Investigation of the hops α-acids isomerization and occurring losses of iso-α-acids during wort preparation in the brewhouse

Hop isomerization in the brewhouse is subject to a variety of influences. For breweries it is important to know these influencing factors in order to avoid using an unnecessary amount of hops and thus to save raw material. The aim of the present dissertation is to clarify these factors in their combinatorial effect with regard to wort composition as well as wort treatment and to identify the substance, which binds hop bitter acids, especially iso-alpha-acids, even after wort boiling. In addition, parameter ranges that occur in a novel brewhouse concept and lie outside the conventional brewhouse range are considered. The test series demonstrated that different pH values are advantageous depending on the original gravity. Lower pH values are favorable for higher original gravities, since at higher pH values, the α-acids are more soluble and the resulting protein trub therefore adsorbs more dissolved α-acids. Consequently, these hop bitter substances are no longer available for isomerization. At lower pH values, the trub adsorbs a smaller amount of α-acids due to its poorer solubility. Furthermore, at higher pH values (pH 7.0) an extension of the boiling time from 60 min to 120 min is not economical, since the improved solubility results in an accelerated isomerization rate. The lower the extract, the greater the influence of the pH value. Accordingly, due to the different techniques of the lauter systems and the associated periphery, the boiling times and application times have to be adjusted in order to achieve improved hop isomerization. In concrete terms, this means that the total boiling time increases with the lautering system: continuous mash filtration system < mash filter < lauter tun. A modeling tool [1] would support the calculation of hop application times, amounts and boiling times. Exact knowledge of the wort composition makes it possible to customize hop boiling times and dosages and thus achieve savings. In the hot section of a brewhouse, in addition to trub formation, unexplained degradation reactions of iso-alpha-acids occur [2]. Experiments in this dissertation clarify that, in addition to the possible degradation reactions, there are also electrostatic interactions or rather hydrophobic interactions between the proteins and iso-alpha-acids still in solution after wort boiling, depending on the degree of oxidation of the hop bitter substances. These include proteins that are not precipitated by heat, such as protein Z, which is less altered by the brewing process than other soluble barley proteins [3]. Proteins that are already precipitated as hot trub during wort boiling and free amino acids do not react with the existing iso-alpha-acids dosed after wort boiling. The results of this dissertation define the combinatorial effects of the influencing factors on hop isomerization. Depending on the mash filtration system (wort composition) boiling times with and without hops have to be chosen to increase the isomerization rate. In addition, the non-heat precipitable proteins, which also contribute to a high quality beer foam, have been identified as the cause for the so far unexplained hop bitter acid losses after wort boiling in the brewhouse. These findings are applicable to traditional and novel brewhouse concepts. If taken into account, energy savings and a reduction in hop dosage quantities are possible. Consequently, the processing method is more economical and gentle on the raw material.

Author dc:creator

• Gänz, Nele

Advisor dc:contributor.advisor

• Drusch, Stephan

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-12784

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/14011