Possibly one of my and my wife’s favourite beers from Bamberg in Mahrs aU. It’s an ungespundetes (unbunged) pale-amber Kellerbier, meaning that it was carbonated without spunding, taking up only the amount of CO2 the liquid would do under the current temperature and atmospheric pressure, and is normally served unfiltered.
Brewing ungespundetes Bier is traditional for Bamberg, and has already been described as being particular to the city’s brewing practice in the 19th century (e.g. Das Bierbrauen in allen seinen Zweigen by Johann Muntz from 1840, p.121). It also shows in the name: “aU”, which some people call the shortest beer order in the world, is local colloquialism for “ein Ungespundetes”. The Mahr brewery in Bamberg, located in the city’s district “Wunderburg” and just opposite of Keesmann brewery, has been around since 1670, and has been owned by the Michel family since 1895. They are one of the traditional Bamberg breweries, and not just because of aU, they have a faithful followership locally and around the world.
If I want to brew a clone of Mahrs aU, I first need to find out about the beer’s specifications. Fortunately, I found a video from 2010 about the production of aU that contains some information: https://www.youtube.com/watch?v=Ubmm2j-2Uq4 (embedding is unfortunatey disabled, so you’ll have to click the link to view it)
From there, we can extract quite a bit of information about the beer. It’s a bottom-fermented beer, with an original gravity of 12.7°P. The grist consists of Pilsner malt and Munich malt of unknown ratios. The sole hop variety used is Hallertauer Perle with an unknown hopping schedule or bitterness. The final beer contains about 5.2% alcohol by volume and is carbonated with 4 grams per litre of CO2.
This is already quite a bit of information that we can work with and construct a recipe out of. Of course, I don’t expect the result to be perfect, so this is just a rough first outline. Further changes to this are up to the result of the first brew.
For the grist, I will start with simply 50% Pilsner malt and 50% Munich I malt. I couldn’t find anything useful about the mashing regime employed at Mahrs, so I’m simply sticking to my preferred double decoction scheme, hopefully ending up with a wort of the right OG.
For the hops, I’m sticking to just Perle. I managed to buy fresh 2019 harvest cone hops, which in my case have 7.2% alpha acid. I estimate the bitterness of aU to be roughly around 30 IBU. This is not just based on taste testing, but also on a rough bitterness scale that Mahrs provides on their website: the Helles has 3 hops, the aU has 4 hops, and the Pils has 6 hops. The following is a lot of conjecture, but bear with me: if the Helles has roughly 20 IBU and 3 hops, then 1 hop in their proprietary scale is equivalent to 6.66 IBU. If we assume the Pils to have around 40 IBU (it is rather bitter) and 6 hops, we get the same result: 1 hop is equivlaent to 6.66 IBU. In that respect, the scale seems fairly consistent. Based on this, a beer with 4 hops bitterness should be equivalent to about 27 IBU. Now I dare anyone to correctly blind-taste the difference between 27 and 30 IBU.
So for a first test brew, I decided to simply add to hop additions, one at the beginning of the boil (90 minutes) at 1.6 g/l, and a late addition just 10 minutes before the end of the boil at 0.6 g/l. This should add the desired bitterness of about 30 IBU, and leave behind some hop flavour and aroma, without being too hop-forward.
I will ferment this beer like any of my other bottom-fermented beers at 10°C, and then briefly lager it. In the beginning, I will simply use W-34/70 yeast. I do think though that Mahrs house yeast strain has quite the impact on the overall flavour of the beer. This is noticeable in direct comparisons of their aU and their Helles which I’ve conducted, and the Helles has some underlying subtle spiciness that is very present in the aU and can’t simply be explained through the malt (the Helles most likely contains no darker malts, unlike aU) or the hops (the Helles is hopped with Hallertauer Tradition and Mittelfrüh, whereas aU is all Perle). A future point in experimentation is to see whether there is any live yeast in bottles of aU which could be grown and used to ferment later batches, or whether other commercial strains show better results, in case straight-up W-34/70 doesn’t cut it.
This is my hypothesis how an aU clone could be constructed. Whether any of speculations hold true will show when the first test brew is ready to drink. My plan is to brew it with the next few days, which means it will be ready in about 6 to 8 weeks time. I’ll keep you updated here.