometimes there is no cool part of the house (like my unit). A simple solution is a Swamp Cooler. Simply place your carboy/container of beer in a bucket of water, and wrap the top of the carboy/container with a soaked towel that makes contact with the water below. You can cool things down even further by adding ice to the water, or by having a fan blowing at the carboy. Be careful when adding ice that you don’t drop the temperature too much.

Swamp Cooler

In an earlier blog I showed you how to build the DIY Aquarium Style Fermentation. This was a fantastic cheap set up for fermentation temperature control in the cooler months, but I have struggled to find a automated way to cool down the water. Without automated cooling it essentially becomes a Swamp Cooler. I quickly grew tired of babysitting my brew with ice and hogging my portable air conditioner so I took the next step to upgrade my fermentation temperature control. However I’m glad I did….

DIY- Aquarium Fermentation

There’s lots of options out there if you like DIY projects (Google- Beer Fermentation Chambers, or Son of a Fermentation Chiller). If you are wiling to spend the coin you can get a Glycol system similar to breweries. Grainfather sell this set-up ready to go. I’ve also seen instructions online how to make a Glycol cooling from an air conditioner (looked a tad dangerous).

Standard for many home brewers is a Fermentation Fridge, but after a bit of research I decided to go with a chest freezer. After reading through a few forums, the main gripe with a chest freezer is lifting the batch of brew in and out, but because my batches are smaller (5 or 10L) it’s not a problem. I picked up my chest freezer for $80 after keeping a keen eye on Facebook Marketplace and Gumtree for a few days, there’s plenty of them on there. As far as chest freezers go it’s on the smaller side (145L), but I’m really happy both with the space it takes up in my unit (minimal), yet I can easily fit 6 x 5L carboys inside, more than most fridges. The other benefit is a chest freezer opens from above meaning the minimal loss of cold air in every time I want to check my brew. Electricity usage is minimal, the freezer only runs for about 30-40 mins a day to keep standard Ale temperature of 20°C during summer.

Of course the freezer by itself isn’t enough unless you want beer icy poles. A temperature controller is required. You can get these cheaper, or even make them yourself, but I was very happy to pay the $49 for the Inkbird 308T Temperature Controller from one of my trusted suppliers at Small Batch Australia. What really appealed to me was the big digital display so I could look over my shoulder from my lounge room into the kitchen, and see the exact temperature of my brew. When it arrived I had it set up within 10 mins of pulling it out of the box, with no previous experience using temperature controllers, it’s that easy to use! It now makes sense why it’s described as a “Plug & Play”


I won’t bore you by going through the instructions, but here’s the link if you want to take a look- Inkbird 308T Instuctions

What I was more interested in before buying, was the Inkbird in action..

The most common placement for the temperature probe are- in the brew itself, but this can cause contamination issues. In a container of water to mimic the brew, but because active yeast causes increased temperature in the brew, I’d question the accuracy. I opted to go with a little Bluetac, covered by a clean chux and then taping to the side of my carboy. If you use this method, also ensure the probe is at or below the level of the brew for accuracy.

Temperature Probe Placement

I set the temperature I wanted at 20°C , with a cooling variance for 0.5 degrees. This means when the temperature hits 20.5C the freezer turns on, the freezer then turns off when the temperature hits 20°C, due to the residual cooling the temperature tends to drop to 19.5°C- 19.6°C, then the whole process starts again as the freezer slowly warms up. I’ve found it takes around 5-6 hours for the temperature to rise back up to 20.5°C, and when the freezer does turn on, it’s only for around 10 mins. Cooling variance is something you’ll have to experiment with initially, with differences in cooling power of your fridge/freezer. Two tips- (1) If your using a freezer- put a piece of cardboard or foam covering the base of the freezer, this will ensure even cooling so your not getting excessive cooling at the bottom of your carboy caused by direct contact with the freezer. Also put the freezer at a lower settings if it’s adjustable, this will avoid excessive residual cooling once it reaches temperature. (2) When you first place your beer in the freezer/fridge, or after adjusting or touching the temperature probe, turn off at the power point for 5-10 mins. You want the probe reading the temperature of your brew, not your warm hands, this will allow the probe to readjust and avoid initial over-cooling.

A clever feature for when that time comes is compressor delay. This means that you can set how many minutes your fridge or freezer has to wait before turning on once turned off. It’s a smart idea to protect the compressor, as fridges and freezers don’t like being turned off and on again in a short period of time, it gives you added protection while your working out the perfect variances.

EDIT: I’ve now added a heat pad inside the chest freezer, it works great keeping the temperature within the set 5 degree +/- variance. At first I places the heat pad under the carboy but since learned it can effect the yeast by getting it too hot. I now just have the heat pad sitting on the side of the freezer wall and it works fine.

I hope I’ve offered at least one or two tips that might help getting your fermentation temperature bang on!

Stay cool 😎…until next time, happy brewing!

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