Czech Yourself Before You Wreck Yourself — Lager Brew Day

This weekend I decided to brew my lager recipe that I’ve had kicking about for a long time. It’s freezing cold here in the UK at the minute so what better time to brew something that requires cold fermentation?

I was also trying out the new Grainfather connect control box and app for my first full brew day at home with the new equipment (full disclosure, I work in marketing for Grainfather) so I was quite excited as it’s always fun to brew with new toys.

My lager recipe is really simple;

Pilsner grain bill

OG: 1.043 FG: 1.011 SRM: 2.1 IBU: 30.8 BU/GU: 0.72 ABV: 4.1%


4kg Bohemian Pilsner (95%)

0.2kg Acidulated malt (5%)


15g Hallertau Blank @ 90 minutes (17.6 IBU’s)

40g Saaz @ 90 minutes (11.6 IBU’s)

10g Saaz @ 10 minutes (1.6 IBU’s)


2 x Mangrove Jacks M84 Bohemian Lager yeast

Pilsner malt is obviously traditional in a Pilsner and pretty vital in getting that crisp flavour with little in the way of maltiness. I like to use a small percentage of acidulated (around 5%) to help with the mash pH.

Saaz hops are also traditional in a Czech pilsner but I had some hallertau blank which I added to the bittering charge. The aroma of these hops is described as grapefruit, pineapple, grape and lemongrass so although delicious, not really to style in this beer.

Hallertau Blank for bittering but not a good aroma choice for a traditional Pilsner

I decided that I was going to have a few mash steps in the process — firstly because I wanted to test the new controller but also because I wanted to target both alpha and beta amylase in the mash.

Alpha amylase can work on the ‘joints’ of complex sugar molecules, creating long branches which results in a less fermentable wort and more body in your final beer and is most active between 68C — 75C. Beta amylase on the other hand works on the end of branches, creating smaller chains and therefore a more fermentable wort and a thinner body and is most active between 54–65C. By targeting both enzymes in the same mash I was hoping to create a highly fermentable wort which would lead to a crsip and dry final beer.

I brewed at 62C for 40 minutes before ramping up to 69C for 60 minutes and finally 75C for 10 minutes for a mash out. I had imported this recipe as a .xml file to the Grainfather app so when I connected to the controller it automatically ramped through the temperatures at the given times which was very handy!

Pre-boil I had a gravity of 1.044 which seems wrong as I was only using 4.2kgs of grain

Refractometer reading of ~1.044

I boiled for 90 minutes which is pretty standard for a lager recipe. Pilsner has a large amount of the precursor to DMS present (S-methylmethionine) which is produced during germination of the barley. DMS is that corn flavour and aroma that is typically seen as an off flavour in most lagers (although small amounts are acceptable in some cases). By boiling uncovered for a long period of time you should drive off DMS, preventing it from occurring in your finished beer.

I chilled the beer quickly down to 14C before pitching two packs of m84 bohemian lager yeast.

I ended up with ~18 litres in the fermenter and a gravity of 1.058 which is an efficiency of 81.5% so much higher than my predicted and usual 75% efficiency. Possibly a result of the longer mash? I’d planned for a 23 litre batch though so at 23 litres I would have gotten 1.045 at the same efficiency — not far off my 1.043 prediction.

hydrometer reading

So overall a successful brewday. I was really happy with the way the new controller performed. The temperature control has made a huge difference to my brewing and being able to monitor things on your tablet or phone just makes things so easy.

There’s a long fermentation time on this now. I don’t have a brew fridge so I’m going for a very risky method of leaving the fermenter in the garage and hoping for the best. I’ll wait until I reach a little above my target final gravity (1.011) before moving the fermenter indoors to perform a diacetyl rest for two to three days.

Diacetyl is a flavour compound produced naturally by yeast during fermentation which will usually be cleaned up by the yeast towards the end of fermentation. This clean up occurs slower at colder temperatures though so when producing a cold fermented lager it is important to utilise a diacetyl rest to assist in the cleaning up of this by-product which tastes like butterscotch in your finished beer.

After the diacetyl rest it’s back outside for the fermenter for an extended period of lagering. This can be up to six months traditionally but I’m not that patient and I’m a bit nervous of trying to re-yeast the beer if I leave it that long.

Re-yeasting refers to the process of adding a small amount of yeast back into your beer at bottling time in order to help with bottle conditioning. It is useful in beers like lagers where they have gone through extended periods of cold storage and there is not enough viable yeast left to condition the beer in the bottle. Some brewers suggest this is not required.

So it will be a long wait on this one before I get to try it but I’ll make sure I come back and do the tasting notes. In the meantime I wanted to share my process on the day!

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