Yearly Archives: 2015

Physicochemical analysis of Sahti

Last summer, me and a couple of colleagues visited the 23rd National Championship in Sahti brewing, which was organized in northern Espoo. The purpose of our visit was not to compete or just drink Sahti, but rather we were there to collect samples for a research project: we had decided it was time that a thorough physical and chemical analysis on Sahti was to be performed.

First of all, what is Sahti? Well, Sahti is a traditional farmhouse beer that has been produced and consumed in Finland for centuries. The Sahti beers that I have tried have all been sweet and alcoholic, with strong yeast tones in the flavour. The aroma of isoamyl acetate (banana) has particularly stood out. If you are interested in a more thorough introduction, then you can head over to this blog. For instructions (in Finnish) on how to make your own Sahti at home, you can check out this blog.


© Nesster / Flickr

We collected samples from 12 random Sahti at the Championships (all from different parts of the country). We then did some thorough analysis on these samples, including: ABV%, residual extract, IBU, colour, foam stability, sugar profile, organic acid profile, higher alcohol profile, ester profile, phenolic acid profile, 4-vinylguaiacol content, and finally we looked for juniper-derived components with GC/MS. We also analyzed seven commercial beers as references (one Sahti, two Pale Lagers, two Hefeweizen, and two Porters).

There was quite a lot of variation between the samples, but in general the Sahti had quite high ABV%, residual extract and ester concentrations, as was expected. The isoamyl acetate (banana aroma) concentration was really high in some of the Sahti (up to around 14.5 mg/L). Since Sahti is unhopped or lightly hopped, the bitterness values were low. Also, since Sahti is typically uncarbonated or lowly carbonated, the samples had really poor foam stability. All samples also had 4-vinylguaiacol (clove-like aroma, typically found in Hefeweizens and Belgian-style ales) concentrations above the flavour threshold. This is a presumably a result of the use of Finnish baker’s yeast. It can be concluded that Sahti indeed is a unique beer style, with some very interesting properties. I’m not that big of a fan myself, but I can understand the fascination behind the style.

You can download a pre-print version (i.e. it hasn’t been formatted yet) of the publication here.


Sahti, a strong, unhopped farmhouse beer flavoured with juniper is still actively brewed in rural areas in Finland. Presented here is the first comprehensive analysis of the physical and chemical properties of this unique beer style. Twelve sahti samples from the southwest of Finland were analysed and while properties varied, the beers generally had high levels of alcohol (mean = 7.9% ABV) and high residual extract (mean = 9.5 °P). Foam stability was negligible, as is typical for the style, and glycerol concentrations at 3.1 – 4.7 g/l were higher than in reference beers (commercial lager, wheat beer and porter). Both of these features may be attributed to the very high gravity conditions employed in brewing sahti beers. Bitterness levels were relatively low (3 – 13 IBU) due to the absence or moderate use of hops. All samples contained detectable levels of the clove-like compound 4-vinylguaiacol due to the use of baker’s rather than brewer’s yeast for brewing. Concentrations of higher alcohols and esters were high, with many individual aroma compounds being above the normal flavour thresholds. Results have highlighted the uniqueness of this style of beer in comparison to commercially available beers and have contributed to our understanding of the reasons for the particular sensorial properties of this traditional beer style.

Homebrew: Wedding Hybrid – American Pale ‘Lager’

Today it was time to brew the third batch of beer for my wedding in August (see my previous posts for the Wedding Pils and Wedding Blond): an American Pale Ale-like beer, fermented with one of my newly created A62×C902 lager yeast hybrids. I’m not really sure what to expect from the beer, but I’m hoping for a really fruity aroma and flavour. Apart from the large amount of experimental fermentations we’ve done with the yeast hybrids at work, we have also fermented a bigger batch of ‘typical’ lager wort with one of the hybrids, which we then kegged and taste-tested. That beer at least had a really fruity flavour, with plenty of ethyl esters and isoamyl acetate. That wort was relatively lightly hopped, so it will be really interesting to see how the yeast aromas go along with a more heavily hopped beer. I’m hoping for bold flavours, yet still an easy-to-drink beer.

The recipe might seem a bit complicated, as it features six different malts and five hop varieties. This is because I’m using up some opened malt and hop bags. I’m hoping that the ingredients come together nicely, and that the flavours aren’t too muddled in the final beer. The malt bill consists mainly of some Pilsner and Maris Otter malt as base, with a hefty portion of Munich malt to lend some more breadiness. The rest of the malt bill consists of some CaraPils, oat flakes and Crystal 6oL, in order to give the beer some increased mouthfeel and a hint of caramel. I aimed for an original gravity of around 1.050, in order to get a beer with around 5% ABV. For the hops, I chose to bitter with some leftover Styrian Goldings and Simcoe, and at flameout I added a mixture of Amarillo, Citra, Saphir and Simcoe. I aimed to keep the bitterness levels quite low and instead concentrate on a massive hop flavor and aroma. I pitched a 2.5L starter of one of my lager yeast hybrids after I had cooled the wort down to around 17C. I kegged the Pilsner yesterday (it was tasting awesome by the way!), so my fermentation fridge was free again. I set the fermentation temperature to 15C, and 6 hours after pitching there was already slight activity in the airlock. Fingers crossed that this turns into an awesome beer!

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Report from the 35th European Brewing Convention Congress

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.

Homebrew: Wedding Blond – Belgian Blond

I just came back from the 35th EBC Congress in Porto, where there were some really interesting presentations and posters. I’m currently writing up a post with a summary of the topics that are relevant to homebrewers, and I should hopefully have it ready during next week! Today I also brewed the second batch of beer for my wedding in August (see my previous post for the Wedding Pils): a Belgian Blond based on a recipe I brewed almost three years ago. The beer I brewed then was light, hoppy and featured some nice esters and phenolics from the yeast in the aroma. Should be perfect for a warm summer day, perhaps together with the seafood on the menu.

The recipe is quite simple, featuring a malt bill of mainly Pilsner malt, with just hints of flaked oats and cane sugar, to contribute some more mouthfeel and dry out the beer. I aimed for an original gravity of around 1.050, in order to get a beer with around 5.5% ABV. For the hops, I again used Herkules for bittering, but instead added some Styrian Goldings and Saphir towards the end of the boil. I pitched a 1L starter of WLP530 (Abbey Ale) after I had cooled the wort down to around 20C. My fermentation fridge is still occupied by the Pilsner, so chose to ferment this at room temperature. This should help bring out some yeast tones in the aroma as well. I placed the fermenter in a slightly colder room (~ 18C), but I imagine the wort temperature will rise to about 23C during active fermentation. I checked the fermenter 5 hours after pitching and there was already rapid bubbling in the airlock meaning that the yeast was already chewing through the sugars. Another smooth brewday!

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Homebrew: Wedding Pils – German Pilsner

I’m getting married in August, and of course I’ve planned to brew a range of beers for the wedding. I already have a big Imperial Stout ready, and it will probably be served together with dessert. It has been keg-aging for over a year, and it was tasting really nice a couple of weeks ago when I had a small sample. Yesterday I brewed the first batch of the ‘lighter’ beers: a German Pilsner. I’m also planning to make a Belgian Blond, American Pale Ale, American IPA, and a beer brewed with one of my recently developed hybrid lager yeasts.

I haven’t brewed for a while, since we are still renovating our brewing space, but everything went surprisingly smoothly: I was done in 5 hours and managed to hit all the numbers. I aimed for a hoppy and crisp Pilsner, in the style of Firestone Walker’s amazing Pivo Pils. The malt bill consisted of Pilsner malt and a hint of Cara-pils, and the original gravity was 1.048. For hops, I used Herkules at 90 minutes and Spalter at 30 minutes and flame-out (total IBU around 40-45). I will be dry-hopping with a slight amount of Saphir after the fermentation has slowed down. I’m fermenting with Fermentis’ W34/70, since I didn’t feel like making a huge yeast starter. I’ve had good success with it in the past, so it shouldn’t be a problem. I’m starting at 10C, but will be raising the fermentation temperature to 12C after a couple of days of fermentation. Hopefully everything goes well, and the wedding guests will be able to enjoy a clean, dry and crisp pilsner on a warm and beautiful August day!

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Small update

Sorry again for the inactivity. Not much interesting has happened on the homebrew front. We’ve made slight progress with our homebrewery renovation, as we’ve put up some 160mm ventilation pipes and installed an inline exhaust fan in order to transfer the steam generated from the boil outside. The fan seems really powerful, which is a good sign, but we still need to test it by boiling some water in our boil kettle. We will most likely need to adjust the vent hood, so that it is closer to the top of the kettle. We’ve also started drawing cables for the electrics, and pipes for the water will be next. After that we have some thorough cleaning to do and painting the walls. We hope to be able to brew our first batch in the new homebrewery in May. Can’t wait!





At work I have lots of interesting new results as well, which I hopefully will be able to post about later during the year. I’m also looking into generating some new S. cerevisiae × S. cerevisiae intraspecific hybrids for homebrew use. A combination of WLP001 and WLP002 sounds good doesn’t it? Or a hybrid of Conan and WLP644 for a really fruity IPA? Anyways, the possibilities are endless (in theory at least).

Brewing at J’s homebrewery

On Sunday I had the chance to brew beer together with my colleague J at his homebrewery. He has some really cool ‘homemade’ equipment, which allows him to brew up to approximately 140-liter batches of beer. He has been brewing mostly Sahti (which you will notice from the equipment as well), but on Sunday we decided to brew an easy-to-drink Pale Ale hopped with Cascade. We aimed for an ABV around 5% and an IBU of around 35, in order to appeal to as large of an audience as possible (J is planning to serve it at a friend’s party). The malt bill consisted of mainly pale ale malt, together with a small amount of munich malt (to give some strength to the malt backbone) and crystal 10 (to lend some body and a slight hint of caramel). The hop schedule should give the beer plenty of grapefruit and floral tones in the aroma and flavour. We are fermenting with J’s ‘house’ (or shall we say favourite) yeast strain, WLP007, to lend a dry and clear beer, with slight hints of fruity esters. The batch size was 100 liters, so approximately 2.5-5 times bigger than my usual batches. The brewday went really well and we hit most of targets. Hopefully the beer will taste good as well! Thanks J for the opportunity to come and brew with you! Below you will find some pictures I took during the day.

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We began the brewday by crushing the malt, which J had pre-weighed prior to my arrival. He uses a mill that looks quite similar to my Monster Mill MM-2. Crushing 20 kg of malt took about 10 minutes with a cordless drill.

While we were crushing, the mashing water was being pre-heated in the 200-liter brewing kettle. J has modified a 200-liter tiltable kettle (normally used in professional kitchens) with a PID controller, which allows him to precisely control the mash temperature. The kettle is powered by a steam jacket, which allows for rapid and even heating along the whole surface of the kettle (no problems with scorching here). He has mounted a motor-powered mash paddle in the middle of the lid (which was continuously mixing the mash), together with a long thermowell containing the temperature sensor. A really cool set-up! Hopefully will be able to have something similar at some point.



Below is the lautering vessel, which is of the kuurna-type, i.e. one that is traditional used for making sahti. When making Sahti, the vessel can be filled with juniper twigs to help with lautering and to lend some flavour. We instead used sheets of perforated stainless steel to act as a false bottom and uphold the malt bed.


After the 90-minute mash, we transferred the whole content of the kettle into the lautering vessel. We used smaller buckets for the transfer, which took a couple of minutes. The engineer in me would probably want a more automated and less laborious solution, but J was happy with this set-up. When the kettle was empty, it was quickly rinsed with water, after which the sparge water was heated. In the meanwhile we were circulating the wort in order to clear it up. No fear of hot-side oxidation here, with plenty of splashing. I would again probably take an easier way out, with a valve in the end and a pump to recirculate the wort.


Here is a picture of the control panel as we are heating the sparge water up to the target temperature of 75C. It took maybe 10 minutes to heat the 70 liters of sparge water the remaining 30 degrees up to 75C.


Here is a picture of the exhaust system. He uses the same exhaust fan for leading away welding fumes, so it serves several purposes. It was very effective in removing the steam produced during the boil (which you will see a couple of pictures down).


We collected the pre-boil wort in the kettle. We ended up with around 120 liters of wort, with a pre-boil gravity of around 1.042 (so slightly higher efficiency than expected).


After the boil had started, we opened up the hole in the lid, added in the bittering hops, and put on the exhaust fan. As you can see, the fumes are collected nicely into the ventilation tubes.


Here are 150 g of Cascade pellets which are to be added with 15 minutes left in the boil. The remaining 250 g of flame-out hops are still waiting in the black bag.


Below is 175 ml of WLP007 yeast slurry which is to be pitched into the wort after cooling. Slightly on the low side for this big of a batch, but luckily the beer is quite low-gravity.


Here we are cooling through a plate chiller. No pump is used to transfer the wort, only gravity (the kettle is tilted so the valve is lowered below the liquid). Emptying of the kettle took about 15-20 minutes. Before cooling we whirlpooled the hot wort for around 15 minutes, to collect any solid matter at the bottom. The whirlpool was initiated with the same motor-driven mash peddle which stirred the mash.


Here is a picture of the whirlpool cake. Quite a lot of hop debris and trub!


We ended up with around 100 liters of 1.048 wort. This will hopefully become a really refreshing and sessionable Pale Ale for warm spring days!


Thanks again J!

How new yeast species are inspiring a revolution in brewing

Note, this is a repost of an article I wrote for VTT’s Industrial Biotechnology Blog.

Lager beers – sometimes crisp & light pilsners, sometimes dark & malty doppelbocks, have a common denominator: They are all produced using the lager yeast Saccharomyces pastorianus, the workhorse of the lager brewing industry. This yeast is known for its tolerance to lower temperatures, and brewers take advantage of this when producing lager beers.

These beers typically have a ‘clean’ flavour profile (i.e. lack of yeast character) you see, and by fermenting the beer at colder temperatures, the yeast produces less flavour-active by-products.


Recent analysis of lager brewing yeast genomes has revealed that the many hundreds of strains used in the brewing industry are, in fact, all closely related – more like multiple variants of the same strain than individual strains. Brewers have essentially been using the same strain to brew lager beers for probably 500 years. This is in stark contrast to the other fermented beverage industries, ale, whiskey, wine, cider and so on, where a rich and diverse collection of individual yeast strains is taken for granted.

Therefore, there is huge potential for introducing diversity into the lager brewing industry by generating new strains of lager yeast.

But before one can create new lager yeast it is important to understand what exactly the lager yeast is…

It has been known for some time that lager yeast is actually a hybrid species – more like a mule than the proverbial workhorse. It was clear that one parent was the well-known ale yeast Saccharomyces cerevisiae. It wasn’t until recently that the other side of the family, Saccharomyces eubayanus, was discovered. This discovery has allowed for the improved characterization of lager yeasts, and also opened up the possibility to create new tailor-made lager yeast strains. This is possible through mating of selected strains from the two parent species. These new strains could, e.g. produce unique flavours or ferment the beer more efficiently.

This is exactly what has been the focus of our ongoing research projects at VTT.


The research team. From left to right: Brian Gibson, Kristoffer Krogerus, Virve Vidgren and Frederico Magalhães in VTT’s pilot brewery.

Screening perfect parents to mate

There are four main challenges in generating new lager yeasts: To select suitable parent strains. To get the parents to mate. To separate the hybrid cells from the parents. And finally, to confirm that they actually are hybrids.

We began by screening a range of ale yeast strains, from both VTT’s Culture Collection and commercial yeast suppliers, for beneficial fermentation properties. Once suitable parent ale yeast strains had been identified, the next step was to try to mate them with a strain of S. eubayanus, the other parent of lager yeast.

Before mating, the parent strains still had to be modified with selection markers, so that any hybrid cells could be isolated from the population. We did this by selecting spontaneous auxotrophic mutants of the parent strains, i.e. cells that weren’t able to grow on media lacking certain amino acids. This meant the hybrid cells could be selected by their ability to grow on media lacking these certain amino acids. Mating was then attempted by simply mixing populations of both parent strains, and letting them grow for a couple of days.

Seub_cells© VTT/Ulla Holopainen

After isolating some potential hybrid cells, their hybrid status was confirmed through various PCR tests, which showed whether DNA from both parent strains was present in them. After confirmation that we had produced our own lager yeast hybrids, we wanted to compare them to the parent strains in an actual wort fermentation.

To our pleasant surprise, all hybrid strains performed better than both parent strains, fermenting faster and reaching higher ethanol contents!

The hybrid strains also inherited beneficial properties from both parent strains, such as strong flocculation, cold tolerance and maltotriose utilization.

These first results suggest that this technique is suitable for producing new lager yeast strains with unique properties. These new strains also have the benefit of being non-GMO, which currently at least remains a necessity for brewers.

We are continuing our attempts to find and create perfect lager yeast hybrids at VTT. Our research will especially pay attention to flavour formation and determining how their genetic composition is reflected in their physiology.

Our work will show, for the first time, that such hybrids can be created and how they can be applied in the brewing industry. The results will appear shortly in the Journal of Industrial Microbiology and Biotechology:

Krogerus, K., Magalhães, F., Vidgren, V. & Gibson, B. (2015) New lager yeast strains generated by interspecific hybridization. Journal of Industrial Microbiology and Biotechnology, in press. DOI:10.1007/s10295-015-1597-6.

Maybe someday also you have an opportunity to enjoy these new tasty lager beers in your local pub. Cheers!

Tasting Impressions: Sim/arillo IPA

The ‘single malt’ IPA, hopped with Simcoe and Amarillo, that we brewed slightly over a month ago, has now been in the keg for around three weeks. This means it’s time to write up some tasting notes of the beer, while its still at its prime. Quite a lot of trub ended up in the fermenter as we transferred from the boil kettle, and it seems to have had a positive effect on the clarity of the beer. It was crystal-clear when transferred to the keg, despite using US-05 and no cold crash, and only had the slightest chill haze when served. It looks cloudier in the picture below, because of condensation on the outside of the glass. Anyways, to the tasting notes!


The beer pours with a golden color with slight hints of orange. It is surprisingly dark for a malt bill of only Maris Otter. As mentioned, there is a slight amount of chill haze, that disappears as the beer warms up in the glass. A white, oily foam head is formed during the pour, and it collapses slowly leaving drapes of lacing along the glass. A really nice, and very typical, appearance for an IPA.

The beer is really exploding with hop aroma, and it just jumps to your face out of the glass as you close in. There are tones of citrus (specifically grapefruit), pineapple, pine resin and floral perfume. A really nice and fresh hop aroma, that is really hard to find from commercial beers (at least here in Finland, when the time from bottling to serving can be several months). Not much other hops in the aroma, which is the way I like it for IPAs.

The flavor is mostly hop-dominated as well, with very little presence of any malt or yeast tones. The flavor begins with hints of biscuits and malts, but these are instantaneously overtaken by a resiny hoppiness. While the aroma was very fruity, the flavor draws more towards the resiny, piney, earthy and grassy part of the spectrum. There are slight tones of grapefruit in the background as well, but these are more subtle than what could be found in the aroma. The flavor finishes dry and with a hefty bitterness that suits the style. The mouthfeel is dry and light, and the carbonation level is medium-low, which I think suits the beer well. A typical West Coast IPA, with a flavor that is solely focused on the hops and that finishes dry and bitter. Even though the aroma was amazingly fruity, I wish the beer had slightly more of those tones in the flavor as well. Otherwise a really nice homebrew!

Generating new lager yeast hybrids

For my PhD thesis, I’ve been researching the flavour- and stress-related properties of brewing yeast hybrids. It has been known for some time that lager yeast (Saccharomyces pastorianus) is actually a hybrid species, and that one parent was the well-known ale yeast Saccharomyces cerevisiae. In 2011, the other side of the family, Saccharomyces eubayanus, was discovered. This discovery has allowed for the improved characterization of lager yeasts, and also opened up the possibility to create new tailor-made lager yeast strains. This is possible through mating of selected strains from the two parent species.

graphical abstractThis is exactly what I’ve been doing during the past year, and I’m happy to announce that we recently published our first results (New lager yeast strains generated by interspecific hybridization) in the Journal of Industrial Microbiology and Biotechnology. We mated a strongly flocculent production ale strain (from a brewery in the UK) with S. eubayanus, to produce lager yeast hybrids which performed better than the parent strains, and inherited beneficial properties from both. This will open up the possibility to produce a range of new lager yeast strains, with e.g. interesting flavour production and increased stress tolerance. We already have plenty of new interesting hybrid combinations that I’m looking forward to characterizing. I will post more details in a later post, but in the meanwhile feel free to read the publication if you are interested, it is Open Access!

Link to the publication:


The interspecific hybrid Saccharomyces pastorianus is the most commonly used yeast in brewery fermentations worldwide. Here, we generated de novo lager yeast hybrids by mating a domesticated and strongly flocculent Saccharomyces cerevisiae ale strain with the Saccharomyces eubayanus type strain. The hybrids were characterized with respect to the parent strains in a wort fermentation performed at temperatures typical for lager brewing (12 °C). The resulting beers were analysed for sugar and aroma compounds, while the yeasts were tested for their flocculation ability and α-glucoside transport capability. These hybrids inherited beneficial properties from both parent strains (cryotolerance, maltotriose utilization and strong flocculation) and showed apparent hybrid vigour, fermenting faster and producing beer with higher alcohol content (5.6 vs 4.5 % ABV) than the parents. Results suggest that interspecific hybridization is suitable for production of novel non-GM lager yeast strains with unique properties and will help in elucidating the evolutionary history of industrial lager yeast.