Hops are a key ingredient in beer production, contributing not only bitterness but also to its aroma and flavor. The alpha acid level (AA%) in hops plays a major role in the bitterness they can impart. During boiling in the brewing process, alpha acids transform into iso-alpha acids which make the beer bitter. For this reason, it is important for brewers to know the exact AA value of the hops they use.
Different hop varieties contain varying amounts of alpha acids—even the same hop variety may exhibit different levels. This also depends on factors such as growing conditions and harvesting time. The AA% can vary between 1% up to 20% in hops. Therefore, brewers maintain the consistency of their beer's flavor profile by accurately measuring and controlling the AA content.
This Application Note describes the determination of AA% in hops according to the EBC method 7.4. The hops are first extracted with toluene, then the alpha acid content in the extract is determined through a precipitation titration using conductometric methods.
Dried hop pellets, Solero variety (16% AA)
The hop pellets are first extracted with toluene. For the analysis, an aliquot of the prepared sample is pipetted into the sample beaker and then methanol is added. The solution is then titrated with standardized lead acetate in methanol/glacial acetic acid until after the equivalence point (Figure 1).
The AA% could be reliably determined in hops with conductometric titration (Table 1).
Table 1. Results of the sample determination of alpha acid content in Solero hop pellets.
| Sample | Result wt% | RSD in % |
|---|---|---|
| Solero | 4.5 | 2.7 |
Alpha acid content in hop pellets can be easily determined by using conductivity titration according to EBC method 7.4. A significant advantage over other methods is the robust sensor used for the analysis. It is not influenced by external disturbances and is easy to clean. This quality also simplifies implementing automation of the system.
The pellets’ alpha acid content decreases over time. Therefore, this parameter should be measured again shortly before their use for the best results.
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Internal reference: AW CH1-1116-122011