Gravity finishing lower than expected

[Beer-lord]

My last 5 beers all had the FG finish a good deal less than the recipe predicted. Not a huge deal as the beers are awesome but as I've tried to brew a bit lower ABV beers, this gets in the way. I always have very fresh yeast (usually a starter), over pitch, I add yeast nutrient the last few minutes of the boil, and though I use a pump to go into the fermenter and it does a good job of aeration, I do a 45 second or so hit with some oxygen. I'm thinking all of this, especially the extra aeration, is allowing the yeast to attenuate more than expected.
Does this all make sense?

[berryman]

This is a good question because I sometimes have that problem too. trying for 1.015-.020 and FG comes out 10-12. Maybe to low mash temp.? IDK but would like to know too.

[mashani]

My last 5 beers all had the FG finish a good deal less than the recipe predicted. Not a huge deal as the beers are awesome but as I've tried to brew a bit lower ABV beers, this gets in the way. I always have very fresh yeast (usually a starter), over pitch, I add yeast nutrient the last few minutes of the boil, and though I use a pump to go into the fermenter and it does a good job of aeration, I do a 45 second or so hit with some oxygen. I'm thinking all of this, especially the extra aeration, is allowing the yeast to attenuate more than expected.
Does this all make sense?

Oxygen and nutrients control how many extra "growth phases" the yeast can have in your fermenter from the original pitch rate before the metabolism switches to active fermentation. If you are already pitching a hefty overbuilt starter to begin with, and then add enough extra nutrients and oxygen to allow for more then the 1-2 ideal growth phases post pitching, then that 3rd or 4th growth phase could amount to some ginormous amount of yeast (remember it doubles every phase, so 2 billion becomes 4, then 8...). Or even if not, that 2nd normal ideal growth phase is increasing your starter by as many cells as you overbuilt and pitched by a factor of 4.

The yeast switch metabolism when they run out of what they need to grow (the oxygen and nutrients). If your wort is high in FAN to begin with due to grains used, yeast nutrients are likely not even needed for "normal" growth. It would be more adjunct oriented beers that would need them.

So yeah you might be ending up with a "metric shit ton" of yeast that just chew up everything instead of petering out.

[Beer-lord]

It's also likely my OCDness is involved.

[BlackDuck]

What kind of brewing software are you using? If your getting these results consistently, you can always adjust your brewhouse efficiency on the software to match your last few results. Then, use the new efficiency number in your next few recipes and see how they compare to what the software is telling you should get.


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[Beer-lord]

I'm still using Beersmith and have been importing in Brew Father and they are exact. Pretty much what I've been doing for years. I've checked my temperature to make sure the mash is accurate and it is. All of these beers have been mashed at between 148 and 152. I've made no changes in settings other than to crush slightly tighter.

[BlackDuck]

That’s exactly what I’m getting at. Increase your efficiency setting a couple percentage points on your next batch and see if you finish closer to what the software says you should. Something is getting you better efficiency. Maybe it’s the crush, maybe it’s fresher yeast, maybe it’s the yeast nutrient. Who knows. But by adjusting your efficiency number, you might be more likely to write your recipes to hit your numbers more closely.


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[Beer-lord]

This, I shall do.
Thanks.

[mashani]

That’s exactly what I’m getting at. Increase your efficiency setting a couple percentage points on your next batch and see if you finish closer to what the software says you should. Something is getting you better efficiency. Maybe it’s the crush, maybe it’s fresher yeast, maybe it’s the yeast nutrient. Who knows. But by adjusting your efficiency number, you might be more likely to write your recipes to hit your numbers more closely.
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He should be seeing a higher OG though as well if it is brewhouse efficiency. I was under the impression he was just seeing a lower FG?

[Beer-lord]

Mostly, yes but sometimes I do have a higher OG as in my most recent beer.

[HerbMeowing]

BeerSmith 1.4 always predicts a higher FG by 2-4 points.
not an issue b/c I prefer the drier finish with FG between 10 and 12 ...

[mashani]

BeerSmith 1.4 always predicts a higher FG by 2-4 points

It is really very yeast dependent (not just pitch rates either), different yeasts will perform differently in various wort conditions. Best I think ultimately just to track your batches with a particular yeast and come up with your own guess if you want to be picky.

I generally just don't worry so much about it. Regardless it's beer.