Streak of overattenuating fermentations...

So, as the subject suggests, my last few brews have overattenuated while fermenting. Some by only a couple points, some by considerably more.

To be exact, this started 4 batches ago, and has been happening ever since, and I'm not able to put my finger on a cause - though I've started to form a suspicion.

It started with my Pumpkin Ale. I went with a very slightly modified form of the Thunderstruck Pumpkin Ale recipe found right here on HBT (scaled up slightly, tweaked for the efficiency I get on my system, then grain weights tweaked into round-ish numbers for LHBS friendliness). Anyway, that one had some issues with it - bad grind from the LHBS (a few guys in my club have been having similar issues) so I had to add some DME to reach my expected OG, so I figured that'd impact the fermentability of my wort. But I figured it'd be slightly less fermentable, not more. Beersmith projected a FG of 1.016, actual FG was 1.007! The beer definitely does not taste like a 1.007 beer - but that may have something to do with the pumpkin helping out the mouthfeel... This was fermented with S04.

Anyway, the next beer was an American Stout. Short story: projected FG 1.014, actual 1.010, fermented with Wyeast 1056.

Following that, was an English Mild - projected 1.013, actual 1.009, fermented with Wyeast 1968. Kind of a big miss for a mild.

And the latest, a winter warmer, projected 1.014, actual 1.010, again with 1968 (actually the same yeast cake from the Mild).

So - each of these has been all grain brews, each has been batch sparged. In each case, except the winter warmer, the batch sparge has been split up into two equal amounts (the winter warmer, I decided to just go with what Beersmith was telling me and I went with 4 equal amounts and see what I got).

One suspicion I had was that I had been letting my runnings cool, and perhaps some amount of conversion was still occurring there, so with the winter warmer, I made sure to fire up the burner for my BK as soon as I had drawn off my first runnings and at least get those up to mash-out temps. However, I wasn't paying close enough attention to my HLT - I cut its burner at one point when it was approaching the high 170's, and never really watched it again, until we were about to pull the water for the 4th batch sparge, when my buddy observed the water had dropped to the mid 150's. So, I'm suspecting that maybe the grain bed never quite stopped converting? Maybe this has been my problem all along?

So, my questions are: Am I on the right track and, if so, how can I correct this? If the grain bed is still going through conversion during sparge, should I just shorten my mash rest from 60 minutes to 45, and figure that the conversion during the sparge is going to account for the shortened mash rest? Or is there some other factor altogether that I might not be accounting for?

You will need to hit a mash out temp of around 170 degrees during extended sparging to stop conversion. Any cooling after that shouldn't matter since the enzymes would be denatured.

How are you measuring gravity? Have you checked the calibration of your instrument? You did notice that all three batches were off by the same 0.004 gravity points? This would lead me to believe it was an equipment issue.

Check the accuracy of your thermometer too.

Mash temps, time mashed or grain left at conversion temps, and to a lesser extent, yeast health/pitch-rate.

I do 3-8 hour mashes and the longer time at conversion temps DRASTICALLY affects my fermentability. I had a 153 mash that attenuated to 1.001. Obviously you're not doing this long of a mash, but I had to make changes to mash temps to get the profiles I needed. Your prolonged sparging could be affecting conversion as well.

Heat up your sparge water to 180-190. If you're doing multiple sparge additions, the thickness will be plenty to have good PH and you're adding a small amount, so temp of grain bed won't rise drastically. The goal is to heat the bed to 170 on the first sparge addition. After that you can let the rest of the sparge water come down to 170.

pvtschultz said:

You will need to hit a mash out temp of around 170 degrees during extended sparging to stop conversion. Any cooling after that shouldn't matter since the enzymes would be denatured.

How are you measuring gravity? Have you checked the calibration of your instrument? You did notice that all three batches were off by the same 0.004 gravity points? This would lead me to believe it was an equipment issue.

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Well, three out of the four were off by exactly four points - the pumpkin was considerably more than that!

Yes, I've tested (and re-tested) my hydrometer, and I know it to read 2 points high and I correct all my measurements accordingly, so that much is being accounted for.

I'm fairly certain I'm not raising the whole grain bed up to 170 (or even 168), as I'm following Beersmith's recommendation to add sparge water at 168F to the grain bed. I'm no thermodynamacist (sp?), but I'm pretty sure that adding water at that temp to a grain bed at 154-ish (some of those mashed a little lower, some a little warmer) isn't going to raise the grain bed all the way to 168. I've read a lot of discussions on how important a true mash out is or isn't, and I'm starting to lean towards the "is" camp I guess...

I'll also grant that, as Golddiggie pointed out, I haven't checked the accuracy of my thermometers (either the one on my HLT or the one I'm using to check my mash temp) recently either. I should probably make that a priority before next brew day.

Thanks for the input so far - keep it coming!

stratslinger said:

Well, three out of the four were off by exactly four points - the pumpkin was considerably more than that!

Yes, I've tested (and re-tested) my hydrometer, and I know it to read 2 points high and I correct all my measurements accordingly, so that much is being accounted for.

I'm fairly certain I'm not raising the whole grain bed up to 170 (or even 168), as I'm following Beersmith's recommendation to add sparge water at 168F to the grain bed. I'm no thermodynamacist (sp?), but I'm pretty sure that adding water at that temp to a grain bed at 154-ish (some of those mashed a little lower, some a little warmer) isn't going to raise the grain bed all the way to 168. I've read a lot of discussions on how important a true mash out is or isn't, and I'm starting to lean towards the "is" camp I guess...

I'll also grant that, as Golddiggie pointed out, I haven't checked the accuracy of my thermometers (either the one on my HLT or the one I'm using to check my mash temp) recently either. I should probably make that a priority before next brew day.

Thanks for the input so far - keep it coming!

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See my post above. Also, consider mashing thinner so you don't have so many sparge additions. You're prolonging not only your brew day, but your conversion process. I mash as thin as I need to in order to get the same strike and sparge volumes. I then just run off what I have in the tun, and add all of my sparge water at once, then run that off.

You know, now that I look closer at my notes, another thing comes to me - and tre9er just hit it on the head!

The Pumpkin ale was the first brew I did where I used Beersmith to formulate my recipe and my brewday checklist. And I did everything, including sparge temperatures, going by Beersmith. Looking at the last beer I did previously, using Brewtarget, I see that I used considerably warmer (close to 180) water for my batch sparge, effectively performing a mash out. Sonofagun. Meanwhile, looking at the brewday instructions Beersmith has generated, each one has had me perform my batch sparge with 168 degree water.

I think we may be onto something!

stratslinger said:

You know, now that I look closer at my notes, another thing comes to me - and tre9er just hit it on the head!

The Pumpkin ale was the first brew I did where I used Beersmith to formulate my recipe and my brewday checklist. And I did everything, including sparge temperatures, going by Beersmith. Looking at the last beer I did previously, using Brewtarget, I see that I used considerably warmer (close to 180) water for my batch sparge, effectively performing a mash out. Sonofagun. Meanwhile, looking at the brewday instructions Beersmith has generated, each one has had me perform my batch sparge with 168 degree water.

I think we may be onto something!

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And if it took you an hour to do all of your sparging, you were still mashing that whole time, effectively.

I do overnight mashes and while I do go a point or two below what beersmith says its never much below that. It seems a little strange to me that just sparging longer or not getting all the way to 170 would make your wort that much more attenuative. But I guess its possible. One thing that helped for me was getting the thermopen. After getting that baby my attenuation numbers are more in line with beersmith was figuring for me.

jtejedor said:

I do overnight mashes and while I do go a point or two below what beersmith says its never much below that. It seems a little strange to me that just sparging longer or not getting all the way to 170 would make your wort that much more attenuative. But I guess its possible. One thing that helped for me was getting the thermopen. After getting that baby my attenuation numbers are more in line with beersmith was figuring for me.

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Do you adjust your mash temps at all? I've had to increase mine by 3 degrees on average in order to get lower attenuation.

Maybe a tad bit more I generally go 152-153 on most ales. 150-151 for IPAs and lagers. I used to have the super attenuation issue as well (before I was even doing overnight mashes) and to me I think it was a combo of thermometer maybe not being exact and yeast health/sanitation.

Weird though. For me this happened no matter the yeast, only on overnight mashes, and only solved it by raising temps 3* for mashing.

Yeah I might stop doing it in the winter months here as I think the summer nights helped my mash maintain a decent temperature.

jtejedor said:

Yeah I might stop doing it in the winter months here as I think the summer nights helped my mash maintain a decent temperature.

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I usually drop 10 degrees overnight in my cooler, wrapped with blankets. I'm fine with the way it's working but that first beer I mashed at 153 overnight and attenuated to 1.001 I was like but in all honesty, it turned out great for a hop-burst PA, not hot/alcoholic at all even though it was over 6% (supposed to be a session!)

You mentioned that the beer doesn't taste as though it had a very low FG- as infuriating as it can be to miss the mark statistically- if you're making solid, drinkable beer then don't worry about it. That's how I would feel anyway. Maybe buy another hydrometer or borrow a friends and use it to see if yours wasn't off a tad bit. ( I know you said that you checked and rechecked yours, just an idea.)