Following up on the previous two blog posts, this will be the final post on the properties of beer and how to determine them.
A typical biochemistry test is to determine the bitterness of the beer. The bitterness is dependant on the used hops. Hops contain Iso-α-acids which is the organic component that determines the bitterness. To determine this we use a ultra-violet spectrophotometer. Each specific compound has a specific absorbance of light. Light consists out of an entire spectrum of colours, each having their own specific wavelength. The absorbance of the Iso-α-acids is 275nanometers. This is light we can’t see with our bare eyes as our visual spectrum ranges from 400-750nanometers.
These bitter-acids are extracted out of the beer by adding iso-octane. This component absorbs all the bitterness out of the beer. Because of the different densities, the bitter phase floats on top of the beer. This top layer which contains the bitter components can be extracted. After measurements in the spectrophotometer we get a measurement for the turbidity which is directly proportional with the amounts of bitter-acids in the beer displayed in ppm (parts per million).
Another very important parameter is the turbidity. Whether a beer is see-through or turbid depends on the yeast in the bottle. Often, breweries will use secondary fermentation or fermentation in the bottle which means that a small amount of living yeast cells is placed in the bottle together with the beer. This has a couple of advantages, firstly, as the yeast cells are alive, they use up the small amount of oxygen in the bottle for their own respiration while producing extra carbon dioxide. As oxygen produces off flavours in the beer the yeast cells allow the beer to have a much longer shelf life (3-4 years) in comparison to non secondary-fermented beers (6month shelf life). Secondly, the yeast in the bottle matures the beer over time giving it specific flavours necessary to perfect the beer.
The turbidity is measured with a turbidity meter. It sends a ray of light through the bottle at a 100% intensity. Depending on the turbidity in the bottle, the light ray gets reflected, lowering the intensity of the light ray, and is measured on a sensor at the other side of the bottle. Depending on the decrease of the light intensity the turbidity can be calculated. A brewers wish is that the yeast sticks to the insides of the bottle, this indicates good yeast. A certain amount of turbidity can be wanted but too much is never good. It won’t do you any harm but will cause a bit of stir in your intestines after a few beers. So often the turbidity is measured once when the beer is at rest and once after making a few gentle pouring movements with the bottle. If there’s much more turbidity afterwards then you know that the yeast doesn’t stick to the bottle.
As 2016 comes to an end so does this blog. After reading through this I know for sure that many of you will be able to craft a perfect and delicious beer. Happy holidays and I’ll raise my beer on a good and prosperous 2017. Cheers! “dif-tor heh smusma” as Spock would say or “live long and prosper”.
~Blanckey the Brewer, signing off.