Weyermann Dunkel Uber Gravity

[emnpaul]

G'day

I think I know what the problem is but would like a second and possibly third opinion.

I have a Wayermann Dunkel I thought was ready to bottle but checked the FG for alcohol estimation purposes and came up with a FG of 1018 at 20*c. I would have predicted more like 1014.

The recipe was:
2.4kg Munich II
1.2kg Vienna
0.35Kg Caramunich II
0.07Kg Caraffa II
Yeast WLP 833 german Bock Lager
Made to 15L

Yeast pitched at 15*C then chilled to 10*C over next 6 hours.

It was fermented in my brew fridge with a Munich Helles. The temp probe was stuck to the side of the Helles which was on the top shelf and the Dunkel on the bottom of the fridge. Temp was set to 10*C.

I allowed 4 weeks ferment time before commencing crash chill and CC'ing with gelatine. Brew polyclared and alowed to sit for 3 days before taking Hydro sample. FG of 1018 has alarm bells ringing.

I admit I was lazy and a bit blaze in not taking hydro samples during fermentation and for that I am now copping my whack.

What should I do?

[warra48]

I ran your figures through BS2, and came up with an OG of 1.074 based on 75% Efficiency.
The predicted FG was 1.018.
That gives an Apparent Attenuation of around 75 to 76%. That's at the upper end of the usual range for your WLP 833 yeast.

Without knowing further details, such as your mash regime etc, I'd say you are where you should be for the yeast you used! Bock is a very malty style of beer, and Bock yeast will facilitate that. If you want higher attenuation, choose a different Lager yeast for your next batch.

[emnpaul]

Thanks for the reply Warra,

Please don't take my reply as being rude, as your response has given me cause to re-think my problem and I have checked my numbers to that end.

I ran your figures through BS2, and came up with an OG of 1.074 based on 75% Efficiency.
The predicted FG was 1.018.
That gives an Apparent Attenuation of around 75 to 76%. That's at the upper end of the usual range for your WLP 833 yeast.

I appologise for not giving more information in my original post. My OG was 1052 @18*C for 15 litres. Brewmate gives me an efficiency of 62% and an Aparent Attenuation of 66%. Pretty poor efficiency and attenuation.

Without knowing further details, such as your mash regime etc, I'd say you are where you should be for the yeast you used! Bock is a very malty style of beer, and Bock yeast will facilitate that. If you want higher attenuation, choose a different Lager yeast for your next batch

My mash regime was 55*C for 30 mins. Step to 63*C. Rest 30mins. Step to 72*C. Rest 25mins. Stir to mash out at 78*C. It was ambitious of me to dough in at 8:30pm and when I finished mash out at 10:30pm I decided it was just too late to begin sparging so left the stockpot covered with a towel overnight to resume with sparging at 7:00am. I'm not sure if sugars can congeal within the grains if left this way but I feel this could be the cause of my poor efficiency. I made a Helles the following day with a similar mash regime and got 72% efficiency and 82% attenuation using the same yeast.

Taking the above factors into consideration I have come back to my original theory that if the temperature in the top fermenter was 10*C then the one in the bottom may have been a degree or two lower and maybe just low enough to slow fermentation down to the point that it hadn't finished when I crash chilled.

I think I will try warming the brew to 12*C and rousing the yeast. If this doesn't work then I will at least end up with a slightly off style but still very drinkable Emnpaulaner Salivator dunkler bock.

[emnpaul]

Well, I warmed the brew and roused the yeast, even chucked in 100g of dissolved white sugar to get the yeasties excited. All to no avail. After the sugar had fermented out it just refused to go below SG 1.020.

I am still at a loss as to what happened with this one.

My OG reading of 1052 may be out. I took it at about 20* to the touch but I'm usually in a hurry and it may have been slightly warmer than that but I doubt it could have been out by too much. Tasted a sample at bottling and it was still pretty sweet as opposed to malty and lacked the alcohol warmth I would expect in a bock.

Another possibility is since it was brewed on my stove I may have not stirred enough between mash steps and might have de-natured some enzymes and not reached full conversion or maybe caramelised some of the sugars, putting them beyond reach of the yeast?

I pitched a cup of slurry from a Vienna lager so I doubt under pitching would be the problem.

Lack of aeration of the wort is another possibility I had considered. I have never bothered with aeration to this point, but then I always topped up my fermenter with tap water that runs through one of those aerators on the end of the tap. Now I am doing full volume boils this could be up for review if any of you think it's worth it.

Or the other, less flattering possibility. Maybe I'm just crap at AG brewing.

[warra48]

Don't talk of being crap at AG brewing, look at it as a journey on the way to enlightenment of better beer!

Aeration is more important with AG brews. You need to remember you generally boil the full volume of all your liquid for an hour minimum. That will drive off all dissolved oxygen, so you need to replace that by proper aeration.

I use an aquarium pump and an airstone, and run that several times over the first 5 or 6 hours after pitching my yeast. Each time I run it, I run it till the fermenter fills with foam, then stop.

[emnpaul]

I had heard of aerating wort but feared introducing bugs by cirulating air through it. I understood you pitched big with lagers (5 Litre starter). Is that to counteract the risk of hostile take overs from airborne bugs?

Aquarium pump is no problem for me but presumably you'd have a job specific airstone and line as opposed to grabbing it out of the fishtank for a few minutes and plonking it into your brew?

Sorry for the excess questions.

[warra48]

I only use my pump for aerating wort. It's my son-in-law who is the fish, coral, and aquarium expert! He has a great set up in their apartment.
The line I use is bought from local pet stores. It's not that expensive. They also sell cheap airstones which work quite well. However, Ross from CraftBrewer sells SS units which are more suitable.
As to introducing nasties, I filter my air through a home made filter as described in How to Brew: http://www.howtobrew.com/section1/chapter6-9-2.html
I sanitise the line and airstone. Once I finish using it I leave the air run while I retract it from my brew (this stops wort remaining in the airstone), plonk it into some sanitiser, remove it and continue to let the air run for a few minutes more to blow out any sanitiser. Then just let it air dry.
The reason for the large lager starters is the low fermentation temperature and the slower rate at which lager yeast works.

[emnpaul]

Awesome info there. Thanks Warra.

[emnpaul]

Well, I cracked one of these yesterday and after a satisfying pop upon opening, I was horrified to have it gush out all over the bench and trailing through the kitchen on the way to the sink. It seems even after all the trouble I went to, to get it to a lower gravity it has decided to "kick on" in the bottle. A "test" of some other bottles revealed it was not an isolated incident. Taste is OK and not evident of infection, that I can detect anyway.

Luckily new years is coming up and my mates and I will be able to "thoughtfully dispose" of the overcarbonated batch.