BeerBorg

For quite a number of batches, I've noticed this trend: I usually hit my OG pretty much. Maybe a bit higher or lower, but nothing unusual. But my FG is coming in really low. I don't have exact numbers for any batches, but if my OG is 1.056, for instance, I'd expect an FG of 1.014. But, after 3 weeks of fermentation, I get a reading more like 1.006 or even lower. This has been occurring fairly consistently for a while, regardless of fermentation temperature, yeast strain, style, or whatever other factors might be in play (and I've tried to consider all of them).

I can accept some variations in OG and projected FG, given temperature variations, differences in volume, etc. But this seems to be a consistent inconsistency.

Any ideas?

< === Experienced something similar recently.

Turned out the piece of paper inside the hydrometer had slipped.
Back to normal after a recalibration.

I have had what I thought to be bottle infections that dried out the beer over time, adding carbonation but no bad flavor that I could discern.

If the OGs are matching up with the same hydrometer, then the expected attenuation would still be whatever % of that OG.

If what Dave is saying is that the OGs are where they should be but he's getting 80-90% attenuation from that measured value with the same hydrometer, instead of an expected 70-75% or whatever... then it's not just the paper has slipped, as that would also throw off the OG reading too.

If two different hydrometers, IE you have a fancy 3 piece high definition lab style set where one is a high gravity scale and one is a low gravity scale, then that could be it though.

If not...

Maybe your thermometer used for mashing is off and you are mashing a lot lower temp then you think.

Or have you brewed with Bella Saison lately? Maybe a little bit is still alive... it will do that, or what John above describes...

Especially bottle infections. Bella/French Saison sometimes coats the bottles interior with a film. It is easy to not get it all out / dead, especially if you don't bake your bottles...

mashani wrote:Maybe your thermometer used for mashing is off and you are mashing a lot lower temp then you think.

This was my first thought.

Can't be the hydrometer, for the reasons Mashani gives. Impossible for the paper to slip back and forth between every OG reading and every FG reading.

I doubt it's the yeast. I made a saison a few months ago, but this phenomenon is across the board with all the batches I make; not just the batches made in the carboy that fermented the saison.

Could be the thermometer, but I kind of doubt it. Wouldn't my mash temperature have to be a good five/ten degrees cooler than what the reading is? I've checked the temperature throughout while waiting for the boil, and it seems accurate.

Maybe it's my grind.

I always project 75% conversion, and it's always worked out pretty well in the past, but maybe I'm just getting better efficiency, for whatever reason.

4 degrees could make a difference in fermentables from the mash.

FedoraDave wrote:I've checked the temperature throughout while waiting for the boil, and it seems accurate.

Knowing for sure is half the battle. Like Steve said 4 degrees can make a huge difference.

Dave, you may be onto something with your crush. I read somewhere (here, maybe?) of guys getting high attenuation with BIAB. I think the theory is that a finer crush allows quicker extraction, therefore more time for conversion. Try a shorter mash?

FedoraDave wrote:Can't be the hydrometer, for the reasons Mashani gives. Impossible for the paper to slip back and forth between every OG reading and every FG reading.

Wasn't suggesting the scale slides back and forth between readings.
Just b/c the OG is what you expected doesn't mean the instrument is accurate.

It is odd without any sort of change in your process. I've had exceptionally high attenuation all along. It must be something in the process or maybe each kicks in just a little... temp control, nutrient, aeration, etc. A few years back I just started mashing a few degrees higher than normal to compensate and that has worked out well.

HerbMeowing wrote:

FedoraDave wrote:Can't be the hydrometer, for the reasons Mashani gives. Impossible for the paper to slip back and forth between every OG reading and every FG reading.

Wasn't suggesting the scale slides back and forth between readings.
Just b/c the OG is what you expected doesn't mean the instrument is accurate.

But the FG will also be off by the same proportional amount (within expected attenuation % tolerances).

So if OG pretty much always matches what you expect but FG pretty much always does not (which is what Dave seems to be saying), then it's not this.

If both are always off, then yes, the hydrometer is a pretty good bet.

FedoraDave wrote: Maybe it's my grind.

I always project 75% conversion, and it's always worked out pretty well in the past, but maybe I'm just getting better efficiency, for whatever reason.

This would increase your OG, and not just decrease your FG. It should actually make you FG higher since your OG would be higher, unless your mash temps are lower too.

Mystery solved. It was the thermometer. I checked the old one against a new one (fresh out of the package). Same manufacturer/model digital thermometer. Compared air temps between the two, and old one was three or four degrees blow the new one.

I have since consigned that particular thermal measurement device to the flames. We'll see what happens going forward.