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Hop and hop substances—Induction, reduction, or suppression of gushing?

ABSTRACT: Gushing refers to the spontaneous overfoaming of carbonated beverages directly after opening a bottle or can. As gushing is still a problem for the brewing and beverage industries, it is of worldwide interest in the technological and scientific fields. After comprehensive research on raw materials over many years, no single substance has been identified. It is generally agreed, that hops have gushing suppressing properties in beer. A suitable hop technology in the brewing process can lead to a distinct gushing reduction. Practical industrial experience has proven that stronger hopping (e.g., pilsner beer) provides a significant reduction in the gushing potential of beer. While developing a new test method to determine the gushing potential of malt, hop could be used. Current gushing tests (according to MEBAK) still use the overfoaming amount of a test-specific carbonated malt extract to determine the gushing potential of malt. Unfortunately, overfoaming amount can fluctuate, so a precise quantitative comparison of malt samples in terms of gushing is difficult. The new concept quantifies the gushing potential of malt more precisely by applying the modified Carlsberg test. As in this method a “zero point” where gushing is neutralized by hops, the problem of fluctuating overfoaming amounts does not exist anymore. In this context the following question is raised: which specific substances in hops are responsible for gushing reduction or suppression? Phenolic acids, like sinapic acid, ferulic acid, cinnamic acid, and vanillic acid, as well as constituent parts of the essential hop oils, were examined. It turned out that some hop substances exist that can cause gushing. There are two possible reasons. 1) Hydrogen bond interaction between phenolic acid molecules occurs intensively. This results in larger molecule interconnections where CO₂ can be released. 2) According to the multi-functional groups CO₂ can directly interact via hydrogen bonds with phenolic acids. The gushing positive effect of phenolic acids could be compensated for by the addition of constituent parts of essential hop oils, where the different monoterpenes myrcene, guaiene, ocimene, and limonene with palmitic acid suppressed gushing, while pinene and linalool with palmitic acid have only a gushing reducing effect. The high fugacity of constituent parts of essential hop oils requires measurement in a closed system. With a DSC (differential scanning calorimeter) it could be shown that gushing substances form mixing units while essential hop oil is present. The formed mixing units lead to gushing reduction or suppression. A further indication of mixing unit formation could be observed by applying a shock test. It appears that the mixing units, which suppressed gushing before, could be destroyed by abrupt mechanical agitation; afterward gushing occurred again. The gushing suppression effect of the mixing units was not reversible after several days.

Antonie Herrmann studied food technology at the University of Applied Science Weihenstephan-Triesdorf from 2006 until 2010. Before 2006 she apprenticed as a chemical-technical assistant. In 2010 she wrote her diploma thesis about the stability of the FMD virus at the Inertvet International GmbH in Cologne and started working in 2011 as an assistant in quality control at the same company. Since August 2011 she has been working as a scientific assistant at the University of Applied Science Weihenstephan-Triedorf, focusing her research on protein, colloidal, and particle analyses.