Not hitting final gravity when using blow off tubes

[Phoenix1854]

Hey all, I am encountering a weird problem or maybe it is not a problem at all. I brew 1 gallon batches and use the standard 1 gallon glass carboys. Most of my beers need a blowoff tube for the first 72 hours of fermentation when the yeast goes crazy. Once it slows down, I replace the blowoff tube with a standard airlock. The problem is, most of the actual fermentation seems to stop after that initial activity. I check the gravity periodically throughout the next week or so and it barely moves and never reaches its final gravity. On the other hand, beers that do not need a blowoff tube always reach their final gravity.

One thing I have noticed is that there is always lot of yeast that escapes through the blowoff tube and into the cup at the end of the tube. Could that be a reason I am not hitting final gravity for beers with blowoff tubes? Generally I am within 0.5-1% of what I am aiming for, but it never quite gets there. I never under pitch the yeast and each beer ferments at a constant room temperature with little fluctuation (66-69). The beer generally turns out pretty darn good regardless, so maybe my refractometer is off.

 

[Kahler]

I could be totally wrong, but the yeast that stays in the fermenter would multiply and take care of the "lost" yeast in the blow off tube.
How much headspace are you leaving?
What are your typical OG's and FG's?
Recipe?
All grain? Extract?
Being within .5-1% isn't a problem, sounds like you're doing a good job.

 

[VikeMan]

So, examining this a bit... I assume the batches you are using blow off tubes with tend to be higher gravity worts. Is that the case? If so, do your higher gravity batches happen to have grain bills that contain a higher proportion of specialty malts? Do your blowoff batches use different yeast strains than your non-blowoff batches? And, where are your expectations for final gravities coming from?

 

[tracer bullet]

Agreed to the above and want to add - refractometer - not good for measurements w/ alcohol in them. Not without conversion work at a minimum. I use a hydrometer myself, the refractometer gets put away once I pitch yeast.

 

[Phoenix1854]

I could be totally wrong, but the yeast that stays in the fermenter would multiply and take care of the "lost" yeast in the blow off tube.
How much headspace are you leaving?
What are your typical OG's and FG's?
Recipe?
All grain? Extract?
Being within .5-1% isn't a problem, sounds like you're doing a good job.

I definitely pitch enough yeast and I assume that I have enough yeast left in there to finish the job. As for headspace, I usually fill hit the "One Gallon" marker on your typical 1 gallon glass carboy, or just below it. So I think there is enough.

I recently brewed an all grain robust porter with an OG of 16 Brix (1.063) and it terminated at about 9 Brix (1.017), so about 6%. I intended it to hit about 6.5% and 1.012 FG. But I needed a blowoff tube for that one cause it went crazy (it even popped my rubber stopper off!). I used Pale 2 row as my base malt with five different specialty malts.

It drives me nuts that they get so close and then they stop!

 

[BrewnWKopperKat]

I brew 1 gallon batches and use the standard 1 gallon glass carboys.

Have you considered fermenting in a (slightly) larger container?

 

[Phoenix1854]

So, examining this a bit... I assume the batches you are using blow off tubes with tend to be higher gravity worts. Is that the case? If so, do your higher gravity batches happen to have grain bills that contain a higher proportion of specialty malts? Do your blowoff batches use different yeast strains than your non-blowoff batches? And, where are your expectations for final gravities coming from?

Anything with an OG of 1.060 or greater tends to need a blowoff tube. That has been most of my beers. I brewed a amber ale and session IPA that had OGs of 1.055 and 1.046, and both hit their intended FG and did not require a blowoff tube.

I generally alternate back and forth between extract and all grain, but regardless of the type, the result is still the same when using the blowoff tube. I have brewed many more extracts than all grain up to this point, but am moving forward with more all grain batches. But I generally like more complex beers, so the recipes I have created tend to use a variety of specialty grains.

As for yeast, it does not seem to matter what I use. My last all grain batch I used liquid instead of dry (WLP001) and had the same result as I normally do using dry yeast with a blowoff. My expectations generally come from calculators on Brewer's Friend.

 

[Phoenix1854]

Have you considered fermenting in a (slightly) larger container?

I have considered it. Would too much headspace negatively impact the beer?

 

[cactusgarrett]

One thing you could do is sacrifice a little bit of the batch to run a fast ferment test side-by-side with the fermentation: once fermentation is visibly active, pull a bit to a small taster glass. Having a stir plate would be ideal, as then you'd stir that small sample for a couple days, even with a bit of heat. This should drive this sample down to the lowest gravity your beer potentially has, so you know what the endpoint of the main batch should be. That way you know if the beer is done, or if something caused fermentation to stall.

 

[Phoenix1854]

Agreed to the above and want to add - refractometer - not good for measurements w/ alcohol in them. Not without conversion work at a minimum. I use a hydrometer myself, the refractometer gets put away once I pitch yeast.

I use Sean Terrill's calculator to measure once alcohol is present. Since I only brew 1 gallon batches, I would rather not use a hydrometer.

 

[k-os]

I definitely pitch enough yeast and I assume that I have enough yeast left in there to finish the job. As for headspace, I usually fill hit the "One Gallon" marker on your typical 1 gallon glass carboy, or just below it. So I think there is enough.

I recently brewed an all grain robust porter with an OG of 16 Brix (1.063) and it terminated at about 9 Brix (1.017), so about 6%. I intended it to hit about 6.5% and 1.012 FG. But I needed a blowoff tube for that one cause it went crazy (it even popped my rubber stopper off!). I used Pale 2 row as my base malt with five different specialty malts.

It drives me nuts that they get so close and then they stop!

Is the terminal gravity of 9 Brix what you read directly from our refractometer, or after correcting for presence of alcohol?

As @tracer bullet mentioned, once alcohol is present you cannot directly take the refractometer reading. You have to adjust for the presence of that alcohol with a Correction Factor.

EDIT: Just saw your reply you posted as I was typing my original post.

Have you calculated your own correction factor, rather than using the default provided in Sean Terrill's calculator? The correction factor will change with the color (SRM) of the beer, as it will refract light differently for a dark beer than a pale beer.

 

[Phoenix1854]

Is the terminal gravity of 9 Brix what you read directly from our refractometer, or after correcting for presence of alcohol?

As @tracer bullet mentioned, once alcohol is present you cannot directly take the refractometer reading. You have to adjust for the presence of that alcohol with a Correction Factor.

EDIT: Just saw your reply you posted as I was typing my original post.

Have you calculated your own correction factor, rather than using the default provided in Sean Terrill's calculator? The correction factor will change with the color (SRM) of the beer, as it will refract light differently for a dark beer than a pale beer.

I have not actually. I usually just use the default wort correction factor (which is 1.040 on Sean's calculator). Is there a suggested method to do that? The robust porter I referenced was very dark, almost stout like.

 

[k-os]

I have not actually. I usually just use the default wort correction factor (which is 1.040 on Sean's calculator). Is there a suggested method to do that? The robust porter I referenced was very dark, almost stout like.

I use the spreadsheet that Brewer's Friend provides. I group my brews by SRM color within a certain range. Most of the beers I've brewed are on the lighter/pale end.

https://www.brewersfriend.com/how-to-determine-your-refractometers-wort-correction-factor/

 

[BrewnWKopperKat]

Would too much headspace negatively impact the beer?

What impacts are you concerned about?

 

[VikeMan]

Have you calculated your own correction factor, rather than using the default provided in Sean Terrill's calculator? The correction factor will change with the color (SRM) of the beer, as it will refract light differently for a dark beer than a pale beer.

I have never heard that wort color (per se) has any significant impact on refractometer readings. Is there a source for this? One thing that definitely does affect readings is the sugar/dextrin makeup of the wort. Each (non-sucrose) sugar/dextrin has its own index that's different from sucrose's, and that's the main reason for the wort correction factor. The fact that different worts have different sugar/dextrin profiles is what makes it tricky to select a WCF.

 

[Phoenix1854]

What impacts are you concerned about?

Primarily oxidation. Would fermenting 1 gallon batches in a 3 gallon carboy have any negative effects such as oxidation?

 

[Knightshade]

If you're worried about "too" much headspace, maybe give a "Little" Big Mouth Bubbler a look. I was using them when I was doing 1G batches and really liked them. 1.4G

 

[eric19312]

Honestly taking a bunch of gravity samples is going to result in oxidation regardless of headspace. If you care about oxidation I'd just keep on swapping the blow off tube for a regular airlock as soon as you can and then leave the beer alone another week or 10 days or so. Take a gravity sample as you are bottling and if it is much higher than expected you could add a bit of sugar to the carboy (to get some yeast activity to try to scrub oxygen you just introduced when you took the sample) and let it go another 1-2 weeks before bottling.

Likely it really was done and your actual issue is you are having difficulty getting full attenuation of higher gravity worts. More yeast, more viable yeast, oxygen, bumping temps as activity starts to slow may all be issues [worth looking into].

 

[BrewnWKopperKat]

Let's go back here where you said ...

so maybe my refractometer is off.

If you haven't calculated a Correction Factor for your specific hydrometer, it's plausible that this is factor in the problem you are seeing.

If you still see the problem with FG readings from a hydrometer or from your refractometer with the Correction Factor applied, you may want to try a slightly larger fermenter (Little BMB as suggested by @Knightshade , two gallon food grade pail, ...) as a next step.

You'll need to set aside the idea that hydrometer samples are "wasted" beer and may need to accept the probably that the beer may not store well due to oxygen ingress.

 

[Phoenix1854]

Thanks for all the great insight everyone. I think a Little BMB might be a good investment. My beers certainly do not come out bad and are actually quite good, so it could just be an issue related to readings with a $20 refractometer/wort correction factor.

 

[Phoenix1854]

Would Fermcap-S also be a potential problem solver for huge fermentations and preventing the use of a blowoff tube?

 

[VikeMan]

Would Fermcap-S also be a potential problem solver for huge fermentations and preventing the use of a blowoff tube?

Fermcap-S can be very effective. I don't use it myself, but I've seen it in action (or rather non-action) in some pretty small headspace fermentations.

 

[Phoenix1854]

Fermcap-S can be very effective. I don't use it myself, but I've seen it in action (or rather non-action) in some pretty small headspace fermentations.

Sounds promising. I may try that first to see if it is effective since it is the cheaper option.

 

[tracer bullet]

Fermcap works for sure, I used some on a Russian Imperial and it had way less krauzen than ever before.

So, I have a thought, but first one other one - Sometimes really vigorous fermentation (i.e. lots of yeast pitched) can be done in just a couple days. I don't mean 100% done, but the vast majority of fermentation can be wrapped up and your gravity might not change much after that. Not day to day anyhow.

The other thing is your final gravity. Maybe you're already there. How do you know you haven't reached it? Just because you plan to hit a gravity, or a recipe says so, or a calculator whatever else doesn't mean it'll happen. Mash temp alone can make a big difference, running low tends to get lower gravities and vice versa.

If your end results aren't overly sweet or something, and nothing seems amiss with the process, you may just be finished and that's that.

Just for kicks repeat a recipe shooting for a 10 degree mash temp difference and see what happens. Once in the high 150's, once in the high 140's. Let me find a Brulosophy experiment on this... Ok here:

http://brulosophy.com/2015/10/12/the-mash-high-vs-low-temperature-exbeeriment-results/

 

[Holden Caulfield]

Generally I am within 0.5-1% of what I am aiming for, but it never quite gets there.

Given the accuracy, calibration of the tools, and the process imperfections:

• Hydrometer calibration
• Refractometer calibration
• Temperature of beer, sample
• Accuracy and calibration of the thermometer
• Bubbles on hydrometer
• Reading below the Meniscus
• All of the above that relate to the OG measurement

Not to mention the range given for attenuation on yeasts and the imperfect science on the impact of mash temperature, PH, mash time, and types of malts on fermentability (if using extracts, same issue, you have no idea exactly what malts were used and how the were mashed, and even if you did you can only ballpark the impact).
You are doing well quite well are probably chasing windmills.

maybe it is not a problem at all.

You nailed it^

 

[Mexibilly]

Hey all, I am encountering a weird problem or maybe it is not a problem at all. I brew 1 gallon batches and use the standard 1 gallon glass carboys. Most of my beers need a blowoff tube for the first 72 hours of fermentation when the yeast goes crazy. Once it slows down, I replace the blowoff tube with a standard airlock. The problem is, most of the actual fermentation seems to stop after that initial activity. I check the gravity periodically throughout the next week or so and it barely moves and never reaches its final gravity. On the other hand, beers that do not need a blowoff tube always reach their final gravity.

One thing I have noticed is that there is always lot of yeast that escapes through the blowoff tube and into the cup at the end of the tube. Could that be a reason I am not hitting final gravity for beers with blowoff tubes? Generally I am within 0.5-1% of what I am aiming for, but it never quite gets there. I never under pitch the yeast and each beer ferments at a constant room temperature with little fluctuation (66-69). The beer generally turns out pretty darn good regardless, so maybe my refractometer is off.

Given your description, and what I imagine is very minimal headspace, I think you probably identified the problem
Maybe try a 1.5 gal fermentation vessel, at least for primary?

 

[Phoenix1854]

Thanks to everyone who replied to this thread. Really appreciate all the great advice.

Perhaps ironically, I won third place in my first ever homebrew competition this past weekend for my coffee porter, which was one of those that required a blowoff tube and I thought had ceased fermentation prematurely.