An accurate approach to assessing the hop particle size and its filtration behavior during dry hopping

The hop pelletizing is not only influenced by the hop variety and the associated -acid contents, but also by many annual and regional variations. In this context, the particle size distribution of the hop products had a subordinate role due to its main application in the brewhouse with its principle focus on -acid content. But due to a high use of hops for dry hopping and associated large beer losses along with the separation of the hop residues, hop particle size is becoming more important. Thus, the aim of this study was the development of a method determining particle size distribution of hop products (powder and pellets) to assess its impact on filtration performance. Using citric acid phosphate buffer (pH 4.5) with 5 vol% ethanol as a solvent resulted in a similar particle size distribution as in beer. In addition a swelling and disintegration time of 60min was determined for all hop products. The particle size measurement had an average standard deviation of 25.9 mu m (Dx(50), n=180) with a confidence interval of 3.78%. The comparison of average particle size (Dx(50)) and filtrate flux resulted in a significant correlation (r=0.846, P<0.001, 58 investigated hop products), whereas hop products with a higher average particle size had a higher flux. Therefore, the method allows the investigation of hop products for the use in dry hopping to achieve optimal filtration performance and low beer losses. Furthermore, the pelletizing process can be examined to produce separate products for application in brewhouse or fermenting and storage cellar.