mandag 13. september 2010

A beer has fermented out of control

For the past couple of years, we have had the routine of brewing and bottling two brews a week. Recently we have done three, and this week we brewed 4 beers and bottled the same amount. This is quite an achievement, and everybody (and in particular our bottling crew) are pretty knackered.

In the middle of all these crazy days, I just had to take a photo of our Imperial Stout getting out of hand.

When we start the fermentation of a beer, we add yeast. The brewer uses a microscope and assesses the yeast he will use, then he calculates how much yeast he needs to add to this specific batch.

In general, our rule is this: Target is to introduce enough yeast cells to give 1 million yeast cells per degree Plato per milliliter. In this case, the imperial Stout is brewed at 22P, so we are talking 22 million yeast cells per milliliter. As there is 45 hectoliters in our fermenting vessels, a substantial number of yeast cells needs to be added(or pitched as we say). But if for some reason the maths did not work out, or maybe the quality of the yeast was not homogeneous or the observation through the microscope was inaccurate, then the beer can get the wrong amount of yeast pitched.
If the beer gets too much yeast, it will ferment too quick and very aggressively with lots of foam. This photo shows what it looks like in the morning, when a beer has fermented out of control during the night.

Rather messy!

Kjetil P. Jikiun

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