DIY STC Fridge Controller

One of the most important elements to improving your home brewing is being able to control the temperature of the fermenting beer. If the fermentation gets too hot the beer may not clear properly and the yeast can produce esters and other by-products that create nasty off flavours in your prize brew, or if it drops too low the yeast can go dormant and fermentation can stall or stop completely. Some beer styles call for hot or cold fermentation however you really want to be able to control this process so you can accurate hit the temperatures you are looking for. In the last couple of brews I made the FV’s were left to the mercy of the natural air temperature in the brewery and as the English summer kicked in and temps hit 25C (and occasionally even higher) they both fell foul to the symptoms of stressed yeast.

I vowed this wouldn’t happen again and therefore it was time for another DIY project! It is common practice for homebrewers (or aquarium owners it seems) to use a STC-1000 to control their temperatures. Without going too much into the detail as to how they work, an STC-1000 will monitor the temperature through it’s probe and if too cold will power a heater circuit or too warm will send power to a cooling circuit. It was up to me to build those circuits though!

The shopping list:

  • 220V STC-1000
  • 3 20mm IP68 Weatherproof Cable Gland
  • Plastic Electronics Project Box (216 x 130 x 85mm)
  • 2 Trailing Mains Extension Sockets
  • 15 AMP Block Connector Strip
  • 13 AMP Fused 3 Pin Plug
  • 1.5mm 3core Flex Cable
  • 1ft Electric Tube (Greenhouse) Heater
  • Under-counter fridge


  • Wire snips/strippers
  • Dremel/drill & hacksaw
  • Small Flathead Screwdriver
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The bits

The total cost of the bits above was about £70 but this included the £20 fridge from ebay and the Tube Heater. The cost of the STC box and cables etc was more like £35 and again I used UK based ebay sellers so with a little more research or waiting it would be possible to bring this cost down further.

  1. Cut the holes in the project box and fit the STC and three Cable Glands. I also drilled a 6mm hole to pass the probe through. The Dremel made this job a doddle compared to the drill and hacksaw approach I took to the DIY Stirplate!

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2. Pass the 3 core cables through the glands into the box then remove the outer cover to allow easier wiring. I used the following wiring diagram off the internet however take care because on some STC models the Heating and Cooling circuits are the other way around!

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The instructions!

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All wired up!

3. Close up the box, assemble the plugs and sockets on the cables and plug it all in!

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4. Once the build is complete the probe itself needs to be calibrated against a known temperature such as boiling water or in my case I used a thermometer that I had already verified as accurate.

The STC has 4 settings:

  • F1 – Temperature Setting
  • F2 – Temperature Variance Setting
  • F3 – Compressor Delay
  • F4 – Probe Calibration Value

I won’t go into too much detail here as you will really need to set this to your own personal setup and preferences but in brief the settings are as follows:

  • F1 is set to the temperature you require (19C in my case for fermenting an IPA).
  • F2 allows you to define how accurately you want the STC to get to that temperature. For example a setting here of 0.5 degrees will send power the cooler when the temperature reaches 19.6C, a setting of 0.2 will turn the cooler on at 19.2C.
  • F3 controls the delay in turning the fridge compressor on and off. Rapid switching the compressor on and off can reduce its working life, a setting of 3 minutes is pretty standard here it seems.
  • F4 allows you to calibrate the probe. I found that the default probe was reporting 3.5C lower than my trusty thermometer so if I set my STC to 19C with no corrections I was actually only holding a temperature of 15.5C inside the fridge! Not ideal for fermenting beer! This was corrected by setting F4 to -3.5 and now 19C is actually 19C!

And that’s all there is to it! Other than the wiring which was a little fiddly this is a very simple project to build and should make a big difference to the quality and consistency of beer I produce.



Again I should point out that I am not a qualified electrician! Please be extremely careful if you chose to follow these instructions and remember beer/water and electricity don’t mix!




Brewday 30: Jasmine IPA

Brewed 28/08/15

This brewday was inspired by the Additives for Flavour page on and also because I really wanted to brew a special beer in tribute of my new daughter! As soon as I saw the dried Jasmine flowers I knew it was a sign and after a little interweb research the Jasmine IPA was born!

The recipe for the Jasmine IPA:

  • 5.5kg Maris Otter Malt
  • 250g Munich Malt
  • 150g CaraPils Malt
  • 35g Chinook hops @ 60 minutes
  • 41g dried Jasmine Flowers @ 10 minutes
  • 45g Amarillo hops @ 5 minutes
  • 15g dried Jasmine Flowers @ 0 minutes
  • 15g Amarillo hops @ 0 minutes
  • 1 tsp Irish Moss
  • 1 packet US-05 yeast

I was aiming for around 6.3% deep golden American IPA and hoping for the Jasmine to come through on the nose. I had read that too much Jasmine could make the beer taste like washing up liquid however there was no indication as to just how much was too much! Let the guess work begin!

This time I even remembered to take some photographs of the brewday!!!

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The brewery!

Mash completed.

Mash completed.

Jasmine flower additions at 10 minutes

Jasmine flower additions at 10 minutes

Boil completed.

Into the FV. 1.5 litres under target volume.

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1.054 OG, 8 points under target OG

With both OG and volume under target this time around there is some definitely amiss with my Beersmith settings. This’ll need tweaking before brewday 31!

Looking forward to trying this one in a couple of weeks!

Brewday 29: Brewers Gold II

Brewed 10/07/15

For this brewday I followed the current trend in Hollywood and decided to re-brew a previous recipe with a few tweaks rather than coming up with a new one myself! This time it is my Brewers Gold clone, but with different hop timings to try to really bring out the flavours without using the hopback (as this was a last minute brewday!)

The recipe for the Brewers Gold:

  • 2kg Maris Otter Malt
  • 2kg Lager Malt
  • 270g CaraGold Malt
  • 30g Brewers Gold hops @ 60 minutes
  • 30g Brewers Gold hops @ 15 minutes
  • 40g Brewers Gold hops @ 1 minute
  • 1 tsp Irish Moss
  • 1 packet Nottingham yeast

Again this write up is another brief one but as this is the last one of this blog amnesty normal service should be resumed from brewday 30!

This one also was over-sparged and volumes were up while OG was down. I will need to check the figures I use in Beersmith as this is becoming a recurring issue! Fortunately the Nottingham yeast used here is very reliable and got the FG down to 1.006 and therefore was bang on target ABV at 4.3%.

Again this one was a little cloudy going into the bottles and keg just as the (not a) Steam Beer in brewday 28 was. It was fermenting in the same area as that brew so I suspect this one was also on the warm side for the yeast. There are no off tastes in either so hopefully this is purely a cosmetic issue for these beers. STC Fridge Controller is the next job before brewday 30!

Brewday 28: (not a) Steam Beer!

Brewed 03/07/2015

This brewday was a perfect example of why you should check your inventory before you set your mind to brewing a particular beer! My intention this time around was to re-brew the Steam Beer I made in brewday 3 however when it came to the evening before brewday I discovered I didn’t have enough Northern Brewer hops (which are the prime hop for this style of beer) or any Californian Common yeast (essential for this style!). As a result I have no idea what this beer is… It’s not a Steam Beer, it’s more a mediumly hoppy American Best Bitter. Odd, but hopefully tasty nonetheless!

The recipe for the (not a) Steam Beer:

  • 4.5kg Maris Otter Malt
  • 500g Medium Crystal Malt
  • 36g Ahtanum hops @ 60 minutes
  • 21g Centennial hops @ 15 minutes
  • 19g Northern Brewer hops @ 5 minutes
  • 1 tsp Irish Moss
  • 1 packet S05 yeast

Another workday mash for this brewday and again a brief write up.

Again I must have over-sparged as the volume was higher than expected and as a result the OG was 10 points or so short on target. Fortunately the yeast worked wonders and the FG was down at 1.008 so ABV was pretty much on target at 5%.

This beer didn’t look the clearest going into the keg even after being cooled for 3 days before racking. Hopefully this will clear during conditioning in the keg but I suspect the fermentation took place at the top end of the tolerances due to the British Summer finally taking hold!

One of my upcoming projects is an STC temperature controller to utilise my spare fridge as a fermentation chamber which will stop this being an issue in the future. Watch this space for the build writeup!

Brewday 27: Irish Red Ale IV

Brewed 15/03/15

Version 4! Surely this time it will be the one that is actually red?? Ultimately the red-ness comes from the amount of Roasted Barley that is used in the recipe and version 2 taught me that 80g is not enough and 3 that Cara malts are not an easy substitute so therefore for this version i’ll go for 110g and cross everything! I also had noticed that the Rauchbier I brewed in AG23 had a distinct reddy hue so into the recipe goes 100g Rauch Malt! This addition should also add a little smoky flavour to the beer which should be a nice touch.

The recipe for the Irish Red Ale today:

  • 4.2kg Maris Otter Malt
  • 200g CaraRed Malt
  • 110g Roasted Barley
  • 100g Dark Crystal Malt
  • 100g Rauch Malt
  • 30g East Kent Goldings hops @ 60 minutes
  • 20g Bramling Cross hops @ 30 minutes
  • 1 tsp Irish Moss
  • 1 packet S04 yeast

As it’s a good few months since this brewday the write up is very brief and there are no pictures!

I’ve chosen to use these workday mashes for all brewdays moving forwards as it works perfectly with fitting brewing into my increasingly busy life!

On this occasion every target point was hit and the finished beer was bang on at 4.7% ABV. Not bad seeing as there has been no brewing for what seems like an age! Most of this batch was kegged straight away (as stocks in the kegerator had run out!) but there are 6 bottles tucked away for the various homebrew clubs to try!