Under attenuation problems

[Scott Lyon]

Hi Folks,

Recently I have been having some problems with under attenuation of my beers, I have moved to a new area and restarted brewing after a gap of 6 months or so. I have a Dunkelweizen in the fermenter at the mo, made 1 litre starter (1.035 OG) with a vile of WLP300 24 hours before pitching into 1.052 wort (24 litres) fermented at 17C as per brewing classic styles. The vile was fairly fresh with the beersmith pitching calculator saying that it should be 77% viable. It started up within 12 hours and was going well, after 3 days took a reading of 1.035, all good, then after another 3 days noticed activity had stopped, took a reading and it is only 1.030. I think I have done everything right, both the wort and starter had nutrients, bubbled air thru the wort with a fish tank pump for 30 mins before pitching. Mashed @ 66C and was prob at around 64.5 buy the end of 90 min. so the wort should be pretty fermentable. The last two brews before this one also hung up toward the end too, they were not temp. controlled and I expected the new controller to fix the problem. Generally when I do a 38-40 litre brew I pitch 2 packets of dry US-05 so I don't think I'm under pitching.

So to sum up, I have got:

Enough nutrients (1 tsp/24 L )

Enough O2 (30 min of air bubbled thru)

Temp of 17C (+/- less that 1C)

Pretty careful with hygiene 

A fermentable wort mashed @ 66 and only 1.052 OG

So I'm a bit stumped.

Anyone have any ideas or suggestions?

Cheers

Scottie

[Matt Smith]

Have you checked if your thermometer is reading accurately? I had over attenuation issues a while back, checked my thermometer and it was reading about 2 degrees too high, so my 68 degree mashes were actually 66. You may have the opposite problem?

[Peter Smith]

try repitching 2nd gen us05 , I think it gets better with generations...

also aeration?

[Des Ross]

Given that there was a healthy 1L starter, oxygen at pitching and that you obviously have a fermentation, I would be patient. I doubt you need more yeast and introducing more oxygen after more than 24 hours fermentation can cause oxidation issues. Raising the fermentation temperature up to 20C may help. Perhaps in future brews, give more attention to more oxygenation when you pitch the yeast...I dont infuse oxygen but pour the cooled wort (together with the yeast) into the fermenter from a good height' followed by vigorous stirring/ whisking for at least another minute....never had an issue with a slow or stuck ferment.

[Scott Lyon]

Hi Matt, Not sure if you have followed this thread but it turns out that you were on the mark. Spent  the morning trying to make sense of the four different thermometers I own, turns out that my two glass thermometers read different at different temps. White one reads 64.5 at 65C and the yellow one I use for mashing reads 63 at 65C, However at 100C (boiling water) white reads 104, and yellow 99, I ended up calibrating my digital temp controller to 100C then mixed some 65C water and compared it to my HLT dial thermometer and two glass ones. So my 66C mash was actually 68C maybe even a bit higher if I overshot a bit. Still a bit hard to believe that this would cause my dunkel to finish at 1.030 with a hungry yeast like WLP300, might have also under pitched a bit, combined with the low 17C ferment temp.........

[Matt Smith]

Glad you found the prob. Lower mash temp next time conbined with a bigger pitch as other mentioned and you should be all good!

I don't trust thermometers, like you found, every thermometer Ive had has read different, so now I just have a single mashmaster dial thermometer that I use for everything. It's one of the weldless kit ones that's meant to go through wall, but I just use it as a handheld and I calibrate it with boiling water at least every 3rd brew.

[Scott Lyon]

yep, Mashed at 64 today, and pitched all the slurry from the bottom of the Dunkel into 40 litres of Hefeweizen, fingers crossed!

[Grant R Baker]

I know you are targeting 17C but the rating for fermentation of the yeast is 20-21C.

I would up it now to 21C... fermenting a temp too low can cause stuck fermentation just like you have mentioned. There is nothing wrong with starting low but you'll probably need to increase the temp slowly (about 1 degree per hour or so is slow enough).

[Gareth Kerr]

It looks like you may be under pitching a bit there, although even then I'd have expected it to get a fair bit lower than 1.030. Combine that with the slightly lower temperature and the yeast might not be too happy.

At 750000 cells/ml/deg plato you're going to need 750000*24000*13 = 234 billion cells for a healthy ferment.

Going with yeast calc starter numbers, you've either got 131 billion (no aeration), 164b (shaking), or 197b (stirplate). You didn't mention your starter aeration method, but if it was a stirplate then I'd imagine the 200b cells or so would be enough really, and certainly not short enough to cause such under attenuation. At the other end of the scale, 131b from no aeration is a pretty big shortfall.

Either way, just wait it out, no need to panic yet.

DISCLAIMER: And yes, I'm sure there will be plenty of anecdotal "I did X gravity beer and pitched 1 packet of Y and it fermented out fine" as most tinternetz yeast threads seem to contain, but if you're under pitching constantly then you'll likely get lucky most of the time, but maybe not all of the time.

[Des Ross]

Mmmm...i would have thought a 24 Hr old 1L starter with SG 1.035 pitched into 24L of wort with SG 1.052, would have been more than enough..

[Peter Smith]

 I have made 4 different wheat beers on the trot   3068, 3056, 1010 and a us06  all over last few months on garage floor at 17 ish  sometimes 15,  I have found they all grind down, always leave them for 3 weeks, they where all 2L starters as I am not much into banana beer.  Its very strange as these types of beer/yeast can be monsters if warm, and they say if you underpitch you get more esters, nothing about under attenuation mentioned. I dont temp control my wheat beers as have never had issues.

[Grant R Baker]

You will if you ever use M44.. fussy yeast that one.

[Peter Smith]

I did a milk stout with 1084 and spare 5L with m44 for giggles, bottle them later this week.... was going to use m44 repitch in a big ipa but I didnt like the way the ferment looked for the m44 and since there was so many $$$ worth of hops I chickened out and went us05.   sat at 19/20 all the way through...

will do a sg tonight