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Over Attenuation

New problem I have run into (I think). Pretty much hitting my OGs but my FG is coming in way below what is predicted in Beer Tools. For example, I made an American Stout with an OG of 56 and it came out about 6.4% ABV using SAFAL 05. Getting this pretty much across the board. I am brewing on a stovetop so maybe the extra time it takes to get it to temperature is overmashing? Also just started using a stirplate with generous amounts of recycled yeast and am getting great fermentations. My last Vienna Lager came out thin, but I may have let it run too long. Ideas?

US-05 often finishes pretty low, so that’s probably at least partly responsible.

How sure are you that your thermometer is accurate,
And you’re not mashing in the mid/low 140’s?

I thought about the thermometer too. I used another one which showed the thermometer on my brew kettle was 2 degrees low. Of course, the other thermometer may be the one that’s off. I have raised my brew temps by 2 degrees to offset but pretty sure I am not off by 10 degrees.

Beertools doesn’t adjust the anticipated attenuation based on the yeast strain you select but instead you adjust that manually. US-05 typically finishes pretty dry so the default (75%) will usually be lower than actual. The Fermentis web site says finishing gravity is “medium” for this strain but I didn’t see an attenuation percentage listed. The Beertools software shows a range of 72-78 percent for attenuation. I’ve found that I get up to 83 percent sometimes. Pitching more yeast or using a yeast starter doesn’t affect it much. I often over pitch US-05 and if anything I finish a point or two higher when I do this.

I manually changed the attenuation to 83% and the FG came out on the nose. Could just be good yeast fermentation that I need to account for. I mashed the stout at 155 to balance it so should be pretty good and hopefully not thin.

I had the same problem for a year. I finally bought a calibrated and NIST traceable thermometer and found my two thermometers were reading 3-4 degrees F high. I don’t recall the make but the model is ‘lolipop’ - search Amazon, you should find it for about $20. If not the thermometer, then your mash may not be equilibrated when you check the temp. My procedure is to add the strike water to the tun and let it sit for about 30 minutes to equilibrate. Then I adjust to strike temp. Works for me.

To clarify, I get as high as 83% from that yeast, meaning that’s what I get when I’m trying to get a low FG by mashing around 148-150 for 1.5 hours. At 155 for an hour my attenuation would be a little lower. I usually have to get up around 158 to see a significantly higher FG, but that’s with my thermometer, equipment, process. As bwmac2 mentioned, you may want to check your temp. readings / accuracy for future batches.

Consistency is more important than accuracy IMO. You can try mashing at 158 or 159 (using your current equipment and method) next time to see what effect that has. If 158 is actually 155 you might get the results you’re looking for with that temp. As long as it’s repeatable, predictable and something you control, that’s what really matters in the end.

ANY software that attempts to predict attenuation is only making a guess based on the attenuation rating of the yeast. That rating is for comparing one yeast to another and is not necessarily accurate in predicting the attenuation you’ll get. That’s much more dependent on the fermentability of the wort (recipe and mash temp) that the rating if the yeast. In short, I’d advise ignoring any FG prediction made by software.

Denny-makes sense. Having said that don’t want the Helles in the fridge fermenting to over attenuate and end up thin like the Vienna. What is good rule of thumb to start pushing temperature down below 50 degrees? OG was 1.050 and fermentation is strong starting day after I pitched. Thinking of starting temp down on day #10 (Wed).

If you’re talking about deliberately stopping fermentation, I wouldn’t. That’s just asking for off-flavors, especially with a lager strain.

I was having a string of lower-than-usual FG’s. Discussed it with my LHBS and mentioned I had been working through a bulk sack of Pilsen malt. He pointed out that using a Pilsen malt for base is going to give me a more fermentable wort compared to Pale/2 row…all other things being equal. Just thought I’d throw that out for consideration…

I dunno…did he explain why? I’m skeptical.

He simply said that Pilsen will produce a more fermentable sugar profile than standard 2-row or pale. I guess it made enough sense, from my general and limited notion of what a pilsner is, that I didn’t push it. Again, just throwing it out there as a data point, some guy’s opinion. Not even 2 cents, more like a penny.

It could just be that the LHBS owner was familiar with the two malts in question and knew that from experience. I doubt it would hold up as a general rule though.

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