Dunkle Weizen fermentation woes

[MartinF]

After over 45 years of brewing I'm no novice, but it's interesting that there are still things that can go awry that I can't explain. So it is with a Hefe Dunkles - to give it its colloquial German name - a beer I've never brewed before despite having done regular Hefeweizen beers many times. So if anyone has any ideas, I'd be grateful...

I used Mangrove Jacks M20 yeast: a yeast I've used many times before in regular Hefeweizen bier. Fermentation stopped at 1.023 (I normally get it down to about 1.012). I warmed the FV up to 23°C. Nothing doing. I made up a starter with Safale US-05 - usually a good bet for fermenting out - and 500ml of the part-fermented wort. The starter was going like the clappers. Poured it into the FV, turned the temp controller down to 21°C and... nothing. 3 days later, after turning the temp back up to 23°C , still nothing. Not a single, further degree of gravity has fermented out after 4 more days.

The mash was a 4 step:
Mash
Acid rest — 45 °C — 10 min
Protein rest — 55 °C — 15 min
Maltose rest — 63 °C — 30 min
Saccharification rest — 72 °C — 20 min
Mash out — 75 °C — 10 min

(Ok, I know the protein rest may not have been necessary!)

Malts (5.43 kg) (for 23 litre batch)
2.8 kg (50.2%) — Weyermann Wheat Malt, Pale — Grain — 3.9 EBC
1.25 kg (22.4%) — Crisp Europils Malt — Grain — 3.4 EBC
1 kg (17.9%) — Weyermann Vienna Malt — Grain — 5.9 EBC
250 g (4.5%) — Weyermann Caraaroma — Grain — 350 EBC
130 g (2.3%) — Crisp Roast Barley — Grain — 1375 EBC

...all of which went in the mash.

Mash pH was 5.37 - as measured with my pH meter, 15mins into the mash.

Boil time was 75 mins.

Any clues? 'Cos I'm stumped.

 

[jMac]

Not sure I can help, but what was your OG? And what was your mash efficiency like with that schedule?

 

[MartinF]

Not sure I can help, but what was your OG? And what was your mash efficiency like with that schedule?

Good questions.
OG 1053
Mash efficiency...
79% in Beersmith3, 80% in Brewfather.

 

[chopps]

I have a Dunkelweizen with M20 right now that hit 1.020 after 7 days and has been VERY slowly working it’s way down. Currently 1.016 after 21 days. I’ve not seen a bubble for days but it’s still going, just really taking its time. 21C constant temp. I think maybe M20 takes its time? First time I have used it.

 

[jMac]

Another couple of questions (as I ain’t got no answers ):

1. Have you checked your hydrometer’s working?
2. Did you try a sample? Was it as sweet as 1.023 would suggest?

If there were sugars to ferment that fresh inoculation of Us-05 should have eaten right through them I’d have thought .

 

[MartinF]

I have a Dunkelweizen with M20 right now that hit 1.020 after 7 days and has been VERY slowly working it’s way down. Currently 1.016 after 21 days. I’ve not seen a bubble for days but it’s still going, just really taking its time. 21C constant temp. I think maybe M20 takes its time? First time I have used it.

I've had no problems with M20 - with regular hefeweizen - in the past. But this is my 1st Dunkles.

Interestingly, I've had stuck ferments with other dark beers (stouts & porters) when using MJ M15 (Empire Ale) and Lallemand's Windsor. Makes me doubt my methods.

 

[MartinF]

Another couple of questions (as I ain’t got no answers ):

1. Have you checked your hydrometer’s working?
2. Did you try a sample? Was it as sweet as 1.023 would suggest?

If there were sugars to ferment that fresh inoculation of Us-05 should have eaten right through them I’d have thought .

Ha!

I have a Brewbrain Float hydrometer and a very expensive (but not as expensive as the Float!!), narrow range (1.000 - 1.050) glass hydrometer. They're within 1 degree of each other.

Yes, it's sweet. Not throw-away-worthy sweet. You're right about remaining fermentable sugars, and it was fermenting well with the fresh US-05 starter. It just stopped dead after I pitched it.

I'll keg it & drink it regardless, but it's only around 3.9%ABV right now instead of the 5% it should have been.

 

[jMac]

I'll keg it & drink it regardless, but it's only around 3.9%ABV right now instead of the 5% it should have been.

Well, maybe hang on for a little bit, if you can, as @chopps suggested. I know the 05 should have already done its bit, but you never know. How many days has it been in the fermenter for in total now?

I made up a starter with Safale US-05 - usually a good bet for fermenting out - and 500ml of the part-fermented wort. The starter was going like the clappers.

This is the interesting part. The 05 was happy enough chomping through your wort in the starter jar but not when poured in the FV? There’s something weird going on there. But sorry...

 

[MartinF]

Well, maybe hang on for a little bit, if you can, as @chopps suggested. I know the 05 should have already done its bit, but you never know. How many days has it been in the fermenter for in total now?

It's 9 days now

This is the interesting part. The 05 was happy enough chomping through your wort in the starter jar but not when poured in the FV? There’s something weird going on there. But sorry...

Agreed!

 

[dad_of_jon]

I can confirm m20 finishes high but i've had 1008-1017 depending on what I was using it for. I mainly brew using extract. it will do 8%. leave the beer in fv for 3 weeks especially if the temps are the lower range it can go up to around 30c I recall.