Brewfridge question

[Richard Renwick]

Hi all,
I have been brewing now for 3 years and have always fermented in a cupboard that has a stable temperature of 20 degrees C. But due to excessive geekiness, I decided to make a brewfridge using a raspberry Pi and kit from BrewPi. It's in an old under-counter chest freezer which can heat, cool & has temp sensors in the fridge, the fermentation bin and outside in the room. Now to my question...

I am used to reading temp ranges for yeasts like 18-21C and I have always been happy to stick that into my room at 20C and let it do its thing. However, my brewfridge now has the capability to let me maintain a constant fridge temp OR a constant beer temp. Obviously choosing a constant fridge temp of 20C would be the same as using my cupboard and choosing 20C constant beer temp would meant the brew fridge would cool & heat to try to keep the wort at a constant temp (there is a sensor in the fermentation bin). So my question is, should I try to keep the wort within the temp range given for the specific yeast or just go with choosing a fridge temp in the middle of the range?

Thanks for any advice on this one,
Rich

 

[Bigcol49]

Hi!
This has been discussed at length on this forum.
Here's my two-penn'orth.
The volume of air in the freezer chamber will be smaller than the volume of the cupboard. If your sensor is measuring air temperature it will cycle the heating/cooling circuits quickly.
If you measure the wort temperature, the thermal mass of the liquid will prevent short cycles from the heating and cooling circuits.
Go for a temperature that suits the yeast and the beer that you are brewing. If you are brewing a lager-type beer, aim for the low end of the yeast's range.

 

[Richard Renwick]

Hi!
This has been discussed at length on this forum.
Here's my two-penn'orth.
The volume of air in the freezer chamber will be smaller than the volume of the cupboard. If your sensor is measuring air temperature it will cycle the heating/cooling circuits quickly.
If you measure the wort temperature, the thermal mass of the liquid will prevent short cycles from the heating and cooling circuits.
Go for a temperature that suits the yeast and the beer that you are brewing. If you are brewing a lager-type beer, aim for the low end of the yeast's range.

Thanks for the reply. I did have a quick search and didn't see anything relevant, but I will have a more prolonged search later.
I totally agree with what you're saying regrind the short cycles and indeed is what I see - although the hysteresis is not as bad as I thought it might be thanks to some reasonably clever maths in the algorithms.
At the moment, I am brewing an ale with WLP028 yeast which says 18-21C on the packet (for ales) and so I have asked the fridge to stay at 20 and see what happens. I started it yesterday and the wort started at 17.8 and has been gradually climbing. It is now at 21.2 and still climbing with the fridge at a constant 20 +- 0.5C. This is what started me wondering if I would have been better to ask the fridge to work on the wort temperature to try to keep it at a more constant temp. Of course, with the amount of liquid and the fermentation bin being plastic, I am not sure how good a job it would have done.
Hence I was just wondering what the general views were - it sounds like there is no consensus if it has been done to death on here. I will try to dig out old posts on it later tonight and see what all the discussion points were.
Thanks for the reply :)

 

[F00b4r]

Hi!
This has been discussed at length on this forum.
Here's my two-penn'orth.
The volume of air in the freezer chamber will be smaller than the volume of the cupboard. If your sensor is measuring air temperature it will cycle the heating/cooling circuits quickly.
If you measure the wort temperature, the thermal mass of the liquid will prevent short cycles from the heating and cooling circuits.
Go for a temperature that suits the yeast and the beer that you are brewing. If you are brewing a lager-type beer, aim for the low end of the yeast's range.

The Brew Pi is smart enough to figure out when to stop cooling/heating early enough that you do not really get overshoots. It will also only partially powerr the heater if needed and will measure both wort, fridge and ambient temperature.

 

[Honk]

Seeing as you can measure the temperature of your wort then I would go with that. If you measure the surrounding air temperature also you will notice quite a difference especially in the early days of a vigorous fermentation.
Varies according to what I'm brewing but generally I like to start off towards the lower end of a yeasts recommended range but gradually increase to the upper range (maybe over 4 to 5 days)

 

[Richard Renwick]

The Brew Pi is smart enough to figure out when to stop cooling/heating early enough that you do not really get overshoots. It will also only partially powerr the heater if needed and will measure both wort, fridge and ambient temperature.

Yup, the algorithms are pretty clever. When you look at the graph it looks like it overshoots a lot but when you actually look at the data points, it is only going over and under by 0.23 degrees which is perfectly fine and to be expected :)
I am quite impressed with it so far.

 

[Richard Renwick]

Seeing as you can measure the temperature of your wort then I would go with that. If you measure the surrounding air temperature also you will notice quite a difference especially in the early days of a vigorous fermentation.
Varies according to what I'm brewing but generally I like to start off towards the lower end of a yeasts recommended range but gradually increase to the upper range (maybe over 4 to 5 days)

Thanks for the reply. This is what I think I will do with my next brew. Just for interest, I've attached the graph for the current one where I had the fridge set to a constant 20 degrees. Green is the wort, blue the fridge and grey the room. You can ignore the leftmost peaks as that was me getting things setup.

Thanks again,
Rich

 

[Dutto]

You are starting to overthink what is basically a simple question.

The question is "What does the yeast want?" and the answer is "A stable temperature in the wort."

The way to do this is to stick the temperature probe to the FV so that it measures the temperature of the wort (rather than the temperature of the fridge) and therefore gives the yeast a steady temperature in which to do its stuff.

I use a Wilco FV. To trap the probe against the side of the FV I have a notch cut into one side of a kitchen sponge (where the probe is lodged) and then use the handle of the FV to trap the probe against the side of the FV below the level of the wort.

I then adjust the Temperature Controller and Heater to ensure that the temperature of the wort doesn't fluctuate by more that about 0.3*C; which is well within the ability of the Controller.

 

[Dutto]

......... I had the fridge set to a constant 20 degrees. Green is the wort, ...........

The rising and falling temperatures in the wort is caused by the fermentation activity of the yeast. Strapping the controller to the FV keeps the wort at a steady temperature regardless of yeast activity.

 

[IainM]

I think it depends on what you want to make. Keeping the temp of the wort constant will keep it clean, and I remember reading one comparison of temp controllers in which the pinpoint accuracy of the BrewPi two-sensor setup, set to constant wort temperature, was blamed for producing a less characterful beer. For a clean beer where you want the malt or hops to shine, then this isn't a problem and is probably a good thing. For something with a bit more yeast character, like and English or Belgian ale, then you might want to let the temperature fluctuate naturally a bit more. In Stan Hieronymous's book on Belgian beers, he says that the traditional Belgian breweries let the temp free rise quite dramatically, and if any beer is dominated by yeast character then those are.

 

[Smileyr8]

Right here's what I do. I tape the temperature sensor to the outside of the fermentation bucket using duct tape then tape a sponge over the the sensor this then theoretically is reading the temperature of the wort on the bucket without actually taking the risk of introducing anything that may be on the sensor into my wort.

 

[Ghillie]

I'm seeing a lot of excessive rabble on this matter... No offence guys.

Pick a happy medium fermentation temp and give it a differential of 0.5C. Mine is 19.5C for ales.

You won't have overshooting problems if your probe is fixed to the side of the FV and insulated from ambient air.

 

[IainM]

The OP is looking for specific advice about the BrewPi setup, which has two temperature probes, one for the fv and another for the fridge, and which has a self-adjusting algorithm that dynamically alters the temperature of the fridge so that the temperature of the wort stays where you want it to be. He isn't asking about a simpler one-probe controller.

 

[F00b4r]

I think it depends on what you want to make. Keeping the temp of the wort constant will keep it clean, and I remember reading one comparison of temp controllers in which the pinpoint accuracy of the BrewPi two-sensor setup, set to constant wort temperature, was blamed for producing a less characterful beer. For a clean beer where you want the malt or hops to shine, then this isn't a problem and is probably a good thing. For something with a bit more yeast character, like and English or Belgian ale, then you might want to let the temperature fluctuate naturally a bit more. In Stan Hieronymous's book on Belgian beers, he says that the traditional Belgian breweries let the temp free rise quite dramatically, and if any beer is dominated by yeast character then those are.

Interested to see the actual source on this as I would have thought it more likely that people switching to the Brew Pi are effectively brewing at a lower temperature due to the lack of temperature swings, rather than the actual swings themselves bringing in more character, another reason I have in the past asked brewers about their temperature control when attempting to replicate some amazing beers I have tasted.
By the way their is no current "free rise" setting for the Brew Pi, which seems quite daft but I believe (if I am remembering right) this may come with the new version (easy to get around but kind of ruins the point of the controller for some beers).

 

[IainM]

Interested to see the actual source on this as I would have thought it more likely that people switching to the Brew Pi are effectively brewing at a lower temperature due to the lack of temperature swings, rather than the actual swings themselves bringing in more character.

That certainly seems plausible. I've just had a quick search but I can't find it. If I remember correctly, they compared three temperature controllers, logging the wort temp then tasting the beer. The first two were comparable and resulted in a degree or two of swings, but the brewpi kept it within 0.2ish degrees throughout, and was less characterful.

EDIT: <sarcasm> I think the free rise setting is also called 'off' </sarcasm>

 

[Richard Renwick]

You are starting to overthink what is basically a simple question.

The question is "What does the yeast want?" and the answer is "A stable temperature in the wort."

The way to do this is to stick the temperature probe to the FV so that it measures the temperature of the wort (rather than the temperature of the fridge) and therefore gives the yeast a steady temperature in which to do its stuff.

I use a Wilco FV. To trap the probe against the side of the FV I have a notch cut into one side of a kitchen sponge (where the probe is lodged) and then use the handle of the FV to trap the probe against the side of the FV below the level of the wort.

I then adjust the Temperature Controller and Heater to ensure that the temperature of the wort doesn't fluctuate by more that about 0.3*C; which is well within the ability of the Controller.

Thanks, this makes sense and for the next brew I will get it to use the FV temperature as the one to keep constant. :)

 

[Richard Renwick]

Thanks everyone for the views and comments. I think what I am going to do is make another batch of the same beer as the one that is almost finished fermenting and for the 2nd one I will ask the BrewPi to keep the wort at a fixed temperature and then compare it to the current beer that was with the fridge constant.

Thanks all :)

Rich

 

[skulltat280]

Maybe I'm missing something but if the probe is sanitized why is it a risk to put it inside the FV through a grommet?

Genuine question as I'm interested

 

[Dutto]

Maybe I'm missing something but if the probe is sanitized why is it a risk to put it inside the FV through a grommet?
........

Three reasons:

1. The black plastic insulation on my probe "wiped black" when I removed it after the required two weeks so it looked as if it didn't particularly like the environment of fermenting wort!
2. Putting the probe into the wort (even through a grommet) gives another channel for bacteria to enter.
3. And the main reason - there is no need to put the probe into the wort.