I am telling you all of this as a way of explaining why it is that even at the dead of winter we leave the door to the porch ajar. And why, consequently, the temperature in our house routinely dips into the teens. Ordinarily, this is not much of a problem: We own a large number of blankets and warm cloths, and we keep the young brew-mistress on us regularly, so we all stay warm. But you can't put a blanket on a fermentation bucket (well, you can, but it wont do anything), and at night when we turn the heat off the temperature in the living room where I keep the fermentation fridge does drop substantially. So if I want to maintain my yeast happy and active, I need to use that other function on my temperature controller and warm the beer.
In talking to fellow brewers about this I came up with several ways you can warm a fermenting beer in a fridge. You warm it in a fridge because it's a small and insulated space that you can easily control, and because if you set your heating and cooling at the same place, you don't have to move the beer when the weather changes.
The first method is to use a space-heater or a blow-dryer. You install the thing in your fridge (preferably instead of the vegetable drawer) and plug it into your PID controller. Simple and straight forward. The only problem is that a space-heater, by definition, is not designed to be used in a small confined space (like a fridge) and requires a free flow of air or it gets very overheated. Plus, there's just something about the idea of putting a heater inside my fridge that sets my teeth of edge. I know people do this, and it works, but it still feels like a recipe for trouble.
Second is using a lamp. A regular, 100W light-bulb can produce enough heat to warm an average-sized fridge. There are two problems with this method. One, it is highly inefficient, since the heat is not directed, you must heat the whole volume of the fridge, which means running the bulb for rather a long time every time you open the door of the fridge. The second problem with this method is that the bulb doesn't just produce heat, but also (or rather, mainly) it produces light. Light is bad for beer. (More precisely, it is bad for the hop oils in the beer). And seeing as most of us use buckets or carboys that are light-permeable, long exposure to light is not an optimal solution.
Third is using a heat lamp. Like this: http://www.petplanet.co.il/product.asp?id=654 This is a ceramic terrarium heat lamp that produces the heat without the light. The downside is that it is fairly expensive.
Fourth is using a commercial product, like this one: http://morebeer.com/view_product/16674/102282/The_FermWrap_Heater Nice and elegant. But requires shipping from abroad.
A nice compromise that we came up with during the discussion is to use a regular light bulb (option two) which is mounted instead of the vegetable drawer, and then covering the bottom shelf of the fridge with aluminum foil to keep light from reaching the fermentor. This is definitely a workable option, as it deals with the one major drawback of heating with a light bulb. However, I feel that this is a very wasteful proposition, since the foil will also reflect a certain amount of infrared (heat) radiation, further reducing the efficiency of an already inefficient system. This is an inherent problem of all of the solutions that heat up the whole fridge space: They heat up rather more air than is strictly required to warm the beer, and are therefore inefficient.
At the end, I've decided to go with option four (the heat wrap). It has several important advantages that, in my view, justify the initial investment:
- It is efficient. At 40W, this this will nonetheless heat faster than a 100W light-bulb, meaning that it not only draws less power, it will also draw it for shorter times.
- It is environmentally independent. I can open the fridge door and let cold air in, and the beer will remain at constant temp. In fact, I can set the fridge temp lower (say to lager fermentation temp) and let a lager ferment in one side of the fridge while an ale is keeping warm right next to it.
- It is scalable. I generally only brew one beer at a time, but this product can actually be used to warm two fermentors side-by-side if I so choose.
- It is portable. I can take it to the basement (where the temp ranges from 12 to 14 degrees in this time of year) and let it keep a fermenting secondary from getting too cold down there.
- It is cheap. At $30 plus free shipping, it is actually cheaper than the terrarium lamp. Luckily I have family who is coming from the States soon and would be able to hand-deliver the thing to my door, so I don't pay for overseas shipping charges.
- It is safe to use in small, insulated environments. MoreBeer actually sell carboy bags you can use to insulate this thing. Makes me feel better knowing that this thing is not going to burst into flames.
- It is made for this application. This may seem trivial, considering how many times we homebrewers bastardize pieces of equipment that were designed for something else to use in brewing (laundry pumps and wort-chillers made out of copper tubing are just two examples of this). But given a ready-made, reasonably-priced, specifically-engineered, product that is built for our needs, I see no reason not to take advantage of it.