Störtebeker Craft Brewery turns to GEA’s innovative technology for the cold extraction of hop oils

Processing hops with care in the cold block

The factors in hops that make or break a beer are lupulin as well as the hop resins (alpha and beta acids) and hop oils it contains. During the boiling that is part of the brewing process, the alpha acids transform into iso-alpha acids, which bring out the beer’s bitterness and are used as a gauge of its International Bitterness Units (IBUs). But hops can do so much more. Very special aromas come from the hop oils extracted from aroma hop varieties. Hop oils are volatile and are lost at excessively high temperatures. That is why aroma hops are not added to the beer wort during boiling. Instead, the hop oils are added during a second step, namely dry hopping. This process of dry hopping, sometimes referred to as “cold hopping,” is mainly associated with craft and specialty beers.

Resource-efficient, dynamic dry hopping in the cold block

In classic dry hopping, hop cones or pellets are placed in the storage tank, where they remain until the end of storage. However, this static process hinders extraction efficiency because the hop particles sink to the bottom of the tank, which means they have less contact with the extraction medium, i.e. the beer. With hop pellets, there is also the risk that they may not disintegrate fully. Removing the hops at the end of the process is especially challenging for brewers and causes substantial beer losses, as the centrifuges used in the subsequent stage are not usually made to handle the high remainder of solids. In the industry, beer losses of 10 to 20% depending on the specific hop dosage are common. 

“With the HOPSTAR® Dry, GEA has developed a process that significantly improves extraction efficiency – by 30 to 50% compared to a static process,” says Isabel Osterroth, the product manager responsible for fine-tuning the GEA HOPSTAR® Dry. The key is using dynamic extraction in an extraction vessel, where the pellet hops are first fully suspended by a low-shear agitator and kept in motion via pumping. The solids are separated during a sedimentation step, keeping them in the extraction vessel. An additional fine filter catches the finer particles which do not sediment out. This means that only minimal solids are transferred to the cylindrical-conical tank (CCT) and beer losses due to pellet solid sludge are kept to a minimum. Extraction and sedimentation can be repeated in variable cycles, giving the brewer excellent control in terms of contact time and extracted hop oil fractions. The process is carried out in a CO2 atmosphere to avoid oxidation, which results in a more homogeneous product.