I recently attended the 35th EBC (European Brewery Convention) Congress in Porto, where I held both an oral presentation entitled ‘Newly-created hybrid lager yeast strains (S. cerevisiae x S. eubayanus) outperform both parents during brewery fermentation‘ and co-authored a poster entitled ‘Non-conventional yeast as a new tool for beer flavour modification’. I’ve already written two blog posts on our new lager yeast hybrids (see here and here), so I won’t go into details on that topic here. However, here is a link to my presentation slides in case you are interested. I more or less go over the data from our recent publication, but it should hopefully be presented in a way that is easy to follow.
The topic of our poster, i.e. the use of non-Saccharomyces yeast in brewing for increased flavour, should be a topic that is interesting for many experimental homebrewers. You can download a copy of the poster here. We did small-scale wort fermentations using 13 different non-Saccharomyces yeast species, and 3 Saccharomyces yeast species as controls. We then analyzed the concentrations of higher alcohols, esters and 4-vinylguaiacol in the resulting beers, and identified yeast species that 1) produced high amounts of esters, but 2) were also POF- (i.e. they didn’t produce 4-vinylguaiacol above the flavour threshold). This was because we were interested in applying these yeasts to beer styles where a spicy, phenolic and ‘wild’ flavour isn’t wanted. Some interesting yeasts were Kazachstania servazzi, Naumovia dairenensis, Lachancea fermentati , and Kluyveromyces marxianus.
Many of the non-Saccharomyces yeasts were quite poor at fermenting wort (with its complex mixture of sugars and with the resulting high concentrations of ethanol), so we had the idea of using them in co-fermentations together with an ale yeast strain. To maximize the flavour contribution from the non-Saccharomyces strains, yet still ensure proper attenuation from the ale strain, we first pitched only the non-Saccharomyces strain, and added the ale strain after 24 hours of fermentation. We brewed three 30 liter batches, one control with only the ale strain, one co-fermentation with Kazachstania servazzi, and one with Naumovia dairenensis. We bottled all three batches and had the beer analysed. The beers co-fermented with the wild yeasts had significantly higher level of esters than the control beer, and had a strong fruity and floral aroma.
Finally, I thought I’d do a quick summary of some topics that could be relevant for homebrewers:
- The ‘kettle hop aroma’ mystery, Praet T et al.
I missed this presentation myself, as it was parallel to the session I was having a presentation in, but I’ve seen a variation of this presentation at an earlier brewing congress. They have revealed that oxygenated sesquiterpenoids are formed during wort boiling from hop oils, and that these give the beer ‘spicy’, ‘woody’ and ‘hoppy’ notes. So these are hop aromas that require boiling, and cannot be achieved from dry hopping.
- Protein thiols and sulfite, Lund M et al.
Protein thiols and sulfite can act as antioxidants, and their presence in beer can improve beer flavour stability. They noticed that the concentrations of these in wort can be increased by supplementing proteases to the mash. Protease supplementation also increased the flavour stability of the resulting beers. Perhaps flavour stability can be improved by optimising the mashing conditions (e.g. utilizing the proteases already found in the malt)?
- Genetic metabolism of hop terpenoids by yeast in beer, Tristam P et al.
I missed this presentation myself, so am going only by comments from my colleague and the abstract. Apparently they have looked at how various hop essential oil compounds are metabolised by the yeast during fermentation. They found that the ATF1 gene is required for the biotransformation of linalool and geraniol to their acetate esters, and the OYE2 gene is required for the biotransformation of geraniol to citronellol. This means that different yeast strains (depending on their genetic background and the activity of the corresponding enzymes) may produce beers with different hop aroma profiles!
- Influence of dry hopping on changes in the key aroma compounds of pale lager beer, Stingl S et al.
They had studied how various hop compounds are transferred to the beer during dry hopping, and looked at how the ratio of linalool to myrcene in the beer affects the aroma. Apparently the transfer of linalool to beer is very rapid during dry hopping, with maximum concentrations reached within an hour. Myrcene transfer is much slower, and it takes several days to reach the maximum concentration. At high concentrations, myrcene is thought to have an unpleasant aroma, so a short dry hop time (e.g. 1-4 days) might actually be preferable.
- A high throughput monitoring of phenotypic changes in Brewer’s yeast during serial repitching, Kocar N et al.
They had done some studies on what physiological, genetic and proteomic changes occur during serial repitching. They did 16 repitching cycles at industry-scale and 31 repitching cycles at laboratory-scale, and it seems like you can repitch around 15 times without any big changes in physiology, karyotype or proteome. So don’t be scared to reuse your yeast a couple of times (this requires good sanitation practices of course)!
- Beyond iso-alpha acids, Shellhammer T et al.
They studied how oxidized hop acids and hop polyphenols affect the IBU value and beer bitterness. They notices that oxidized alpha acids, i.e. humulinones, that transfer from the hops to the beer while dry hopping, not only affects the IBU value of the beer but also the perceived bitterness. They are perceived as less bitter that iso-alpha acids though. Some commercial heavily dry-hopped beers even had higher bitterness contribution from the humulinones than the iso-alpha acids. So dry hopping does increase bitterness!
- Bitterness impact of common brewing spices, O’Neill C et al.
They studied how various common brewing spices affected the measured and perceived bitterness. Especially cinnamon seems to increase IBU and perceived bitterness. Coffee beans and coriander also seem to increase the perceived bitterness. So keep that in mind when adding spices to your beer!
- Aroma contributions from Simcoe and Hallertau Mittelfrüh hops to beer using different hopping regimes, Sharp D et al.
They had looked at and compared how different hopping regimes (kettle hopping, whirlpool hopping and dry hopping) and two hop cultivars (Simcoe and Hallertau Mittelfrüh) affect the perceived aroma and concentration of various hop oil compounds in the beer. For a homebrewer, it was no surprise that Simcoe gave more tones of tropical fruit, citrus, stone fruit and pine compared to HM. Dry hopping and whirlpool hopping seem to give similar effects, which is something to keep in mind when planning your hop schedule.
There were probably many more interesting presentations (and I decided to leave out the posters from here as well), but unfortunately I wasn’t able to see them all due to the triple parallel sessions during the conference. All in all it was a very interesting conference with lots of interesting researchers and research topics! Already looking forward to the next one! Please leave a comment if you have any questions, and I can try to answer them as best as I can.
