Fungal Hydrophobins in the Barley-to-Beer Chain

Abstract

Fungal hydrophobins have been shown to induce gushing of beer. In order to study the occurrence and fate of hydrophobins at different stages of the production chain of beer, barley samples artificially infected in the field with Fusarium culmorum, F. graminearum and F. poae were collected during the growing period as well as during various stages of the malting process. In addition, naturally infected malt was brewed in pilot scale and samples were collected throughout the process. The samples were assayed for hydrophobin content using an ELISA method. The results showed that fungi produced hydrophobins that accumulated during barley grain development in the field, but that production was more pronounced during malting. Prolonged storage of barley tended to reduce the ability of fungi to produce hydrophobins in malting. Studies on the fate of hydrophobins during the brewing process revealed that mashing released hydrophobins from the malt into the wort. Some loss of hydrophobins occurred throughout the brewing process with spent grains, cold break (wort boiling) and surplus yeast. In addition, the beer filtration step reduced hydrophobin levels. Despite the substantial loss of hydrophobins during brewing, the level was high enough to induce the gushing detected in the final beer.

Malting and Brewing Industries Encounter Fusarium spp. Related Problems

“…By nature, they are thermostable and Műller et al [103] reported that 10% of hydrophobins go through the processes and temperatures applied during brewing process unchanged, transfer to beer and can cause gushing. A similar claim was made by Sarlin et al [79]. Kleemola et al [92] and Sarlin et al [80] demonstrated that the addition of purified fungal hydrophobins to beer causes gushing.…”

“…Fusarium species are known producers of mycotoxins, but they also excrete hyrophobins that cause gushing [35,[76][77][78][79][80][81]. Gushing can be described as uncontrolled, eruptive foaming of beer after a bottle has been opened, without previous shaking or any agitation (Figure 4).…”

“…Primary gushing is a direct result of fungal activity, mostly belonging to Fusarium sp., but it has also been linked to species of genera Aspergillus, Rhizopus, Penicillium and Nigrospora [79,88,89]. In general, gushing factors are surface-active molecules and studies point that hydrophobins, small fungal proteins characteristic for filamentous fungi, are responsible for gushing [35,79,[90][91][92][93][94][95][96][97][98].…”

“…Kleemola et al [92] and Sarlin et al [80] demonstrated that the addition of purified fungal hydrophobins to beer causes gushing. In 2007, Sarlin et al [79] found that even small concentrations of hydrophobins added to beer (only 3 µg/L) cause gushing. However, fungi used in the aforementioned studies were tagged as not relevant for gushing in Central Europe (T. reesei, F. poae and Nigrospora sp.)…”

Hydrophobins, beer foaming and gushing

“…Cox et al (2009) reported that 0.1 wt% HFBII forms exceptional stable foams across a wide range of solution pH conditions in simple solutions. However their presence in beer is undesirable because they are responsible for gushing (Sarlin et al, , 2007. Gushing is the spontaneous and wild overfoaming of overcarbonated beverages that occurs at the opening of the container without any shaking.…”