attenuation issue

[mr.jay]

Before I go ahead and email White Labs, I thought I would do some collective trouble shooting here (since yeast may not be to blame).
I'll get right to it.....Here are the stats:

Brewed a stout using (5th generation) Bristish strain I use, quite often with superb results.

O.G 15.1 Plato

75% British Pale malt
13% Dark malts (Chocolate, Roasted and Patent)
6% 60L Crystal
6% Carapils

Infusion Temp: 154 (1) hour

Fermented at 65F

YES I oxygenated correctly, YES I knocked out at 70F

Gravity dropped to 6.5 in 8 days. Not to shabby. Fermetation has slowed down to almost a dead stop 6 days later, gravity only 5.4

I wanted this to be a dry imperial style stout. Ironically, with all that sugar still in it, it's not at all sweet! It tastes like a well attenuated dry beer! That's when I began to suspect my hydrometer being off. I checked another beer, and it seemed spot on.

I thought maybe (since I never brewed a stout to this caliber) it was my formulation. With only 6% crystal, I don't see how, especially at 154 degrees . The dark malts shouldn't leave behind that much residual sugar either.

Then I thought, maybe I under-pitched, or harvested too early.

I also thought, maybe I shut a previous beer in too early, and put the yeast under too much pressure (that did actually happen...Ooops )

Either way, I ordered more yeast. My question is:
(1) What do you suspect happend here
(2) Why does the beer seem so dry, when the hydrometer says different.

Thanks,
Jay

[kugeman]

I ran into a similar problem several years ago. It turned out that my mash tun thermometer was off (by 6 degrees!). Have you checked all of your temperature probes to make sure that you actually mashed and fermented at the temperature you intended to?

just a thought...

[gabewilson50]

Darker beers tend to mask sweetness, so your stout may seem dry despite having plenty of residual sugars. It's especially evident when you taste the wort. The first few times I brewed a darker beer, I tasted the wort before checking the gravity and thought it would be somewhere around 12 Plato but it ended up being over 16 Plato. I had to train myself to not freak out when I didn't taste a super sweet wort when I brewed that beer.

[jarviw]

I double Kugeman. Check your thermometers!

Also, always, a good practice is to pre-determine your final attenuation with a small amount of wort (say, 1/2 pint) and a huge dose of yeast on the side. it will give you a good idea if the fermentation is going right.

[mr.jay]

How does one test a thermometer's accuracy on a MV? (sorry if it sounds like a stupid qu.. It just never occured to me this could be a problem, so I never thought about it).

[kugeman]

I suppose it depends on how your mash tun is designed, but on mine I just removed the thermal probe tri-clamp, and then unsrewed the housing around the actual thermometer. Then just drop it in a bucket of ice water and presto! I usually put another thermometer that I know is accurate in the ice water to make sure that I'm getting a true reading. Once I determined it's accuracy (or innaccuracy) in ice, I usually pull some water from the hot liquor tank to test the accuracy in mash ranges (155 F) just to double check.

[liammckenna]

testing thermometers

bucket of ice with a little water = 0C

boiling kettle = 100C

Pax.

Liam

[GarySped]

It is a bit more involved than that - testing of thermometers. In Denver water does not boil at 100 C because of the pressure. Same reason baking has to be done a little differently there.

Look at the ERTCO (Everready Thermometer Co) for advice on temperature and correction.

[Sauce]

Yea...you definately want to test it in the range that is used. Thermometers do drift a degree or two or three between 32f and whatever your boiling point is.

Ive looked a few times for a precision lab grade calibration thermometer but I never got one...cant remember if I couldnt find one or was just freightened by the price.

[mr.jay]

Thank you, everyone. Cleaning the entire brewhouse tomorrow, will check it then.

Thanks!
Jay

[Mitch Steele]

I second the idea of doing a forced fermentation on the wort to test what your final gravity should be. It's a very valuable test that in 24 hrs can tell you whether you've got a mash temperature problem or a yeast problem.

I also recommend checking cell counts during the fermentation, if the yeast cells aren't remaining in suspension, the fermentation will hang.
A viability check on youir yeast will also help determine the cause.