Grainfather put out an interesting article on "lagering", but they don't seem to have put it on wide release yet so I can't link it. It came at an opportune time as I'd got my first lager in the cold store lagering. And threw up some interesting facts …
Hang on. What's a hardened "Real Ale" drinker doing brewing and talking about "lager"! Well the world has changed a bit, we are not so bigoted and we don't hold with the narrow minded stereotyped attitudes of the past. So if you are a bloke, grab your dolly, and join in. If you're a lass you won't have a dolly 'cos you used it for target practice with your bow and arrow.
Firstly you can "lager" at much higher temperatures than I thought, and there are advantages for doing so (speed for one). Modern malts don't benefit from traditional "lagering" for months on end, so 6-7 degrees (Celsius) for 3-4 weeks is quite adequate (colder can help harden the beer against chill hazes, but otherwise doesn't gain much … apparently, longer for strong beers). Hum, bet that creates some arguments.
But for me, more interesting is what happens if you do cool lower than 6C (actually I'm a bit embarrassed about not realising it before). We all know cool liquid is denser and will sink into the surrounding liquid. This flow ("convection") stirs up the liquid so the temperature throughout equalises. But below 6C? At 4C water actually starts to expand and get less dense (it's why ice floats). In beer it might need cooling a degree or two colder. So convection comes to a halt. And colder still it begins to rise through the bulk!
So if like me you have cooling coils around (or in) the fermenter (Grainfather fermenters have a sleeve for cooling), cooling less than 6C is pretty much a waste of time. If you have a cabinet (fridge) you can get cocky about how much better it is, but circulation in a cooling keg may be cycling the opposite way to what you might think.
Discuss all aspects of fermentation
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