Fermenting multiple batches from 1 fridge - howto + pics

Hi everyone, this build has been discussed in a few other threads but I thought I'd try to do a proper write-up with pics.

Essentially I couldn't decide between a fermentation fridge and a lagering/dispensing fridge so this I think unique approach combines the best of both. Just got it working this weekend.

This pic shows the basic setup. Fridge, plus cardbox for a fermentation chamber. 2 STC-1000s driving 2 fermenters in the chamber.

The STC-1000 controllers weren't hard to wire up. The HOT connecter links to a mains plug, so I can connect a heat belt or aquarium heater, or whatever else. The COLD connecter is switching a 12v power supply, as the aquarium pumps don't need mains electricity.

Inside the chamber is 2x swamp coolers. These are 1 gallon batches in secondary fermentation, but I use this setup for 5 gallon as well.

Each swamp cooler contains...
- The fermenter (in this case 2x growlers)
- The temp probe (although if these were in primary I would have the probe in the beer)
- The heat source
- A 12v water pump connected to a hose going to the fridge
- The outlet hose from the fridge

Drilling the hole in the fridge wasn't too hard. I used a grinder to get through the steel, then carefully pulled away the foam checking for internal hoses / wiring. There was none, so I drilled all the way. I poked the 4 hoses through (2 for each fermenter) then padding the gaps with bubble wrap.

Inside the fridge. As you can see 90% of the fridge plus the freezer below is available for regular use as it's not on a temperature controller and will always be 4c / 32f. In my case yeast storage and bottle lagering, plus crash-cooling and keeping my drinking beer cool.

Note the water bucket with 2x mini immersion coils, this is what cools the 2 swamp coolers outside the fridge.

These are the 2 coils which sit in the water bucket. The swamp cooler water is pumped through these coils. Conveniently they also fit nicely inside each other - I didn't want to bend the stainless coil too tight for fear of breaking it.

Inside the swamp cooler. The probe from the STC-1000 sits in the swamp cooler water. This beer is in secondary but during primary fermentation the probe would be in the beer.

When the beer gets too hot the water pump starts pumping the swamp cooler water through the coils in the fridge. I'm yet to test how long this takes but I don't really care if it happens slowly.

When the beer gets too cold (which happens every night where I live) then the aquarium heater starts up and warms the swamp cooler water.

The other swamp cooler, this one is a vienna lager doing it's diacetyl rest. Same deal with this one, except that there is a heat belt wrapped around the bucket instead of the aquarium heater. Works great for these small batches.

This same approach would work fine for a 5 gallon batch as well.

So that's pretty much it.

In essence I am temperature controlling the swamp cooler water. I was originally going to stick the coils inside the fermenters, but there are all kinds of issues with that. Since I do a lot of smaller batches this approach works for 1-5 gallons. It's cool being able to have the temp set independently for each fermenter, since I like to do lagers and ales. I will eventually add a 3rd controller into the mix and have 3 fermantions going from one fridge.

Let me know what you think!

You said that you put the probe IN THE BEER during primary?

Correct. I use a 3-piece airlock and the probe wire bends around the airlock and hangs in the beer, a couple of inches below the surface. This is going to give the best possible reading while the yeast is generating heat in primary. Some people prefer to tape the probe to the side of the fermentor and insulate it, that's fine too, whatever works.

For secondary fermentation I use the S shape airlocks which are better for cold-crashing (they don't suck-back like blowoff tubes and 3-piece airlocks). The probe just sits in the swamp cooler water at this point.

It's probaby not that important for these small batches but in a 5 gallon bucket they hold more heat, and I think you might be off by a couple of degrees if you aren't measuting the actual beer temperature.

I'd be more concerned about putting the same probe that's been sitting in the swamp water ( from the last batch ) into my new batch for primary. I'm sure you do something to sanitize it, but still.
Water is excellent at conducting heat and cold. It's safe to say that your wort will be the same temp as the swamp water ( as long as the swamp water volume exceeds the beer volume). You need enough thermal mass to steer the beer temp, not the other way around.
Anyway , as long as it works for you, brew on!