Over-attenuation(extract)

Hi guys, I've brewed about 6 batches of extract so far, and I've incorporated more and more techniques that I read on here with each batch. With my recent batches I've started fermentation on the cool end of the yeast spec and then after active fermentation starts to slow, I'll bump the temperature up a few degrees slowly("diacetyl rest" maybe). After that, I'll let it get cold again("cold-crashing" perhaps).
I feel this has really helped my beers get down to a lower FG, but it appears as if they're over-attenuating. My latest example:
Innkeeper extract 5 gal. batch from Northern Brewer
Wyeast 1469 with a ~700mL yeast starter
Attenuation spec: 67-71%
OG: 1.043 (after temp. correction)
FG: 1.004 (after temp. correction)
Apparent Attenuation: 90%

I haven't calibrated my hydrometer with distilled water recently, but I did use tap water @ 60 and my hydrometer read 0.998, so I don't think it could be too far off.

On one hand, I'm happy to get the extra ABV, but on the other I'm afraid it will make the beers taste too "watery" and not full-bodied. What do you guys think?

Thanks,
Andy

I didn't know you had to calibrate hydrometer! Let me know more? Or you talking about refractometer?

I doubt you're overattenuating from a massive overpitch. For a 5 gallon batch of 1.043 using 1 pack of 1-month-old liquid yeast, you'd need approximately 1.5L of simple starter or 750ml of a stir plate starter just to hit the sweet spot.

Like benco, like phrase "calibrated hydrometer" throws red flags. I'm thinking this is a measurement or calculation error.

Do you mean refractometer? If so, did you apply correction for alcohol content? Are you measuring in Brix and making a calculator conversion?

Hydrometers can't be calibrated because you can't adjust them, but they can and should be checked with 60 degree water. Refractometers need to be calibrated and IMO should always be checked against a hydrometer, but they always read high for a FG reading until you run the adjustment formulas, not low.

Good point, "calibrated hydrometer" was a poor choice of words. I'm trying to say that my hydrometer is not likely significantly inaccurate.

Andy

bottlebomber said:

Hydrometers can't be calibrated because you can't adjust them, but they can and should be checked with 60 degree water. Refractometers need to be calibrated and IMO should always be checked against a hydrometer, but they always read high for a FG reading until you run the adjustment formulas, not low.

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I've had "attenuation problems" with my dual-scale ATC refractometer when I read the OG in SG and then the measurement for FG in Brix. Cheap refractometers like those found on eBay use a SG scale that doesn't compensate for the non-simple-sugars in wort, so you can use either scale, but you must stick to that one. In that case, it looked as if I had a 91% attenuation, when in reality I had a spot-on 74% attenuation using Chico strain.

Doesn't look like that's the case here since the OP confirmed he's using a hydrometer.

OP, are you sure you read the hygrometer correctly? 1.014 would be easy enough to read as 1.004, and it would be a 67% attenuation.

thadius856 said:

OP, are you sure you read the hygrometer correctly? 1.014 would be easy enough to read as 1.004, and it would be a 67% attenuation.

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I can't be 100% sure, and my sample is my stomach now, but I see your point(I could've quickly interpreted the "10" as 1.000 instead of 1.010). At this point(bottled) is there any way to check, i.e. will the added sugar significantly throw off my SG reading?
I'm contemplating whether it's worth it for me to waste a 12 oz. beer to check the SG.

I wouldn't say it's worth the bottle. It's your call though.

I'd just wait until conditioned, take enough for a sample, and drink the rest. Be sure to let it warm and shake out some CO2 before measuring again.

Good luck.

Minor point here, but you can and should calibrate your hydrometers. Calibrate may not be the technically correct term, but the principle is the same...ensuring you know how to read your hydrometer. To "calibrate" one, simply float it in distilled water at 60 degrees. If it's properly calibrated, it will float at 1.00. If not, it will be either higher or lower than one and you must always include that variation when taking a reading. Otherwise, your readings will be consistently wrong.

I think "correcting" or "determining correction value" would probably be a pretty suitable term.

thadius856 said:

I'd just wait until conditioned, take enough for a sample, and drink the rest. Be sure to let it warm and shake out some CO2 before measuring again.

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I'll probably wait about 2 weeks before I measure. I'm thinking I probably did mis-read the hydrometer.
1. How much will the CO2 affect the SG? I'm assuming all the sugar will be CO2 by then and won't affect the SG, right?
2. Hypothetically if my FG was really 1.004, what would be a potential cause? Or is it impossible?

Thanks,
Andy

1. Shake the warmed sample for a minute before taking the gravity. All CO2 will fall out of solution, giving a clean reading. Sugar should be gone if they're full carbed. You'll have to "mouth test" the other 9 oz or so of the bottle to determine if residual sugars are gone and the carbing is completed. Poor you.

2. Fermenting too warm for an extended period of time, wild yeast, or infection.

I've confirmed my FG reading was indeed 1.004. I've also confirmed that the beer tastes good :cross:.
I think what's throwing the attenuation calculation is the 1 pound of dextrose in the recipe; I didn't mention that earlier because I hadn't realized it's impact.
My calculations have 34.35 points from malt, LME, or DME, and 7.4 points from the 1 pound of dextrose.

Lesson learned: Simple sugars affect your attenuation differently than malts.