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.