Word of the Week : Gravity

One of the fundamental measurements related to brewing is the gravity of the beer you are making. The gravity or “specific gravity” of the wort will change during the brewing process as the yeast ferment the wort into beer.

Before the yeast start to produce alcohol, the gravity, or “Original Gravity” of the wort is mostly a measurement of the presence of sugar in the liquid. This number will give you an idea of the amount of fuel that the yeast have to work with in changing your wort into drinkable beer and make it alcoholic in the process. After the fermentation is complete, most of the sugars are used up and there is considerably more alcohol in the beer. At this stage, you can take a “Final Gravity” reading to determine the amount of work the yeast did and the amount of alcohol that they put into the beer by doing that work. Pretty cool!

Most of the time, the gravity measurements are taken using a floating hydrometer. This device is basically a glass tube that has some led in the bottom of it to make is sink. The hydrometer, when dropped into a sample, will sink to a point and stop. The line that the liquid hits on the scale on the side will give you your gravity reading. Generally you have to offset it based on the temperature of your sample but generally it is not that much.

So, now when you go to the corner store and see the 40oz bottle of Steel Reserve High Gravity Lager, you know what they are talking about. Basically, it is some cheap beer that has a lot of alcohol in it.

Cheers!

Word of the Week - Turbidity

According to the all-knowing Wikipedia, Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air and is considered a key test of water quality. Now that you know that, why should you care about Turbidity.

Well, Turbidity is a key to understanding the color measurement for your beer and why it is the color that it is. One way that beer color can be measured is by using a spectrophotometer to measure the absorbance of light at 430nm nanometers, as it passes through a sample. This method was established by the ASBC as a way of standardizing the color measurement process. At the time, it was measured against colored glass plates and was done manually which allowed for a degree of error. The 430nm of light bandwidth was selected at the time to create a set of results that were consistent with the Lovibond measurement that was used at the time. Thus, the Lovibond and the new Standard Reverence Model (SRM) were used interchangeably.

Turbidity makes its appearance as the cause of less light to pass through the solution, thus creating darker wort and a higher Lovibond/SRM scale rating. This explains why you can actually filter color out of your beer if you use a fine enough filter medium.

There are other ways of measuring the color as well. Many brewing suppliers sell charts that brewers can use to compare beer samples to and get a rough reading of their SRM/Lovibond measurement. I have included a table from http://en.wikipedia.org/wiki/Standard_Reference_Method that can be used in the same way and also shows where various styles fall on the scale.

Hope you enjoyed the word of the week.

Cheers!