One of the unsolved issues I have with recipe design is how to take into account the fermentability of the wort during recipe design. How fermentable the wort is depends on, among other things, mash schedule, yeast choice, and grain bill.

Higher mash temperatures will result in more complex sugars which are not as easy for most yeasts to utilise. The use of crystal malts has a similar effect. In addition, some yeasts such as Brettanomyces are able to utilise sugars that ordinary brewers yeasts cannot, while many wine yeasts cannot metabolise maltotriose. The combination of these factors makes it quite difficult to calculate the attenuation that one might expect for a beer which deviates from the average.

This porter is a good example of just such a beer. The use of crystal malts, unmalted adjuncts and high mash temperatures means that my estimated of attenuation were off by quite a lot.

I brewed John Frum as a fairly straightforward porter, with the aim of achieving the sort of full mouthfeel that I like in my dark, wintery beers. Thanks to those efforts I expected to have produced a relatively unfermentable wort and consequently, to get quite low attenuation. I bottled after 3 weeks in the fermenter, cold crashing the beer on the balcony now that the temperatures are finally cold enough for that to be possible. At the final count I ended up with an OG of 1.018, which is an attenuation of 70% and a fair bit less than one would normally expect from Nottingham, but not unexpected considering the unfermentable wort.

Appearance

Dark, but almost completely clear, the reddish copper hues just about show through at the narrower parts of the glass. It pours with a dense tan head that hangs about quite a while and leaves a nice bit of lacing on the glass.

Smell

There is are hints of dark fruits, spice and roasty malt with an almost smoky character in the nose, but it's pretty subtle. As the beer warms up the spice becomes more noticable.

Taste

The flavour leads with sweet, caramelly malt which is followed by dried fruits and finally a palate-cleansing bitterness that just about prevents the beer tasting too sweet. The mouthfeel is slick and oily, coating the palate pleasantly and never tasting too thin. I think this is likely to be due to the rye and oats in the grain bill. Both rye and oats have a tendency to add a somewhat thick, oily character to beer thanks to the large amounts of beta-glucans they contribute to the wort. The medium carbonation is just about right here, lending some brightness to what might otherwise be a slightly heavy feeling beer.

Final Words

This has proved to be a rather popular beer with my friends, and two weeks after bottling, most of it is already gone. I will have to hoard the remaining bottles if I'm to have any chance of finding out how it ages over the next few months.

This beer is the successor to a previous porter (called Cargo Cult) that I brewed a while back. That beer turned out fairly well, but because the mouthfeel was somewhat thinner than I would have wanted, I decided to make a few changes to the recipe before brewing it again. In tweaking the recipe I ended up making enough changes that just about the only thing this beer shares with Cargo Cult is the style.

I brewed this in my shiny new brew kettle, a Bielmeier electric kettle, that I bought to replace the stove-top pot I've been using until now. Compared to my old pot this new thing is a wonder of efficiency, cutting a good hour out of my brew day just by heating up the water and wort more quickly.

I wanted plenty of malty roastiness from this beer as well as a fuller mouthfeel than I'd had with Cargo Cult. With that in mind I went with a selection of dark(ish) caramel malts as well as some flaked oats on a Marris Otter and Vienna malt base. I also used some TUOPPI Kaljamallas, which is a rye crystal malt from Laihian Mallas. It's intended for use in kotikalja, a Finnish, low-alcohol, unhopped malt beer. I figured it ought to add a fair bit of unfermentable dextrins and such, and thus contribute to a somewhat thicker tasting brew.

I mashed in high, aiming for a 67°C mash temperature. My new fancy brew kettle with its thermostat then held the temperature more or less there for 60 minutes at which point I began heating for a mash out temperature of 77C. In total I ended up with a mash time of just shy of 90 minutes. After sparging I was left with 26l of wort at 1.057.

The hopping was pretty conventional, with a bit of Magnum for a 60 minute bittering charge followed by two additions of East Kent Golding, a smaller one at 10 minutes and a larger one at flameout. I threw in 10g of Irish moss 15 minutes before the end of the boil along with the immersion chiller. I cooled the wort and siphoned it into the fermenter, giving me 21l of dark copper-coloured wort at exactly the planned OG of 1.060.

I'm fermenting this with Lallemand Nottingham which I rehydrated and pitched after aerating the wort for 20 minutes with an aquarium pump. I've never brewed with this yeast before so I'm looking forward to seeing what it will do. The fermenter went straight into the basement, which, at 18.5°C, is nice and cool compared to the flat.

Tasting Notes

Vital Details

Batch size: 21l
Expected OG: 1.060
Expected FG: 1.012
Expected ABV: 6.3%
Colour (SRM): 23.1
IBU: 30

Grist:
53.1% (3.00 kg) Marris Otter
25.6% (1.50 kg) Vienna
5.3% (0.30 kg) CaraBelge
4.4% (0.25 kg) Flaked Oats
4.4% (0.25 kg) Kaljamallas (Rye Crystal Malt)
3.5% (0.20 kg) Special B
2.7% (0.15 kg) Black Malt

Hops:
Magnum (15g / 23 IBU) @ 60 min
East Kent Golding (30g / 7 IBU) @ 10 min
East Kent Golding (70g / 0 IBU) @ flame out

Yeast:
Lallemand Nottingham