Lesson in what fermentation temps CAN do.

[gunhaus]

You see a lot of posts/questions about fermenting at ambient room temps, and what can be expected without temp control. Allow me to relate some info about a ferment i have going right now that shows just what CAN happen in a good healthy ferment.

A few days ago, i brewed an old favorite stout - a brew i have made dozens of times. I put this to bed in a Spike CF5, attached my temp controller to the heat element, dumped the blow off tube into a bucket of star san, and went away. The garage where this sits is unheated and pretty much runs close to outside temps or a shade above. Much of this winter it has been a struggle to help the heater keep ferm temps UP to 62-64 degrees. (It has been handy for cold crashing though! Just unplug and walk away) But we had a little warm up, and the garage is/was sitting about 42-43 at the time i pitched. Pitch temp was 62. Controller is set at 62.

About 2 and a half days in, I went out to give it a quick check, and as expected the Notty fueled brew was bubbling away furiously. Room temp is still 44 degrees, and the temp on the controller reads 72.4!

Two more days in and the temp reads 72.8.

First, i could have hooked up the cooling coil and brought it down. But 55-60 hours into active ferment i did not see the point. Besides I have brewed this stout with Notty at 72-74 on purpose in the past, and i know that 3-4 weeks in the keg following two week on primary and it will be a very very tasty brew - so no harm no foul in this case.

BUT - there are brews/yeasts where this could have been a real issue. And that is the point i want to make. It is really hard to judge just where your ferment will go temp wise in relationship to ambient room temp. THIS is a bit extreme (Enough so I did check with a couple other temp controllers to be sure!) But it is an example of WHAT can happen inside a lively ferment. And it shows how difficult it really is to say, "my basement sits at 55. so . . . " "Or i have a closet that always holds 62 . . . " Etc. I am 30 degrees above room temp! Based on past experience I would expect the heat unit to run very little in a 44-45 degree room to maintain 62-62 in the fermenter during the first few days of a really active ferment. 16 -22 degrees ABOVE ambient room temp is not uncommon with my set up.

Just food for thought.

 

[MrHadack]

In most people's experience it's not uncommon to see anywhere from 5 to 10 degree temps above ambient, depending upon the OG and the yeast strain. I typically can make a judgement on ambient temps required based on style / yeast. For example, I have a favorite recipe for a Belgian Strong Dark that I do quite frequently, and just about every time I do it (same OG and same yeast strain) I reliably end up 8 degrees above ambient on the fermentation. 64F ambient gets me exactly where I want every time. Happily, this is my basement temp for most of the Autumn and late Spring.

When dealing with a new recipe or yeast strain it's a crap shoot. I just make an educated guess on a range, and then skew toward the lower end. Even still I get surprised sometimes. I just did a California Common using Wyeast 2112. My basement temp was hovering around 60F. This beer should be fermented warmer than a typical lager so I thought about leaving it in the basement at 60F. Ultimately I decided I'd go lower and put it in the chest freezer at 52F. A couple days later I checked the internal temp and it was 61F! This strain was 9 degrees above ambient! I would have been too high if I had just sitting out in the basement. I got lucky with that one, but I definitely made notes about it in my brew book for the next time I use that strain.

 

[Jtk78]

I wonder if the delta between ambient and fermentation temperature will not be greater the lower the ambient temperature is.

To clarify using the example of the California Common above, @MrHadack saw a 9F difference with an ambient temperature of 52F. Had he placed it in the 60F basement, may it have peaked at 67F, or a 7F delta.

I have to admit, I've never seen or heard of a 30F delta as noted by @gunhaus above. Of course we know yeast strains behave differently, and sometimes un-predictable.

 

[gunhaus]

I have never seen it before either which is why I double checked my equipment. And this was my point - it is simply unpredictable. 5 day in and with the bulk of fermentation done, the temp came back to earth as expected, and now the heater is running on and off to maintain the original 62 degree setting. I would say 6-10 degrees is pretty normal. But as i said above a really active lively ferm can go 16 -20, and i have had that happen several times.

 

[BrewnWKopperKat]

For some people starting out, fermentation temperature control seems to be the last 'core' priority that they address.

It's been a while since I've look at starter kits (do the starter kits offer examples for how to do temperature control?) or reviewed introductory chapters in home brewing books (do the books offer ideas for how to do temperature control?) or searched online for resources on how to do temperature control (are the various techniques accurately described somewhere? has a 'trusted' source already reviewed and cataloged them?).

If the information doesn't already exist, maybe a 'sticky' thread at the top of this forum?

Using an extreme example (30 degrees fermenting in a garage) may not be effective as they believe that their closet or their basement is more stable than a garage. And their environment is likely 'more stable' -- but is it 'stable enough'? Is the combination of ambient temperature, air flow, and FV able to remove enough heat from the active fermentation to keep the wort temperature in a good range?

That being said, over the past three years, I've confirmed that I have a place in my house where ambient temperature is both stable during fermentation and predictable. Ambient temperature does change with the seasons (but not in immediately obvious ways) - so there are time periods when I don't ferment at ambient temperature. FWIW, when I ferment at ambient temperature, batch sizes are in the 1.25 gallon range. When I measured internal temperatures a while back for these batch sizes. I saw a 1-2* F difference in temperature (US-05, and I would assume that some yeast strains could go a degree or two higher).