As a sommelier and brewer, I have had the opportunity to learn about the various methods used to measure International Bitterness Units (IBU) in beer. One of the most common and widely accepted methods is through the use of spectrophotometry.
Spectrophotometry is a technique that measures the absorption of light by a substance. In the case of IBU measurement, this technique is used to determine the concentration of iso-alpha acids in beer, which are responsible for the bitter taste.
To measure IBU, hops are typically boiled in the wort during the brewing process. This boiling helps promote the isomerization of the alpha acids present in the hops, converting them into iso-alpha acids. These iso-alpha acids contribute to the bitterness of the beer.
After the boiling process, the beer is cooled down and filtered to remove any solid particles. The resulting liquid, known as the beer sample, is then analyzed using spectrophotometry.
In order to enhance the hydrophobicity of the iso-alpha acids, which are slightly hydrophobic by nature, the pH of the beer sample is reduced by adding an acid. This reduction in pH increases the hydrophobicity of the iso-alpha acids, allowing them to be easily extracted and measured.
Once the beer sample is prepared, it is placed in a spectrophotometer, which emits a beam of light through the sample. The iso-alpha acids in the beer sample absorb specific wavelengths of light, and the spectrophotometer measures the amount of light that is absorbed.
The absorbance of light is then converted into a numerical value, which represents the concentration of iso-alpha acids in the beer sample. This value is expressed in parts per million (ppm) or milligrams per liter (mg/L) and is known as the IBU.
It is important to note that while spectrophotometry is the most widely used method for measuring IBU, there are other techniques available as well. These include high-performance liquid chromatography (HPLC) and gas chromatography (GC), which can provide more precise measurements of iso-alpha acids.
In my experience, the measurement of IBU is not only important for determining the bitterness of beer, but it also plays a crucial role in the overall flavor profile and balance of a brew. As a brewer, I have found that understanding and controlling the IBU level allows me to create beers with a desired level of bitterness, ensuring a harmonious taste experience for consumers.
To summarize, the measurement of IBU in beer is commonly done using spectrophotometry. This method involves boiling hops in wort, reducing the pH of the beer sample, and analyzing it using a spectrophotometer to measure the concentration of iso-alpha acids. This measurement helps brewers achieve the desired bitterness in their beers and contributes to the overall flavor profile and balance of the brew.