Math, please

Need help figuring out if I ruined my beer. I've posted elsewhere about heating the lager yeast but perhaps this approach might help best.

I have 5 gallons of Baltic Porter in first stages of fermentation with an outside (refrigerator) temperature of 60 degree. The carboy felt cold to the touch, so I'm going to guess the beer was around 64 degrees since there was little activity.

It was going to be a cold night and the fridge is in the garage, so I plugged my carboy warmer into the thermostat set to 60, loosely wrapped it about the carboy (it was touching only on one side) and closed the door.

In the morning the standalone thermometer read the ambient temp at 78 degrees!! I plugged the fridge back in and it's been hovering around 62 degrees.

So. . .if the starting temp is 60-64 and the ambient temperature was rising to reach 78 degrees, what temperature range would I expect the liquid to reach in a 9 hour period?

First basic question..
Did you use lager yeast or ale yeast?
Then we can go from there...
Igotsand

That's a tricky problem to solve. How are you measuring the temperature---where is your thermometer relative to the carboy? Is the 62°F you're measuring with the fridge on the temp while the fridge is running? In my experience, when the fridge is actively pumping heat out, the ambient temperature gets to be a good 10° below the beer temperature after an hour or so. At least, that's what I think my experience is---I haven't paid that much attention to it.

My guess is that, after 9 hours with a heating element pumping heat into the fridge, your beer probably was pretty close to the ambient temperature. I wouldn't worry about it, though, what's done is done. Just get it to the temperature you want ASAP.

[edit] By the way, I did the simplest possible calculation to estimate the temperature swing, and that says you'd reach 78°F after about an hour. The model is not very accurate, but your beer was heating for almost 10 times that time... So, have some math, for what it's worth!

American lager yeast.

I have the carboy in a mini-fridge. The carboy heater was in the fridge and plugged into a thermostat controller with a sensor in the fridge. The thermometer is a desktop model that was sitting inside the fridge measuring the ambient temperature in the fridge. Not sure why the thermostat borked on the heater when it works perfectly for keeping the fridge temperatures at 60, but the carboy warmer was very hot when I opened the door.

A possibility is that the ambient temps in the garage dropped, which brought down temps inside the fridge, and the heater had just kicked on, but this would mean the thermostat sensor wasn't working properly since if it was set to 60 degrees I shouldn't be reading 78.

Not sure what to do since this beer is going to take 3 months to complete. It'd suck to get to the end and find out it was horrible, but I also feel that since the fermentation process was on day two and had only just begun, the fermentation over the next couple of weeks might help clean up off flavors. Perhaps this is just wishful thinking.

Off topic a bit, but isn't 60F ambient too warm for a lager yeast? I would think you'd want the fermentation temperature down in the lower 50s, no?

Lager yeast for a porter? Are you sure?

libeerty said:

Lager yeast for a porter? Are you sure?

Click to expand...

a Baltic Porter is a Lager.

jambafish said:

I have the carboy in a mini-fridge. The carboy heater was in the fridge and plugged into a thermostat controller with a sensor in the fridge. The thermometer is a desktop model that was sitting inside the fridge measuring the ambient temperature in the fridge. Not sure why the thermostat borked on the heater when it works perfectly for keeping the fridge temperatures at 60, but the carboy warmer was very hot when I opened the door.

A possibility is that the ambient temps in the garage dropped, which brought down temps inside the fridge, and the heater had just kicked on, but this would mean the thermostat sensor wasn't working properly since if it was set to 60 degrees I shouldn't be reading 78.

Click to expand...

Well, all this info is good news for you. My model was a worst-case, assuming the ambient was fixed at 78°F and that the beer had infinite thermal conductivity. These are bad assumptions, and the real case will be slower than my prediction: the beer will cool on the outside faster than the inside, which will slow the rate of heat transfer. The ambient temperature will drop when (if) the heater turns off, again slowing the transfer. These additional complications are basically impossible to model accurately with any simple calculation, especially since we don't know what exactly the thermostat was doing.

What I found with my system was that when the fridge was on, the ambient temperature would drop well below the beer temperature. When it switched off, after something like an hour (maybe half an hour), the ambient would have risen back to the beer temperature.

Since you don't have any forced air circulation in the fridge, it's quite possible that the air temperature varies from place to place if the heater is switching on and off. If the thermostat sensor is at the bottom away from the heating element and the thermometer is near (or especially above) the element, it could be that the thermostat was in the low 60s and the thermometer was in a warmer area. Eventually the temperature will equalize pretty well, but it'll take a while.

In your shoes, I'd just run with it. It sounds to me like the beer probably didn't get all the way up there unless your thermostat has failed. Even worst case, it was only at a bad temp for a few hours. That's not good, but lager yeasts do handle being raised up for diacetyl rests, etc, so I'd guess it's not fatal. It'll suck to spend 3 months on the beer, but I think it's a pretty good bet it'll be drinkable.

Thanks for all the feedback!

I contacted Wyeast Labs and described the situation. This was their response:

"Likely the beer will be just fine. This strain is historically used at higher temperatures than you experienced. Also... it is a Baltic porter... so there is a lot there to cover up fermentation mishaps."

So, with that, away I run with it. I'll likely brew another porter or stout just as a backup.