Lager yeast trial and decoction conundrum

Homebrew lager yeast

This trial was something close to my heart, my desert island beer is Emersons Pilsner, a classic beer from New Zealand that’s in the Pilsner style but uses New Zealand hops specifically Riwaka. The original task I had was to test two different yeast strains, the classic W34/70 and the San Francisco steam beer strain.

W34/70 is the most widely used lager strain in the world, it’s a classic German strain and enjoys traditional lager fermentation treatment a long slow fermentation at cool temperatures.

San Francisco steam beer by contrast is very niche, it’s a very interesting strain, it’s a lager strain but rather than fermenting at cool temperatures it ferments at 18 degrees Celsius without the off flavours exhibited by a lager yeast fermented at the same temperature.

So with this in mind I decided to create a beer that I would enjoy, to add to this I always enjoy testing myself and in my opinion lager brewing is a testing art especially when using old techniques. My admiration for NZ pilsners is only surpassed by my admiration for the brewing skill that German brewers have so in a nod to them I decided to double decoct my pilsner and use biological acidification of the mash for pH adjustment.

Malt bill:

95% Pilsner malt, 5% Acidulated malt (calculated for a pH of 5.2)

Mash schedule:

Homebrew Mash In

– Mash in 500C for 35 mins

– Decoct part of the mash and heat to 650C for 15 mins then continue heating to boil for 15mins

– Add back to main mash which raises the temperature to 640C and hold for 20mins

– Decoct part of the mash and boil for 15mins

– Add back to the main mash raising the temperature to 680C and hold for 20 mins

– Heat to 750C and hold for 10 mins

– Mash complete, runoff in the normal manner and boil for 90mins

– I first wort hopped with Waimea and end of the boil hopped at 5.2g/L with Motueka, Nelson Sauvin and Waimea.

W34/70 was fermented at 100C, Steam beer was fermented at 180C


I was really pleased with both beers, the consensus of the tasting panel concluded that the pilsner brewed with Steam beer yeast was a superior pilsner because it was cleaner and more crisp displaying more pilsner like characteristics.

I found this to be very interesting considering I preferred the W34/70 version, upon review it was obvious that the reason I preferred the W34/70 version was because with the elevated sulphur profile it tasted and smelt more like NZ pilsners that I’m used to drinking.

Decoction conundrum:Lager Yeast Homebrew

As part of the trial I was determined to answer the age old question…are decoction mashes worth the hassle, do they in fact impart positive characteristics to the finished beer?

Yes I know, there’s no need to decoct malt anymore it’s much better modified….that doesn’t answer my question though, why do so many German breweries still do it if there’s no need?

To answer this question I brewed the same beer the next day, same ingredients, same yeast but no decoction.


In a blind triangle tasting the results were interesting, 100% of the tasters picked the decocted versions from the non-decocted versions. When asked which they preferred and why, all tasters preferred the decocted versions because the beer had more body and better malt character.

These Germans are on to something……

Comment below with your favourite yeast for brewing lagers and why.

Formerly of Fullers, Thornbridge and Buxton. Now a freelance Black IPA advocate, homebrew geezer and creator of Baby Back Bacon Black IPA™


  • Reply October 18, 2014

    Lance Blackman

    I have still yet to brew a lager and I am edging ever closer to it, recently visited the Czech Republic and noted the triple decoction method with great interest and really want to have a go. Reading your article has only reaffirmed this! However I think I will still nod towards a traditional Czech Pilsner with Saaz but the idea of using different BIPA interest me! Cheers! I’ll be back to let you know how it goes!

  • Reply November 29, 2014

    Lee Walker

    I’ve always been aware of the benefits of deccoction mashing so the results of this test are unsirprising. I think the real test though is deccoction vs melanoidin malt. I’ve since read that deccoction isn’t worth the effort, not because of well modified malt but because melanoidin malt can be used instead.

  • Reply December 2, 2014


    Hi Lee,

    This is a common misconception, while melanoidin malt mimics some of the character delivered to the beer from a decoction regime it does not deliver all the character peculiar to it.

    When decocting the mash the starch is gelated and husk compounds are extracted, ordinarily, this would be a cause for concern but when decocting the pH should be low and the thickest part of the mash used creating a low level of polyphenol extraction. This low level polyphenol extraction is part of the decoction character and cannot be mimicked by using melanoidin malt.


Leave a Reply