Tuesday, October 4, 2011

The Heisenberg Beer Principle. OR: Why tape is important for beermaking

I don't like lagers. In all the lagers I've ever drank (and I've drank quite a few) I've only found one that I really like (Libira's Double Pils, for those wondering). But as a rule, I don't like lagers. The only reason I'm making a lager now is that my wife is nine months pregnant.

Lagers are good for late pregnancy brews because they have two qualities: One, they are meant to be forgotten in a fridge for a while - so if you suddenly find yourself in the hospital on bottling day, no big deal. And two: While the fermentation refrigerator is maintaining lager temperature, the freezer drops well below freezing (not always a guarantee at ale temps) so your wife can store frozen meatloaf and chilli in there to have in the couple of weeks after the birth when no one has energy to cook. So I gladly volunteered my freezer for this, and heroically brewed a lager as my humble contribution to the baby making effort. ;)

Problem is, I have a fairly old fermentation fridge. I got it in the market, probably after it was cast out by someone who decided it wasn't good enough to keep around anymore. On an average day, this is fine. A fridge doesn't have to work as hard to maintain 18C as it does to maintain 4C, so this isn't an issue. But when you make a lager, you ferment it at around 11C and then you let it sit (lager) for about a month at 4C. I did some field testing with the fridge and saw that it can hit about 5-6C. So I figured that would be fine. (Palmer says that you can lager at 7C if you wanted, so OK.)

So I made a lager. And I fermented it. I set the temp at about 11C with a spread of .7 degrees, which gives the lager an average fermentation temperature of about 111.4 or so. A little warm (recommended fermentation temp is 10C) but the important thing about lagering seems to be the difference between fermentation temp and lager temp, and I knew that my lager temp will be a little warm, so I wanted to keep the temp spread.

This is where things started to go wrong.
See, the temperature controller that I (and many others in this country) use works by cutting the electricity to the whole refrigerator based on readings from a sensor. You tape the sensor to your fermenting bucket, and when the controller senses that the sensor is cold enough, it cuts the power so that the beer doesn't get too cold. Great in theory, not so good in practice. In practice, it seemed that my beer never hit that illusive cut-off temperature. It seemed that the fridge simply wasn't getting cold enough.

I consulted with a fellow brewer, who advised me to check my thermostat settings in the fridge. I did, and the results where immediate: Within a day the temperature, which had been hovering around 12C, jumped to 18C. Oh, the horror! Luckily, this was in the end of fermentation, so it wasn't necessarily a bad thing (it's often customary to raise the temperature of a lager at the end of fermentation for a couple of days.) But I needed to bring the temp back down. After much research and googling, I came up with a surprising answer: The colder the freezer gets, the warmer the fridge is.

The reason for this has to do with the way refrigerators are constructed. They work by cooling the freezer section, and then drawing cold air from the freezer to cool the fridge section. The colder you set your freezer to, the more cold air stays in it, and the less gets pulled into the fridge, so it gets warmer. Fantastic. Now all I need is to set the freezer to the warmest setting and the fridge will get cold again. Hurra, hurray!

Except that I have all that frozen meatloaf and chilli in my fridge. And it is thaws, I will be the one who has to cook after the birth. Oh the conundrum. At the end I decided that I'm not sacrificing the little energy I will have left for no stinking lager. I set the freezer to a medium setting. Cold enough to be thoroughly frozen, warm enough that some air actually got pulled into the fridge.

So the temperature in the fridge dropped again, but only as far as about 11.8C, as before. I was back to where I started.

And then I had an epiphany: In my efforts to do whatever I could for the lager, I had moved it to a glass demi-john, which was encased in a plastic basket. Being both a little lazy and not wanting to leave the fridge open, I had put the sensor for the temp controller in the basket, touching the glass, but not actually taped to it. Was it possible that the temperature it was sensing wasn't so much the temp of the beer, but the ambient?!? I decided to to an experiment. I fished a bottle of beer from the back of the fridge, thoroughly taped the sensor to it, and put it back in the back.

An hour later, the temp read 10.7
This morning, it read 9, which was what the controller is actually set for.

So now I have a puzzle: What is the actual temperature of my beer? What was the temprature when I was fermenting? What was it when I moved it to secondary? Will it, in fact, actually be able to reach 4-6, now that I've changed the measurement method.

Questions abound, time will tell. I don't have high hopes for this beer. But then again, it IS a lager...

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