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-   -   Fermentation Temps - Room Temp vs: Internal Bucket Temp (http://www.homebrewtalk.com/f13/fermentation-temps-room-temp-vs-internal-bucket-temp-291344/)

mccumath 01-03-2012 05:54 AM

Fermentation Temps - Room Temp vs: Internal Bucket Temp
So most of us understand the need for maintaining appropriate fermentation temperatures when our beer is happily eating the sugars in our wort. However, I (and I am sure many others) have a question regarding temperatures and how to handle them appropriately.

Let me give you my situation, then explain my question.

I understand that fermentation is an exothermic process, and that the reactions that are occurring in my fermentation vessel can cause an increase in internal vessel temperature.

Many of the recipes that I have been following give a temperature at which to ferment at (i.e. currently EdWorts Haus Pale Ale - 68 degrees for 10 days). I set my spare bedroom thermostat at about 67-68 degrees, and have an external thermometer that I check a few times a day to see if it is maintaining an appropriate temperature (which it is). I also have a sticky thermometer that is stuck to the side of my fermentation bucket that is actually quite representative of the temperature in the bucket (which has also been tested by other members of HBT - see appropriate threads). My stick on thermometer says that the bucket temperature is about 72-74 degrees.

My question for you more knowledgeable folks out there:

When a specific temperature is specified for fermentation (i.e. 68 degrees), are we speaking about ambient room/fermentation cabinet/fridge temperatures, or are we speaking of internal vessel temperatures? I understand that it is "relatively assumable" that fermentation temperatures >70 degrees can cause undesirable flavors in beer, but if my ambient room temperature is 68 degrees, it is inevitable that the internal vessel temperature is going to be >68 degrees due to the exothermic reactions... Therefore, do I need to decrease my ambient room temperatures, or leave it as is?

I apologize for the wall of text, but I take great care in attempting to provide all available information regarding my questions so that it can be answered more easily.

I also understand the "RDWHAHB" concept, and I also understand that I will "make beer," but as a home brewer, I strive to make the absolute best beer possible with the knowledge/equipment available to me at the current time(s).

I appreciate all of your feedback, and hope that information given in the responses will be of help to me and others on the site. If you have any questions, please ask.


Ryan M.

emjay 01-03-2012 06:16 AM

Ferm temps generally do (and should) refer to the temperature *inside* the fermentor.

Unfortunately, the difference between internal and ambient temps changes throughout fermentation, so simply setting the ambient temperature a certain amount lower than the desired ferm temp is far from ideal, since it will cause the ferm temp itself to start around that ambient temperature, climb to a peak of 10 or so above ambient, and then drop back down to ambient. The last part is especially critical because it's at the end of fermentation, when conditions are less hospitable for yeast, only the most complex sugars are left for them to eat, and they are most likely to stall - in other words, the exact circumstances where a drop in temperature is the *last* thing you want, especially at a temp which is (by design) much cooler than the ferm temp you.considered ideal. In fact, many people prefer to increase the temperature as fermentation starts to die down, in order to promote better attenuation.

So ideally, you want to control fermentation temps *directly*, which can be done using an electronic temp controller that has a sensor measuring the actual ferm temps, either by placing it directly in the wort, inside a thermowell, or - what is probably the most inexpensive, versatile, and popular method - simply taping the sensor to the outside of the fermentor and covering it with PLENTY of insulating material. With the sensor measuring internal temps, cooling will kick in when the beer is too warm (or heating when too cool, if necessary), allowing you to keep it at a very stable temperature the entire time.

mccumath 01-03-2012 01:36 PM


Thank you for the detailed response. I have the ability to control fermentation temperatures both ambiently and internally, using the taping the sensor to the bucket trick. Unfortunately I have no thermowells at this time. I have only ever used the ambient control method as I use the temperature controller for my kegerator.

So, I believe a small test is in order... I have the ingredients coming to brew this batch again (as mentioned - EdWorts Haus Pale Ale). After day two of fermenting ambiently with Batch 1, my ambient temperature is 66 degrees currently, and my internal temperature is 73 degrees. Obviously this will even out as the internal exothermic reactions cease.

What I will do with Batch 2 is brew as normal, and use the temperature controller to see if I can control temperatures more accurately and attempt a side by side taste test. Seems like a win/win situation to me. More beer, direct results!

In regards to your response about insulation around the temperature probe - the probe is stuck directly to the bucket, and then insulated with what? Approximately how much is "plenty"?

Thanks for your help, it is greatly appreciated!

Ryan M.

jusware 01-04-2012 04:03 AM

When you chill your beer, chill it approx 10 degrees below the desired fermentation temp. Set your room (ambient) temp for the desired temp. The fermentation will kick off and drive up the internal temp to match the room temp. Due to the thermal mass of the liquid the temp of the wort/beer shouldn't increase until the fermentation kicks in.

Using a thermowell in the carboy inside a 2 stage fermentation chamber would be ideal.

erikpete18 01-04-2012 07:27 PM

I wouldn't worry about thermometer placement, on that you should be fine. What you may want to consider is using a swamp cooler to maintain a more consistent temp in your bucket. All you need is a rubber bin that your bucket will fit in to (I'm sure there are several pictures of examples on here). Then you can put your bucket in the center and fill it up with water.

The water acts like a heat sink, pulling the heat out of the fermenting bucket and dissipating it to the cooled air. Since water is a much better temp conductor than air, temps will stay much closer to the temp of the water (room temp). You can also toss frozen water bottles into the water for the first week or so to really cool things down. If you really want to get things cold, you can drape a t-shirt over the bucket so that it wicks water up and evaporates or aim a fan at the t-shirt to increase evaporation, further decreasing the temps of the bucket. Using the swamp cooler, you should be able to maintain the temp of your fermentation at or below room temp. Its a little more to clean come bottling day, but not a terrible investment.

weirdboy 01-04-2012 07:41 PM


Originally Posted by emjay (Post 3622344)
what is probably the most inexpensive, versatile, and popular method - simply taping the sensor to the outside of the fermentor and covering it with PLENTY of insulating material.

What I do is put my fermenter in a rectangular cooler and fill it up with water. Then, I control the temperature of the water. It acts like a big heatsink so that your water temp and wort temp are usually very close. At least, that has been my experience previously when taking measurements during fermentation. I stopped putting a sensor in the fermenting wort after the first few times doing this, because the temps were always within 1 degree F of one another.

itrider 01-04-2012 07:57 PM

Thanks Ryan for posting these questions. I was also wondering about this and have been concerned for the past week (my first batch). I have been struggling to keep my temperatures steady...so today, after reading around, I just ordered some items for my next batch. I keep the primary in my basement which has been consistently around 60 degrees. So my problem is the primary getting too cold (first night it did not get warm enough to kick start the ferment process).

I ordered a aquarium heater and pump. I put the primary in a larger can/bucket, fill it with water, then set my heater appropriately to keep the ferment of my next ale around 68-69 degrees (what the yeast of my next batch recommends).

Hopefully this batch will work out and be more controlled.

richlong8020 09-02-2013 06:15 AM

I also had to use the bucket/water bottle trick on this batch. My hardest part is getting the temp down to mid 60s so the water bath can maintain the 68-70 deg temp range. I can barely get to 80 with out ice in the wort.

I'm working on a gravity feed system. It's a 50' coil inside a 10gal igloo cooler. So the boiling wort goes out the spigot, through the coil/cooler, and flows through another spigot into a bucket for primary.

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