Taking gravity readings without compromising your brew

I've bottled too soon, for about the second or third time now. It's no biggie, since I use PET bottles for this very reason. I can check the pressure and release it when it gets too high. Yes, it's tedious doing bottle by bottle, but otherwise it's harmless.

As you can tell, I didn't check take successive gravity readings before deciding my brew was finished fermenting. I just waited until I saw no bubbles on the surface and airlock activity stopped (in fact, it was about to start going backward).

I seem to be developing a bit of a weakness in the latter stages of a fermentation, and don't really know how to overcome it. I know that the only sure way to determine whether a ferment is done is by taking successive gravity readings. But I'm scared of opening the fermentation vessel and worse, allowing outside air in through the airlock when the spigot is open.

I know why I'm getting paranoid about this. The only brew I ever dumped got mold in it, due to me opening the fermenter to check gravity readings.

How do others manage this? There must be a simple way to get around the risk of infection?

Sounds like you need to relax and have a homebrew and stop worrying.
I've stopped using buckets (except for wine) and have switched to carboys for all my beer and cider. To pull a sample, simply pull the stopper with airlock out, put it in a small dish of star-san, then use a sanitized wine thief to get your sample. Put the stopper back in and your done. Sure, you've exposed the beer to the air but that's pretty minimal, but its better than bottling too soon.

Personally I like to pitch high, and get a really good fermentation happening. If the airlock is going nuts for a few days I just don't feel compelled to check the gravity all the time and life is good. All going to plan, I check the gravity a few days prior to bottling day and again on bottling day to confirm and that's it.

I have no problem taking gravity readings. I have a bucket of Star San. I throw my turkey baster (which I only use for brewing stuff) in there. Let it sit in the bucket for a few minutes, open the lid of my bucket, take out enough beer from the bucket to extract a sample, then use a spray bottle of Star San to spray the bottom of the lid of my primary. I then put the lid back on and take a reading, checking its gravity, color, clarity and aroma. It's worked for me for two and a half years.

If you're really conserned, you could wait longer before you bottle. How long are you letting the beers ferment before you bottle them?

When I used carboys I used a 1000 cc syring with a piece of ss tubing that I could slide into the bung hole (�&#56834. A small sample and a refractometer is all you need to determine if fermenting is done.

Here's what I do to get a sample:
I use a 35 or 60 cc syringe and some tubing that I snake down the airlock hole. Everything starsaned 1st, of course. The only problem is that the starsan degrades the rubber of the syringe plunger after a while, so they last only about 10-12 batches.
I usually make my 1st check after 2 weeks or so, and if it's at or close to predicted FG, then my 2nd is at bottling time- usually a week later.

eadavis80 said:

I have no problem taking gravity readings. I have a bucket of Star San. I throw my turkey baster (which I only use for brewing stuff) in there. Let it sit in the bucket for a few minutes, open the lid of my bucket, take out enough beer from the bucket to extract a sample, then use a spray bottle of Star San to spray the bottom of the lid of my primary. I then put the lid back on and take a reading, checking its gravity, color, clarity and aroma. It's worked for me for two and a half years.

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This is exactly what I do...haven't had any problems in three years of brewing 8 batches a year!

The concern about removing a bucket lid is less about sanitation than it is about post fermentation oxidation.

Your beer is sitting under a cap of CO2 that is heavier than air. Opening a lid slowly and carefully will not disturb that cap. And if it is not ready to bottle then it is still producing CO2 to replace what little air may have gotten in.

MaryB said:

Your beer is sitting under a cap of CO2 that is heavier than air. Opening a lid slowly and carefully will not disturb that cap. And if it is not ready to bottle then it is still producing CO2 to replace what little air may have gotten in.

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That's not how gases work. Even without temperature differences and drafts from opening the lid the gases will diffuse very quickly. If CO2 stayed under air you would be dead from sitting on the planet surface.

jddevinn said:

That's not how gases work. Even without temperature differences and drafts from opening the lid the gases will diffuse very quickly. If CO2 stayed under air you would be dead from sitting on the planet surface.

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Your main point is correct, but the claim that I so often see about "you'd be dead because CO2 would sink to ground level" isn't exactly true. Winds throughout all levels of the atmosphere would help mix the gases, so there wouldn't be a blanket of pure CO2 at the surface.

Doesn't really matter...just sayin'.

Make sure to raise the fermentation temperatures toward the end of fermentation. This will keep the yeast in suspension longer and get more attenuation.

jddevinn said:

When I used carboys I used a 1000 cc syring with a piece of ss tubing that I could slide into the bung hole (�&#65533. A small sample and a refractometer is all you need to determine if fermenting is done.

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I use a 500cc syringe. Where did you find the 1000cc if I may ask.

Something I'm going to do at some point is use a 2-hole stopper; in one hole will be the airlock, in the other I'll drop a sanitized tube down well into the beer. I'll cap the tube, but when the time comes to take a sample, I can pull it from that tube without removing the lid at all.

You could, if oxidation was a concern, feed low-pressure CO2 through the airlock. I actually do that when I rack to a keg:

I filled my keg with CO2 first by starsan displacement and then fed the gas out back into the fermentor and created a closed loop system using gravity. of course I got a little air when I inserted the autosiphon. I pack a starsan soaked paper towel around the fermentor inlet also.

PlexVector said:

I filled my keg with CO2 first by starsan displacement and then fed the gas out back into the fermentor and created a closed loop system using gravity. of course I got a little air when I inserted the autosiphon. I pack a starsan soaked paper towel around the fermentor inlet also.

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That's.....brilliant! Outgoing pressure balances incoming pressure. I'm going to do this.

mongoose33 said:

That's.....brilliant! Outgoing pressure balances incoming pressure. I'm going to do this.

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Thanks. Since you have a spigot you can purge your gas-out line with residual keg pressure just before connecting it to the top of the fermentor. Completely closed gravity fed system.

Brew_G said:

Your main point is correct, but the claim that I so often see about "you'd be dead because CO2 would sink to ground level" isn't exactly true. Winds throughout all levels of the atmosphere would help mix the gases, so there wouldn't be a blanket of pure CO2 at the surface.

Doesn't really matter...just sayin'.

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Still not how gases work. They diffuse there is no separation of different molecular weight gases independent of external mixing

Brew_G said:

Your main point is correct, but the claim that I so often see about "you'd be dead because CO2 would sink to ground level" isn't exactly true. Winds throughout all levels of the atmosphere would help mix the gases, so there wouldn't be a blanket of pure CO2 at the surface.

Doesn't really matter...just sayin'.

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Still not how gases work. They diffuse there is no separation of different molecular weight gases independent of external mixing

PlexVector said:

I use a 500cc syringe. Where did you find the 1000cc if I may ask.

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Amazon. I'm on mobile now in Germany but will link when i get home.

Is your beer sitting in the sun where surface temps heat and cause gas mixing? Exposed to winds? No? The CONFINES of a bucket eliminate that, the co2 WILL sit there.

jddevinn said:

That's not how gases work. Even without temperature differences and drafts from opening the lid the gases will diffuse very quickly. If CO2 stayed under air you would be dead from sitting on the planet surface.

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Another partial truth, in an open system yes OVER TIME. Opening a fermenter for 2 minutes is not enough time for diffusion to take place. I have seen gasses stratify on farms, and have had to rescue people who refused to wear a respirator when entering a manure pit. That pit is well ventilated yet toxic heavier than air gasses still accumulate. Same thing happens in ship and barge bilges and ballast tanks where I have seen toxic levels of gasses settle in low spots and set off the alarm on my harness. This was after opening the bilge or ballast and ventilating with a fan system.

jddevinn said:

Still not how gases work. They diffuse there is no separation of different molecular weight gases independent of external mixing

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MaryB said:

Is your beer sitting in the sun where surface temps heat and cause gas mixing? Exposed to winds? No? The CONFINES of a bucket eliminate that, the co2 WILL sit there.

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Gas diffusion does not require heat (although higher enthalpy gases will diffuse faster) or wind. This is basic physics.

MaryB said:

Another partial truth, in an open system yes OVER TIME. Opening a fermenter for 2 minutes is not enough time for diffusion to take place. I have seen gasses stratify on farms, and have had to rescue people who refused to wear a respirator when entering a manure pit. That pit is well ventilated yet toxic heavier than air gasses still accumulate. Same thing happens in ship and barge bilges and ballast tanks where I have seen toxic levels of gasses settle in low spots and set off the alarm on my harness. This was after opening the bilge or ballast and ventilating with a fan system.

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No closed or open system gas will diffuse. Concentration for humans to wear PPE is very low. A manure pit is an active souce of CO2, replacing what has been moved away ( similar to a very active fermentation)

This video has been posted on HBT several times. It doesn't quantify how much mixing there is in a given amount of time, but it demonstrates the principle:

[ame]https://www.youtube.com/watch?v=_oLPBnhOCjM[/ame]

Awesome video, really cool to be able to visualize the diffusion like that.

"after half an hour" is the key. It takes me 2 minutes to pull a sample form a fermenter and close the lid. Diffusion takes TIME to do enough to be a worry at out brewing level. And you have an active ferment going on still adding more co2 as some diffuses so it offsets. It is NOT an issue on the scale we work at unless you are in he habit of leaving the lid off your fermenter for 30 minutes...

I give the beer extra time to complete fermentation, so I almost never take gravity measurements until I'm ready to bottle. No need to worry about CO2 blankets, oxidation, or infection due to measurements.

MaryB said:

"after half an hour" is the key. It takes me 2 minutes to pull a sample form a fermenter and close the lid. Diffusion takes TIME to do enough to be a worry at out brewing level. And you have an active ferment going on still adding more co2 as some diffuses so it offsets. It is NOT an issue on the scale we work at unless you are in he habit of leaving the lid off your fermenter for 30 minutes...

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Well maybe the people worried about oxidation aren't at the same level of brewing as you then.

I've never worried about the air contaminating my beer when I take a sample. I'm more worried about what's been growing on my equipment for the past week or two than I am the air. Proper sanitization. I've never had an infected beer from the air after I've pitched yeast.

DurtyChemist said:

I've never worried about the air contaminating my beer when I take a sample. I'm more worried about what's been growing on my equipment for the past week or two than I am the air. Proper sanitization. I've never had an infected beer from the air after I've pitched yeast.

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I wonder if the "danger" from airborne nasties contaminating our beer is related to where we live, and the time of year. I suspect in Nevada it's pretty dry and I'm thinking there might not be as many such threats. Compare to, say, Florida where stuff is growing at high humidity for most of the year--or the deep south.

I'm in Wisconsin so I wasn't quite as concerned during Jan-Mar when I brewed--nothing's growing! But once I hit the summer months, I'm very careful to cover my wort post-boil so little can settle in there.

Don't know if there's a study somewhere that discusses airborne yeast by region by time of year.

Concern with air is not primarily contamination but oxidation.

mongoose33 said:

I wonder if the "danger" from airborne nasties contaminating our beer is related to where we live, and the time of year. I suspect in Nevada it's pretty dry and I'm thinking there might not be as many such threats. Compare to, say, Florida where stuff is growing at high humidity for most of the year--or the deep south.

I'm in Wisconsin so I wasn't quite as concerned during Jan-Mar when I brewed--nothing's growing! But once I hit the summer months, I'm very careful to cover my wort post-boil so little can settle in there.

Don't know if there's a study somewhere that discusses airborne yeast by region by time of year.

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Possibly however I'd be willing to be there is just as much nasty stuff in our air than yours since 50-60% of yours is water and 20% of ours is water. Combined with 30-40F temperature swings it might be interesting to see what lives in desert air vs ocean air.

I also kept my brewing inside so I assume my air conditioning filter kept out as much as was safe to breath.

MaryB said:

"after half an hour" is the key. It takes me 2 minutes to pull a sample form a fermenter and close the lid. Diffusion takes TIME to do enough to be a worry at out brewing level. And you have an active ferment going on still adding more co2 as some diffuses so it offsets. It is NOT an issue on the scale we work at unless you are in he habit of leaving the lid off your fermenter for 30 minutes...

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Wait that 30 min timeframe is for Br2 (a very heavy gas), not CO2... Diffusion of CO2 is much faster than 30 mins. However when the log phase is over and there is a lower production of alcohol there is also a lower production of CO2. When the air lock stops bubbling at a rapid rate and slows to ~20 bubbles a hour or 1 every 3 mins, or close to it. That is the time I check my beer. However, the CO2 will diffuse because of change in pressure also. That positive pressure build up will push CO2 out of the bucket. I think the best way is to work diligently. There is no reason to open the lid and walk away. Open the lid, pull the sample, pull the stopper/foil/lid over the vessel, drain the sample for your reading.

PlexVector said:

I filled my keg with CO2 first by starsan displacement and then fed the gas out back into the fermentor and created a closed loop system using gravity. of course I got a little air when I inserted the autosiphon. I pack a starsan soaked paper towel around the fermentor inlet also.

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I like this idea. Just a question about how it works. After you push out the starsan solution, do you leave the keg with positive pressure? I'm guessing yes. Then use the positive pressure to push the gas back to the fermentor and that in turns pushes beer into the keg?

Since gas flows with less resistance than liquid, you'd need enough positive pressure to overcome that difference to get the beer flowing, right?

Once you get the flow going, you can release the positive pressure and let gravity do its thing?

hezagenius said:

I like this idea. Just a question about how it works. After you push out the starsan solution, do you leave the keg with positive pressure? I'm guessing yes. Then use the positive pressure to push the gas back to the fermentor and that in turns pushes beer into the keg?

Since gas flows with less resistance than liquid, you'd need enough positive pressure to overcome that difference to get the beer flowing, right?

Once you get the flow going, you can release the positive pressure and let gravity do its thing?

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It's a helluva idea PlexVector had. I used it last night and it works great!

What is the order of how you connect the ends of the hoses?

hezagenius said:

What is the order of how you connect the ends of the hoses?

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Assuming there's pressure in the keg, I start by putting my finger over the end of the gas tubing; install the QD, which releases the gas. I let a little go through the tube (purging it), then connect it to the top of the fermenter. What you see up there is an S-shaped airlock where I cut the top off, leaving a piece of the airlock that just fits nicely into the end of the tubing.

That should release gas into the fementer. If there's a lot of pressure you'll pop the lid or the stopper, be aware of that.

Once the pressure's equalized, attach the liquid-side QD, connect to the siphon or in my case spigot, and let 'er rip. I didn't purge the liquid line; I may determine an order in which to do that, but if you purge the keg after filling it, and noting that initially the air in the line is a tiny, tiny amount of the gas inside the keg, I don't see it as a huge issue.

hezagenius said:

I like this idea. Just a question about how it works. After you push out the starsan solution, do you leave the keg with positive pressure? I'm guessing yes. Then use the positive pressure to push the gas back to the fermentor and that in turns pushes beer into the keg?

Since gas flows with less resistance than liquid, you'd need enough positive pressure to overcome that difference to get the beer flowing, right?

Once you get the flow going, you can release the positive pressure and let gravity do its thing?

Click to expand...

Having an autosyphon makes it not ideal,but I release most of the gas with the purge valve and the last little bit through the gas line before sticking in the top of the fermentor.

Great job @PlexVector. I've got a thread where we go through a similar racking process, and the discussion about oxidation (as @jddevinn can attest) gets pretty contentious. But it's interesting stuff:

https://www.homebrewtalk.com/showthread.php?t=575247