Not reaching target final gravity

[feldschlossen]

I've been all grain brewing for about 20 batches now. I have often (with many different beers) run into the problem of not fermenting down to my target final gravity. For example I recently brewed a Hefeweisen using 5.50 lbs of 2row and 4.5 lbs of flaked wheat. The original gravity was 1.047 and the target final was 1.013. I pitched at 65F with a big starter. The fermentation was rolling very strong by the next morning and the temp was up to 68F. Fermentation had pretty much stopped by the fifth day and I checked the final gravity on day 15. I reached 1.023. Substantialy higher than my target of 1.013. I have tried in the past to restart batches like this with fresh yeast. In the end I got no more fermentation. I'm thinking that I must be producing too many unfermentable sugars some how. If this is the case what could I be doing to cause this? I am mashing in at 154F and mashing out at 168F.

[MikeB]

What is the average attenuation for the yeast you are using? Maybe use different yeast if ave atten. is low.

When you say big starter what size? mrmalty.com yeast pitching rate calculator can help with pitching the proper amount of yeast

How long are you mashing for? Increasing mash time especially when mashing at low temps can help with conversion.

What are the flocculation characteristics of the yeasts that you are having problems with? You may need to swirl the fermenter for certain strains.

How are you measuring your mash temp? You may have hot or cold pockets in your mash, so you may want to take temps at different areas of the mash tun.

Have you calibrated your thermometer lately? I suspect this is not the problem, but it might be good to check this.

This recipe doesn't look problematic in terms of fermentability, but certain malts (like crystal malts) are not very fermentable. Limiting the amounts of these types of malts can help improve fermentablility.

[brewinhard]

I would most definitely check your thermometer. Be SURE it is properly calibrated and brew again!

[Kbar]

+1 on checking mash temps. I was 2-3F high so I was getting full bodied beers, but not much for the yeast to munch on and convert. Brought it down and so did the FG's.

[Fremont Brewer]

Another possibility not mentioned yet might be an oxygenation problem. Are you aerating your wort somehow? I know I ran into this issue. I thought i was fine just splashing around the carboy really good, and I usually was, until I made my first lager. My first lager I attempted to make was a dopplebock. I had plenty of yeast, but my ferment fell short. Since then, I have been using an aeration stone and aquarium pump, cost about $30 at MoreBeer.

John

[Quin]

Another possibility not mentioned yet might be an oxygenation problem. Are you aerating your wort somehow? I know I ran into this issue. I thought i was fine just splashing around the carboy really good, and I usually was, until I made my first lager. My first lager I attempted to make was a dopplebock. I had plenty of yeast, but my ferment fell short. Since then, I have been using an aeration stone and aquarium pump, cost about $30 at MoreBeer.

John

+1000.

[Wutz]

Did the fermentation temp drop after it reached 68º?

A dropping fermentation temp has been my culprit when I'm coming up a little bit short on my FG.

...but you're not coming up a "little" short. You're coming up quite a bit short. Maybe a combination of dropping ferm. temp and a non-calibrated thermometer?

I have no idea, though. I just wanted to bring the fermentation temp. up since I've had a little experience with that.

[CRBrewHound]

Start with the two most common events that cause under attenuation.

Pitch the proper amount - this means almost always making a starter

Control the ferementation temp - yeast like it warm, they produce lots of off flavors but they are most effecient when warm. Make sure you are ferementing at warm enough temp. If you ferment in a basement make sure it is not dipping down in the evening to temps below a good ferment temp, then kick it up at the end of ferementation to get them to eat the last little bits of sugar.