The Christmas beer and the wit started fermenting pretty fast. I was a bit worried about the lager yeast as it was very quiet and didn't seem to be alive, but not so. The first bubbles in the fermenation lock came after about 24 hours. So the conclusion is that the yeast spends quite a bit of time reproducing before starting off with a more active fermentation.
The wit was alive after just a few hours. As you can see from the picture below it got off to a rather violent fermentation. This happens with certain yeast strains. It keeps building up until the head reaches the top of the fermenter before it comes bursting out, either through the fermentation lock or through the cap. The fermenter is 30 liters, so the headspace is only 5 liters, not much really. I usually leave the cap open and loose, to avoid that something unfortunate should happen. I would hate to see the fermenter clog and then explode, so would my wife I think. Clogging would only happen when there are sizeable particles, like orange peel, in the fermenting beer. It is more a theoretical possibility, but I'd rather be too careful.
The two beers have now fermented for five days, but I plan to let them go on for a little while more before kegging. Usually I let them sit for anywhere between one and three weeks, depending on me being prepared to keg and whether the final gravity has been reached.
The lager is fermenting in my temperature controlled fridge which I keep at a temperature of between 9.5 and 10.5C (9.7C when the picture was taken). The white thermostat that you see to the right can be configured with a temperature range in which it keeps the fridge. From the thermostat there is a small external sensor cord that runs into the fridge.
The wit is fermenting at room temperature, which have been in the range between 20 to 21C the first five days. This is perhaps a tad too high, but the yeast specifications seems to indicate that this is just fine. We'll see. Other wits I've made have been fermenting at 19C.