Recently a Winemaker’s Academy member shared this amazing system, that he developed, for controlling the temperature of a wine fermentation. In this post Kurt shares all of the equipment necessary to build this system.

I (Matt Williams) have done some minor editing to convert it from an email to an article but by in large this entire article is in Kurt’s words. Please feel free to ask any questions that you may have in the comments below. Also if you decide to build this system for yourself please share your results in the comments.

The original email included links to equipment available on ebay, however, given the frequency at which items turn over on that site maintaining those links proved to be too difficult. So you’ll have to do some hunting for these components but they should be easy enough to find given the amount of information Kurt has provided.

And now for Kurt’s Temperature Control System:

Kurt's Temperature Control System in action.

Click to see a larger image.

I have been using this system over a year now and have found it to be exceptionally effective in controlling the temperature. I tried a brew belt, but found it impossible to reliably control the temperature (probably because I was using it in an extremely cold winter [for us in England] in an unheated building, and then in a building that was unheated overnight in winter). Of course this only works if the ambient temperature is less than 25° C (77° F), which is not a problem for us in England almost every day of the year (or century).

I remember reading in C.J.J. Berry’s book, First Steps in Winemaking, that the yeast likes a very stable temperature.

With this system, there is still a small fluctuation in temperature, because the fermenter is not completely submersed, but it is typically very small, within a degree or so. (I have my tubs in a building that is not heated overnight, so there is often a very considerable drop in ambient temperature overnight in the winter, so I have given it a very good test.)

Here is a description of the components and comments about the various equipment and prices. I have only included them to complete the list of potential equipment. Many of these items are not strictly necessary, but are nice to have. See the discussion for each item.

Kurt's Temperature Control System

Aquarium Fish Tank 2 Way Air Flow Distributor Splitter Control Lever Pump Valve

These are simply more sophisticated versions of a cheaper plastic T valve. Often individual air-stones have different air resistance, so these allow you to easily adjust the air pressure for each stone, so that they produce an even amount of bubbles on each side of the tub. I only use these.

PVC Tube Clear Flexible Plastic Hose Pipe – Fish, Pond, Car, Aquariums, Air Line

I ordered a 10cm sample size (cut it to 2.5cm length) and found that it fitted perfectly around the thermometer to then fit in the airlock grommet with an airtight seal.

Silverline Flat Bit 13mm 128573 Hand Tools Drill Power Holes Wood Drilling Brace

Essential for drilling gromet holes in the lids of 23L fermentation buckets. After much trial and error, I have 2 kinds of lids. No hole for while stabilizing, clarifying or keeping a sanitizing solution. Two holes while fermenting; one fermentation hole is for the thermometer (in the very center) and the other fermentation hole is for the airlock, best positioned halfway of the radius of the fermentation lid.

19mm PVC Tube Clear Plastic Hose/Pipe – Food Grade – Fish/Pond/Car/Air – 3/4″

The only purpose of this is to siphon the water quickly out of the tub. You need to do this before you rack the wine, else the fermenter will start floating as you rack the wine. You must also remember to turn off the heater and wait for it to cool before siphoning the water out of the tub, otherwise the heater will break and may melt a hole in the tub, as well as short electrically if it breaks and is in contact with water. Don’t forget to turn off the heater beforehand!!!

You could cut a piece of garden hose to do this.

5M Length 13mm (1/2”) OD Flexible Corrugated Bellow Tube Sleeve for Cable

The only purpose of this is to create space beneath the fermenter for the water to circulate. You could in fact use anything that could support the weight of the fermenter and allow water to circulate. I have found this a very simple solution. It is also best if the coil covers the entire bottom of the tub, as otherwise when you go to place your fermenter into the tub, you’ll find the coil may move around and it is difficult to place the fermenter centered on the coil. This is especially true if there is a little water left in the tub after your first racking.

Yellow 42L 42 Litre Large Flexi Tub Garden Flexible Storage Container Bucket New

This can be any watertight container that is sufficiently large to allow enough water around the fermenter. However, I have found these garden tubs to be ideal. The handles are very useful to tie the heater cord around to adjust the height of the heater in the tub. Ideally you want the heater about an inch above the coil with an air-stone nearby and just above the coil to promote maximum heat dissipation from the heater.

25W Tropical Ecotherm Aquarium Fish Tank Heater Stat

At first I miscalculated and bought higher wattage aquarium heaters, 50W and 100W, forgetting that fermentation is an exothermic reaction. When I am degassing the wine I sometimes switch the heater to a 50W heater to raise the temperature of the water to 25° C (77° F) to help remove the carbon dioxide. But this seems to work just as well with a 25W heater.

Super Silent Electrical 220-240V 3W Fish Aquarium Oxygenation Air Pump YB-100

I’ve tried a few different pumps but this is the smallest and quietest. Highly recommended

1 Meter 4mm Clear Aquarium Tube PVC Hose Pipe Fish Tank Air Pump Air Line

You may wish to buy a bit more, especially if you have more than one tub.

25mm x 13mm Blue Bubble Air Stones for Aquarium Fish Tank (10 pcs)

This is a case where buying 10 is only slightly more than double the price of buying one, and I would recommend using two air-stones in each tub. These air-stones also clog up and eventually wear out.

4mm 3-Way Air Line Tubing Joints Connectors Aquarium Fish Tank Plastic DE (10 pcs)

This is a case where buying 10 is the same price as buying one.

One Way Non-Return Check Valve Aquarium Co2 System Air Pump Black (5 pcs)

This is a case where buying 5 is the same price as buying one. These one way valves that prevent water from siphoning from the tub into the electric pump. A safety measure. They need to be installed in the right direction with the clear end to the tub.

Mini Acrylic Pipe U Shape Tube Bend for Aquarium Co2 System Diffuser (6 pcs)

Not strictly necessary, but they make it much easier to control where the air-stone are located inside the tub. If you don’t use them, you find the air-stones rise up too far in the water and are not as effective in circulating the water. Also, it is difficult to get them to sit alongside the bottom of the heater. I have tried several glass “U” tubes to do the same thing, but found I kept breaking them, so these plastic j tubes are are definitely better and considerably cheaper.

LCD Digital Indoor Temperature Meter White And Outdoor Thermometer

Not strictly necessary, but very useful. I use the external probe to monitor the high/low temperature of the water (as the thermometer in the must, only gives you a real time measurement). At a glance you can see if the temperature of the water is not what you expect. Is it too high or low or the high-low variation unexpected?

Unwanted temperatures can result from various causes. Most probable are that you turned the heater off to rack the wine, and then forgot to turn it on. Another important use is when you fill the tub with water.

As I fill the tub with water, I alternate between adding a few liters of hot water with a few liters of cold water, while monitoring the temperature, so that I fill the tub with the correct temperature to begin with. I then check the temperature every few hours or so and adjust the thermostat on the heater.

Once you are satisfied everything is set correctly, you can confidently leave the system for weeks and the temperature will remain within a degree or so.


Essential. I have found the digital thermometers to be inaccurate to a degree or two, so have reverted to glass scientific thermometers, that I believe are individually calibrated. I prefer thermometers that are only in Celsius as they are the easiest to read. The worst are those that show both Celsius and Fahrenheit.

I have found that if you put a small amount of 6mm tubing around the glass thermometer then it will snugly fit into an airlock grommet plug as to not allow the CO2 gas to escape. You can then very accurately measure the temperature of the must near its center. This is the only measurement that really counts. I have found with plastic fermentation buckets that there is an approximate one degree temperature loss through the plastic of the bucket. I have tried the chemical strip thermometers stuck on the side of the tub or fermentation bucket, but have found these too inaccurate for my liking compared to a glass thermometer in the center of the fermentation bucket.

Spare airlock grommet for fitting to fermenting buckets etc.

I am certain these are much more cheaply purchase at your local homebrewing shop (if you don’t have them already).


I have put so much enjoyable effort into perfecting this system, that I am very happy to share it with others who may find it useful. So please test it and spread the word if you think it is effective. I have found the problem of temperature control very difficult otherwise.

  • Juan

    Hi Kurt,
    Fantastic engineering and workmanship!
    I live in Bogota, Colombia, in the Andies Mountains, at an elevation of about 2,500 metres. where the days get warm and the nights cold. Our temperture varies from a high of about 20 celcius to a low of 0 celcius year round. My apartment, as well as most homes in Bogota, is unheated.
    The best system I found to keep a warm carboy stable are a 40w and 60w lightbulb. I use an external wine thermometre to monitor the cabinet’s air temperture.
    I had a carpenter build me a wooden cabinet with removeable shelfs and two electrical sockets.
    Since I also make my own yogurt and bread, I needed a flexible heating system.
    The cabinet rests on two levels of bricks. With the bottom and middle shelf removed, the cabinet interior is high enough for the carboy and the lamp.
    I use the 60w for wines and the 40w for the smaller spaces.
    The cabinet is made from 3/8 inch (15mm) thick wood. The cabinet is 20×20 inches (51x51cm) and 22 inches (56cm) high. I had it made 3 years ago and its served me well.
    I will send Matt some photos.

    • Hi Juan, thanks for sharing your system with us! For the reader, here are the pictures of Juan’s temperature control system.

  • Very good information GMB! It seems like aquarium equipment is well suited for maintaining fermentation temperatures. -Matt