Questioning the practice of checking FG twice to determine if FG has been achieved

[Holden Caulfield]

As home brewing evolves, many past practices for making great beer have been re-evaluated. For example, the need to use a secondary fermentor.

Recently, I read a post from a beginner brewer who was following instruction from his LHBS to check his gravity after a period of time, then check it again 3 days later to confirm no change in FG. This practice exposes their beer to possible infection as well as exposes their beer to a big gulp of oxygen for a minimum of three days. Neither of these are best practices for making good beer. I would like to obtain other home brewer's thoughts on this?

After 50+ batches of all grain beer, I have never once checked to see if FG has been hit. My process is to check the internet on what to expect from my yeast and then wait until my airlock basically stops bubbling and then give it a few days to clean up. I do some quick back of the envelop calculations on what could possibly be left by estimating the number of average bubbles per minute over the growth and stationary phase and then calculate how many days fermentation would have to continue to impact FG. For example, if a lager bubbles once every 4 seconds for 10 days and then slows to 1 bubble every 30 seconds, and then is raised to 65 degrees for a 4 day diacetyl rest and then bubbles once every 3 mins, every day after it is only fermenting like .2% more. That said it would need to go on like this for more than 3 days just to impact gravity by 1 point. BTW, this example is much more in depth than what I usually do.

In my opinion, a better practice would be...

1. Base minimum time to leave beer in primary is 10 days
2. Leave beer in primary 3 days after bubbling slows to once every 3 minutes
3. Before packaging, check FG to see if it is in the expected range
4. If FG seems high, give beer a stir, and go back to step 2

I realize that there is always a chance of overcarb and bottle bombs. But with the health of yeast these days, the probability of this is very low and the benefits of better beer far outweigh risks.

Thoughts?

 

[MrPowers]

Thoughts, just buy a Tilt. Check SG without opening the fermenter. Wait until Tilt readings stop dropping.

 

[balrog]

My thought is two weeks, but I don't chase grain-to-glass races or percentage-efficiency-gains. I'm trying my best to not care about squirrels in the bird feeders too, but the little tree rat bastages make my blood boil, and the neighbors would look askance were I to resort to explosives.

 

[Jayjay1976]

The traditional wisdom of checking the FG twice before bottling is supposed to help anxious new brewers avoid a catastrophic bottle failure. You may no longer need to bother, but that doesn't mean the practice is no longer valid for others. I'm not dismissing your point about avoidable oxidation, but that risk is far outweighed by the real hazard of bottle bombs.

Since I keg, I package as soon as I think the yeast is done and I pull a gravity sample along the way just out of habit. If I happens to be a bit too soon, I just let the keg sit at room temp for a few days before moving it into the keezer. If fermentation seems to have stalled, I strap a heating mat to the keg and raise the temp to help it finish out.

 

[Holden Caulfield]

The traditional wisdom of checking the FG twice before bottling is supposed to help anxious new brewers avoid a catastrophic bottle failure. You may no longer need to bother, but that doesn't mean the practice is no longer valid for others. I'm not dismissing your point about avoidable oxidation, but that risk is far outweighed by the real hazard of bottle bombs.

My intent on this post is not to help me. But rather to get some perspective from other brewers on what they would recommend to a new brewer. I believe what you are saying is that you would still recommend checking gravity twice as the risk of bottle bombs outweigh the benefits of better beer, at least for new brewers.

 

[Broothru]

My intent on this post is not to help me. But rather to get some perspective from other brewers on what they would recommend to a new brewer. I believe what you are saying is that you would still recommend checking gravity twice as the risk of bottle bombs outweigh the benefits of better beer, at least for new brewers.

What JayJay said^^^^

Ten or 12 years ago, a friend from work (highly educated, family roots in the Czech Republic) decided to do a brew-on-premises intro course at the LHBS. For newbies they were advising a simple one-stage fermentation of about three weeks, undisturbed, in their cold room, after which you'd come back for a bottling session. I lectured him for about a month on how you had to do a racking after no more than one week of 'primary' and take frequent gravity readings or else your beer would be crap. Boy was I wrong.

Guess what I do now? Yep. Seal up the fermenter and do a one-stage "primary/secondary" that takes about three weeks. Of course I now also ferment in an SS conical with temperature control, do trub dumps and harvest yeast, and draw 2-3 ml samples occasionally to measure gravity with a refractometer. The beer turns out pretty good, so I'm told.

 

[BrewnWKopperKat]

I believe what you are saying is that you would still recommend checking gravity twice as the risk of bottle bombs outweigh the benefits of better beer, at least for new brewers.

One wants to know that fermentation has completed and FG is within the anticipated range for the recipe.

A picture is worth a thousand words --

 

[NGD]

I asked myself this same question while reading “How to Brew” prior to making my first batch. The answer I settled on is pretty much what Jay stated. When I was newer I checked gravity twice. Had a few beers get stale because of it. Now its 2-3 weeks and package with an FG check prior to make sure I’m close to est. FG. I’ve also had my bacon saved by testing multiple times at least once. Had a large beer not ferment out as completed, but was in 3 points of estimated. Wanted to carb close to limit of the bottle but waited a bit. Ended up shooting past estimated FG by 3 points. Had I bottled prior I would have had a huge mess and possible injuries.

I don’t think it would take many reports of harm to person or property before someone of a litigious nature in government decided home brewing was to dangerous for the layman and people should either be licensed or prohibited from homebrewing.

 

[BrewnWKopperKat]

This practice exposes their beer to possible infection as well as exposes their beer to a big gulp of oxygen for a minimum of three days. Neither of these are best practices for making good beer.

Home brewing forums talk a lot about the risks of infection and oxygen ingress without measuring that risk.

I suspect that with good sanitation practices, the risk of infection is effectively zero.

I also suspect that with good transfer practices, the risk of oxygen ingress approaches zero.

But without measurements, it's hard to know for certain.

In my opinion, a better practice would be...

1. Base minimum time to leave beer in primary is 10 days
2. Leave beer in primary 3 days after bubbling slows to once every 3 minutes
3. Before packaging, check FG to see if it is in the expected range
4. If FG seems high, give beer a stir, and go back to step 2

I realize that there is always a chance of overcarb and bottle bombs. But with the health of yeast these days, the probability of this is very low and the benefits of better beer far outweigh risks.

Thoughts?

With regard to bubbles:

Bubbles do not equal fermentation.

A single FG reading is not enough to know that FG is stable.

In some cases, one may choose to avoid "low probability events" as the consequences are not desirable.

There is a way to take FG measurements without introducing oxygen (Tilt, et al).

Is there an inexpensive way to take FG measurements (for hydrometers or refractometers) that does not expose the beer to oxygen ingress?

 

[eric19312]

Recently, I read a post from a beginner brewer who was following instruction from his LHBS to check his gravity after a period of time, then check it again 3 days later to confirm no change in FG. This practice exposes their beer to possible infection as well as exposes their beer to a big gulp of oxygen for a minimum of three days. Neither of these are best practices for making good beer. I would like to obtain other home brewer's thoughts on this?

I also cringe when I see this advice for same concerns you raised. Over time I moved from testing hydrometer samples to make sure it was ready to visual cues...airlock bubbling and yeast dropping, then just got comfortable that I'd never seen a single batch of ale take 3 weeks to finish. When I switched to kegging I revised that to two weeks and like @Jayjay1976 mentioned if the gravity seemed a bit high at kegging leave the keg sealed up at room temp a few days before chilling.

But...I brew in a pretty narrow range these days. Last batch I brewed over 1.059 was in 2018. Only 3 of the 29 batches I brewed since then used yeast other than US-05. On quite a few batches I do use a Tilt...not to know when to package but to know when to start diacetyl rest and tell me when to crash the yeast and get on with dry hopping. None of the batches I used the Tilt on took more than 1 week to reach terminal gravity. So I know my yeast and my beer pretty well. But I can really empathise with the LHBS owner giving advice to new brewers. Maybe the guy made some 1.120 barley wine and pitched pretty old smack pack into it but can't remember for sure how old it was or if was ale or lager yeast when he calls you on the phone...but the airlock stopped bubbling and he is just super eager to get this sure to be award winning beer into bottles in time for his cousin's wedding. No I get it.

 

[Qhrumphf]

Sampling port and positive pressure to negate vacuum. Problem solved.

Play with STA1+ yeasts and you'll find out quickly that even stable over 3 days doesn't always mean much.

If you don't want to do multiple samples, do a forced fermentation test. You can then compare actual to expected.

 

[passedpawn]

As home brewing evolves, many past practices for making great beer have been re-evaluated. For example, the need to use a secondary fermentor.

Recently, I read a post from a beginner brewer who was following instruction from his LHBS to check his gravity after a period of time, then check it again 3 days later to confirm no change in FG. This practice exposes their beer to possible infection as well as exposes their beer to a big gulp of oxygen for a minimum of three days. Neither of these are best practices for making good beer. I would like to obtain other home brewer's thoughts on this?

After 50+ batches of all grain beer, I have never once checked to see if FG has been hit. My process is to check the internet on what to expect from my yeast and then wait until my airlock basically stops bubbling and then give it a few days to clean up. I do some quick back of the envelop calculations on what could possibly be left by estimating the number of average bubbles per minute over the growth and stationary phase and then calculate how many days fermentation would have to continue to impact FG. For example, if a lager bubbles once every 4 seconds for 10 days and then slows to 1 bubble every 30 seconds, and then is raised to 65 degrees for a 4 day diacetyl rest and then bubbles once every 3 mins, every day after it is only fermenting like .2% more. That said it would need to go on like this for more than 3 days just to impact gravity by 1 point. BTW, this example is much more in depth than what I usually do.

In my opinion, a better practice would be...

1. Base minimum time to leave beer in primary is 10 days
2. Leave beer in primary 3 days after bubbling slows to once every 3 minutes
3. Before packaging, check FG to see if it is in the expected range
4. If FG seems high, give beer a stir, and go back to step 2

I realize that there is always a chance of overcarb and bottle bombs. But with the health of yeast these days, the probability of this is very low and the benefits of better beer far outweigh risks.

Thoughts?

^^ that's what I do. I never open fermentor. Maybe I did back in my noob years, but it's been like clockwork for so long. Ales 2 weeks fermentation, lagers 3 weeks. It's ALWAYS done.

I always check gravity when brewing, then transferring to keg because I keep records of my brews.

(salinger fan?)

 

[Sammy86]

Leave beer in primary 3 days after bubbling slows to once every 3 minutes

Considering bubbling air locks have been proven to not be indicators of fermentation I would be very careful telling new brewers to use that as a sign that fermentation is complete.

As is stated above 14-21 days the yeast have done their job...even the big boys of brewing check their FG before transferring to bright tanks and or packaging.

 

[SFC Rudy]

When you bake a cake do you take it out 15 minutes early and taste it?

Be patient. Wait two weeks. If you have to go buy some beer to drink in the mean time, it'll give you more bottles to fill with future batches.

 

[Holden Caulfield]

Considering bubbling air locks have been proven to not be indicators of fermentation I would be very careful telling new brewers to use that as a sign that fermentation is complete..

Proven by whom?

The formula for beer fermentation is C6H12O6 → 2 C2H5OH + 2 CO2.

If the fermentor is sealed properly (which would be indicated by the bubbling during the growth and stationary phases), then fermentation has stopped. Some clean up of byproduct chemicals may take place, but if there are no bubbles, then C02 is not being produced.

I understand the concerns over a beginner packaging a stuck fermentation beer or a beer where the airlock never bubbled (fermentor not sealed). But a reasonableness confirmation of FG by hyrdrometer just before bottling, 3-5 days after bubbling has ceased, should be safe.

I wonder what is the most frequent cause of exploding bottles - packaging too soon, or too much priming sugar?

 

[Broothru]

Proven by whom?

The formula for beer fermentation is C6H12O6 → 2 C2H5OH + 2 CO2.

Yeah, but maltose is C12H22O11

 

[VikeMan]

Sampling port and positive pressure to negate vacuum. Problem solved.

Yep. To mis-quote Dutch Dooley, taking a sample is about as worrisome as a cloudy day.

 

[VikeMan]

Yeah, but maltose is C12H22O11

Oh, crap. How can I keep maltose out of my wort?

 

[RM-MN]

If the fermentor is sealed properly (which would be indicated by the bubbling during the growth and stationary phases),

During the early fast part of the fermentation so much CO2 is produced that it can overwhelm a slight leak. As fermentation slows that slight leak can now take CO2 away from the airlock and it stops bubbling. If we keep the idea that the airlock is simply a device to allow excess CO2 to escape and entertain the brewer while doing so and train them that the only true indicator of the end of fermentation is the hydrometer we will have educated them.

I will use software to determine the expected FG and I may take only one reading if the hydrometer sample is very close to that and I know I have allowed enough time for fermentation to have completed. If the hydrometer reading is substantially different from the expected FG, I will take another reading before bottling for my safety.

 

[Broothru]

Oh, crap. How can I keep maltose out of my wort?

Well... first you get some really good yeast.....

 

[Dland]

Since I started spunding, I do a gravity check w trub dump when fermentation has slowed. If it is within .006-10 of expected FG, I rack to kegs and let the rest work off while achieving free and O2 free carbonation. If a lager, do the D rest at this time as well.

As stated by someone else, knowing for sure beer is finished working is much more important when bottling.

 

[thehaze]

When I started brewing, I did check gravity twice. just to make sure. Once I had brewed 30-40 batches, I had an idea when a beer was done taking into consideration factors like grainbill, yeast, OG, adjuncts, etc. I have been taking gravity samples since. I do however check final gravity when I bottle and or keg.

 

[mashpaddled]

I tend not to check gravity at the end of fermentation once, let alone twice, because like a lot of other responses I anticipate that after 2-3 weeks fermentation is complete or it is a beer I intend to age for a longer period (high gravity, sour, brett) in which case I know fermentation will end long before I think about packaging the beer.

That said, there are good reasons to check FG and check more than once. Working on a short timeline, trying to perfect a recipe, etc. It is best practice to collect the data in the event you need to troubleshoot the batch or recipe and IMO a good practice for new brewers to develop and then decide whether they need to keep doing it consistently.

 

[TheMadKing]

I'll chime in with a few points

• Not checking your final gravity is a good way to make sure you have incomplete records and don't make consistent beers
• The only way to be SURE that fermentation has finished is to take at least 2 gravity readings. 1 reading is a datapoint, 2 readings is a trend. New brewers need simple advice, not nuanced advice, and this is the safest way for bottlers to make sure they aren't making grenades
• Opening a bucket style fermenter and taking a gravity sample with a syringe is indeed a good way to introduce oxygen, which means that new brewers should be steered toward fermenters with sample/transfer ports, this will reduce the oxygen slightly unless they use a CO2 filled balloon or cask breather to backfill the fermenter while taking a sample.

Here's where I go off the rails - if you keg beers, it's somewhat irrelevant to the quality and safety of the final product whether fermentation is truly complete or not. Some beer styles IMO (british ales and some lagers) see a flavor benefit from cold crashing before primary fermentation is technically "complete".

I usually will keg my beers after about 7 days for most american ale styles, 5 days for most british ale styles, and 10-24 days for STA1+ and lagers. At kegging I'll take a gravity and taste sample. If its a diacetyl bomb or the FG is suspiciously high I'll just spund it in the keg for a few days. If it tastes more or less finished and the FG is +/- 5pts I'll start the cold conditioning process.

Complete metabolism of available sugars ≠ the optimal flavor profile in all cases

 

[NGD]

@RM-MN beat me to it. Until I upgraded to a speidel, 2 of the 3 buckets I use have leaks small enough that it appears as if fermentation stopped much earlier than anticipated. I’d much rather direct a new brewer to do something that may oxidize their beer vs. potentially produce bottle bombs. Their experience and technique will improve with time.

Experienced brewers will do whatever the hell they want anyway.

 

[bleme]

Proven by whom?

The formula for beer fermentation is C6H12O6 → 2 C2H5OH + 2 CO2.

If the fermentor is sealed properly (which would be indicated by the bubbling during the growth and stationary phases), then fermentation has stopped. Some clean up of byproduct chemicals may take place, but if there are no bubbles, then C02 is not being produced.

Bubbles don't mean CO2 is or is not being produced. Bubbles means that pressure inside the fermentor is higher than pressure outside. If you have a high pressure system move in, bubbles may stop but that doesn't mean it isn't still fermenting.

 

[AzOr]

Yeah I don’t take fg readings on most of my batches either.

But, But newer brewers may want to think about the type of yeast they are using. There are some strains w a reputation of conking out prematurely, only to start again under diff conditions. This could lead to bottle bombs.

If it’s a standard ale yeast, the above mentioned shortcuts may be ok.

 

[Broothru]

Since I started spunding, I do a gravity check w trub dump when fermentation has slowed. If it is within .006-10 of expected FG, I rack to kegs and let the rest work off while achieving free and O2 free carbonation. If a lager, do the D rest at this time as well.

As stated by someone else, knowing for sure beer is finished working is much more important when bottling.

Curious about your exact process, as I'm thinking about trying a similar approach. The way you described it is the way I'd intended to do it when I first got an SS conical. My intent was to ferment in the conical down to ~5 pts of FG, transfer to keg and spund. It worked OK except for the large amount of settled trub and yeast after conditioning/lagering was complete. I was wasting 2-3 liters in every batch. So I got a unitank. I love the flexibility of not having to worry about pressure > 2 psi, as well as the "ferment, dump trub, spund, harvest yeast, crash, keg" cycle of workflow. By the time it gets kegged, the beer is already carb'd (for free) and is at serving temperature. And I'm getting 5+ gallons of clear beer with no crud in the first half-dozen glasses.

The SS conical doesn't get as much work as the unitank, so I could increase my thru-put if I transferred to a keg for spunding (x2 fermenters = 2x beers). Do you dump trub early in the fermentation? I've been thinking that if I chill to say 50F for a day or so after transferring from the BV into the fermenter that I could get most of the hot and cold break to settle into the cone and get dumped. That is to say, chill to 50F, dump trub, then pitch yeast and oxygenate to start fermentation. Five points before FG, transfer to a keg and spund while allowing the temperature to free rise to ambient (around 68-70F 'ish') to allow the yeasties to finish and clean up their messes. There would still be some residual yeast as well as the fine lees that would collect at the bottom of the keg, but not nearly as much as kegging immediately 4-6 days after brew day.

I've been wanting to try this with a split batch fermentation between the conical and the unitank into two 2.5 gallon kegs. Half the batch would ferment and spund in the unitank while the other would get transferred to the keg for spunding. Unfortunately I'm limited by the size of my BV and can barely get 5 gallons for a batch size unless I dilute with water post-boil. Plus, the chiller coils would only be less than half submerged into the fermenting wort. Curious about your process and how much you loose out of a 5 gallon keg to cloudy pours.

 

[Broothru]

Complete metabolism of available sugars ≠ the optimal flavor profile in all cases

Very true. ^^^

 

[Holden Caulfield]

Bubbles don't mean CO2 is or is not being produced. Bubbles means that pressure inside the fermentor is higher than pressure outside. If you have a high pressure system move in, bubbles may stop but that doesn't mean it isn't still fermenting.

Agreed.

However the new home brewer will probably be using a simple S or 3 piece airlock so the system will not be under pressure. If it is under pressure, then the airlock is blocked in which case they will experience either a blow out of the airlock, if using a carboy a blowout of it, or a big foam over when they open the fermentor. No matter the case, the homebrewer will need to clean up the mess, close up their fermentor, put the airlock back on, and wait for the all bubbling to cease. Finally, after 3-5 days after all bubbling ceases, prior to packaging they can confirm that the Krausen has fallen, the beer has cleared, and the final gravity is in the range of what is expected prior to bottling. If FG is not in the ball park then they should rouse the yeast, close up the fermentor and follow the process of waiting 3-5 days after no new bubbles in airlock.

Just thinking about another scenario...if the fermentation is stuck, then the home brewer will still believe FG has been achieved after the two samples and they will bottle, so the outcome is the same whether they check once or twice. Only way to address this scenario is to tell home brewers to rouse their yeast every time after taking first gravity reading. Just another step exposing their beer to infection and oxygen.