German Brewing

Rather than post this in my 'never ending story' of cold fermentation woes, I thought it might deserve its own thread as it may be helpful to others in the future.

How are most people measuring their fermentation temps ? I see Brandon for instance has a sleeve of insulating material, and slides his probe down there to measure the keg wall temp.

I have a thermowell that protrudes into the centre of the fermenting beer, and reads the temp at the heart of it. I constantly take readings of the internal temp, and adjust the ambient carefully to juggle the desired temp. What I have observed, is that there can be a difference between wall temp, and temp in the centre of the liquid, of up to 1C (1C warmer in the centre), or possibly more. My fermenter is about 11 inches in diameter, so quite a bit wider than a corny keg, which is no doubt exaggerating the temp difference between wall and centre.

Prior to attempting the cold ferment method, I had my temp probe stuck to the fermenter wall, under a bunch of foam to insulate from the ambient fridge temp. This previously gave me good results, so I am now questioning the thermowell, and wondering if I should return to a set up similar to Brandon's.

For example, to maintain 8C in the centre of the beer, I need to run an ambient temp of about 6.7C. Obviously the yeast on the outside closest to the fermenter wall will be less unhappy, and progressively happier towards the centre where it is warmer.

What are people's thoughts ?

P.S my thermometer is accurately calibrated.

I ran a few tests while I was getting my setup going. It is entirely possible/likely that fermentation temps are different in the center of the fermentation vs the wall of the fermenter. That said, fermentations have all gone to completion pretty well. One of the next things for me to tackle is fermentation to not just reach FG but also subtly influence flavor. I would like to try a thermowell but out of convenience and an easy solution to get started with I just went with the insulation and probe on the outside.

I believe Bryan uses a thermowell in his fermenters and likely gets more accuracy than me.

Then there's the line of thinking that precision is more important than accuracy and reproduceability is key over hitting a specific actual temperature.

Brandon

Ranco probe directly in a thermowell.

Nick_D, what controller are you using? Ancient, it looks like you're using a Ranco. which is what I used to use. The BrewPi vs Ranco might provide the same level of accuracy, but the BrewPi does great graphing of multiple data points (freezer, fermenter, +1 - room, heater, whatever) along the way. I feel like that gives a more rounded picture and you can 'see' the heat generated by fermentation by the BrewPi adjusting heating or cooling to compensate. Something to consider as I find it to be an order of magnitude better resolution of information.

As an aside, I did a Zero wort aeration fermentation with yeast that was at high krausen and it knocked it down fine. So aeration may not be as much of a factor.

I have SSBrewTech Chronicals and a MoreBeer Conical - both have thermowells. So temp probes inside the fermenting beer. When I use my Spiedels for smaller batches, I tape the probe to the side and expect to set the temp controller slightly lower to account for the delta.

One thing I notice is that you are unable to measure the oxygen content. When I got my DO meter years ago, I was surprised how big the variations can be. For example, not mixing the o2 well enough won't do it much good either. I noticed dead spots, I noticed how easy it is to not provide enough o2 or overshoot.

In short, you are flying blind.

Now, you don't have to have a DO meter. But then you don't have to attempt the advanced stuff either.

For a decent cold fermentation all your variables need to be correct. Before I had a DO meter my attenuation was always lower than when I started to measure and have an idea what was actually going on.

It's time to get the right equipment. Maybe you can borrow one?