My cider will kick your beer's butt!

I made hard cider a couple of weeks ago.
I made cider because brewing all grain is a lengthy process, and I'm not allowed to do it until the baby comes. I brewed a couple of extract beers in the meantime, which was kinda nice (like going back to a family sedan after a long time or riding a motorcycle) but boring. So I moved on to other alcoholic beverages.

Cider is remarkably easy to make. You mix apple concentrate with enough water, add sugar, boil a bit, cool, and pitch. That's it. Of course, never content to do things the easy way, I ended up adding not quite enough water, and added in all the inverted sugar I had on hand (about half a kilo, to an 8liter batch) and so I ended up with cider that had a starting gravity of 1.079. Given that I could expect it to drop to about 1.005 if I let it ferment all the way, I was looking at almost 10% ABV. A bit high for a fruit drink. It would be better if I could stop the fermentation before it went all the way.

One way to stop the fermentation, or at least to dramatically reduce it, is to keep the drink cold, and remove as much of the yeast as you can. Of course, you can't go in there with a sieve and fish the yeast out, but it turns out that if you cool the liquid, the yeast will go dormant and fall out of suspension. Which is a win win situation, if you can get the thing cold enough. 4-5 degrees C ought to do the trick. This is called "Cold crash".

Ah, but there's a problem: My fridge, which has been the subject of much consternation lately, is nowhere near that cold. And given that it is currently fermenting lager, it shouldn't be that cold. What can you do?

Enter the MLCS-7 Massive Liquid Cooling System. Also known as "my mash tan cooler, with about 7 liters of ice:
I have a pretty small mash tan, but my small fermentator fits in it perfectly. I put it in the middle, put as much ice around it as I could (in re-freezable plastic bottles) and topped it off with cold tap water. To carry the heat better I connected my pump to circulate the water from the bottom of the tan back on top. This turn out to be completely unnecessary as, within 12 hours, the temperature of the water dropped to an incredible 1.3 degrees C - my actual fridge doesn't get that cold!

After about 42 hours the cider was so thoroughly cold crashed that it had virtually gone through the floor. I transferred it to a bottling bucket, leaving behind most yeast, added a bit of sugar (totally unnecessary since after the crash it read 1.025, which meant it still had plenty of sugar in it, but old habits die hard) and bottled about 8 liters of golden goodness. It's sweet, eminently drinkable, girls like it, and at 8% Alcohol By Volume it will kick your butt!

As a side note: Heat is energy, and energy can only be transferred, not destroyed. I got a great illustration of this during the cold crash process. I would rotate the ice bottles in and out of the cooler, taking freshly frozen bottles from the freezer, and putting half-thawed bottles back in. As a result, the temperature in my freezer rose dramatically from about 7-8 degrees below to 1-2 degrees below zero, as the freezer worked to dissipate the heat energy that the ice had gathered. Now that I've finished the process, and the freezer doesn't have to deal with the extra heat, the temperature in there had fallen as low as -8.5C. Which is great for trying to lager my lager in the fridge. But that's a different story.

Newtonian Brewing

A word of warning: I have had a rather broad scientific education, and I like physics. The following is a discussion of Newtonian Thermodynamics, observation, energy exchange, and beer. If you don't have the patience to read it, you can skip to the last paragraph, which contains the actual point.
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As brewers, we heat and cool beer regularly. It is part and parcel of the brewing experience, and a major factor in how the beer turns out. It is a most fundamental part of brewing. It is also a lie.

It's a lie because this is not actually what were doing. What we are doing is applying energy to a system in order to affect a change in the energy state of a system. Put simply: We don't heat or cool beer, we do things to the environment the beer is in, in order to make it hotter or colder.

This may seem like a petty distinction, and in the case of heating beer, it generally is: When I put a heating element in a vat of beer and turn it on, I'm heating the beer. (At least in any Newtonian sense of the word). But in the case of cooling the beer, this is actually something worth considering: When I cool beer, I don't take energy out of it. I don't aim a "Cold Ray" at it. I put it in the fridge. I change the temperature around the beer, so that the temperature of the beer changes.

And this is important because when I measure the temperature of the beer, I don't actually measure the beer. I measure the temperature of the environment the beer is in. When I tape a sensor to the fermentation bucket, the reading I get will be an average of the temperature of the bucket, and the temperature around the bucket. It will NOT be the temperature of the beer.

Now presumably if you leave an object in an ambient temperature for long enough, it will end up being in ambient temperature. You can try this with a simple experiment: pour a glass of ice water and leave it on the counter. It will eventually warm to room temperature. So be extension, if you had a thermostat next to the glass that showed the room temperature, it would also show the water temperature, since they end up the same.

But beer doesn't work that way. Beer ferments, and fermentation is an exothermic process - it creates heat. Leave a bucket of fermenting beer on the counter, and it will not reach room temperature, because it makes its own heat.

It gets worse: If you tape the sensor of your thermostat to different spots on the bucket, you will get different readings. This is true because beer, like any liquid, stratifies according to density and thermal layers. Moreover, if you tape your sensor to the lid, which does not come into direct contact with the beer, you will get a reading that's much closer to the ambient temperature than the beer temperature.

Now do a little thought experiment: Lets say that you have beer that is finished fermenting. You fill a bottle with it, put both bottle and fermentation bucket in the fridge, and tape the sensor to the bottle. How close is your reading to the temperature of the beer in the bucket?

The answer is, you don't know. Your bottle may cool faster because it's a smaller thermal mass. It may read cooler because it's further in the back of the fridge, or because glass is a better thermal conductor than plastic. It may read warmer because the curve of a glass bottle is bigger than that of a bucket, so the surface area in contact with the sensor is smaller. You simply don't know.

All of this comes by way of saying something simple: Two days ago, my beer was in secondary fermentation, at temperature of 11.5C. Now it's heading toward lagering, with a temp of 8C and falling. I didn't touch the beer. All I did was to change where the sensor was located. So I don't know what temperature my beer is really in, and what temperature was it before. And it's kind of driving me nuts. :)