Determination of alpha acids in hops according to EBC 7.4
AN-T-154
2024-02
zh
Conductometric titration to test hops for alpha acid content
α-酸是啤酒花中最重要的酿造成分之一。它们对啤酒的苦味和风味有着巨大的影响。α-酸本身并不苦，但热异构化作用会将其转化为α-异酸，α-异酸具有强烈的苦味，从而形成啤酒典型的感官特征。啤酒中 85% 以上的苦味都是由这些异α-酸产生的。根据啤酒花的种类和添加量的不同，啤酒中的异α-酸浓度从 10 毫克/升到 100 毫克/升不等。α-酸的其他转化产物是葎草酮，α-酸在啤酒花加工成颗粒或风干啤酒花的过程中氧化形成。 因此，在开始酿造之前，了解酒花产品中的α-酸含量至关重要。本应用简报介绍了以醋酸铅为滴定剂、甲醇为溶剂、通过电导滴定法测定α-酸的方法。
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