When and How Often to Measure FG

[LargeNCharge]

I've seen conflicting advice on this one and am curious to get some advice from experienced brewers.

My understanding is that you want to open the fermenter as little as possible, and you also toss out precious liquid happiness every time you measure. So assuming I wasn't doing a secondary fermenter, when should I first open it to check FG? And how often should I measure after that before bottling? Or is it not even worth taking multiple measurements unless the FG is too high?

 

[iBrewR]

OG = Original Gravity
FG = Final Gravity
SG = Specific Gravity (both OG and FG are SG readings)

Two of the same SG readings taken 2-3 days apart means the last one was actually your FG

Don't take the first one before 10 days

Don't toss the sample. Drink it. It'll give you an idea where your beer is heading

 

[TexasDroughtBrewery]

I think 10-14 days is a good starting point before checking it the first time if its a typical ale. I usually do everything on Saturdays so the 10 day mark would be in the middle of a week for me. Anyhow two weeks and most beers are done some people say leave it for three to be sure.

How often to check after the first time... depends, if you check it the first time and its at the FG its supposed to be...I rack it. Other wise I usually leave it 3-4 more days before testing again..sometimes a week (remember the Saturday thing)

It is true you don't want to open it to many times, each time has a chance of an infection if your not careful.

 

[flyfishnevada]

Unless you are recording the results for some reason (maybe as you experiment with recipes or something), you don't have to take SG readings at all. Some brewers record all that for reference but it's not mandatory.

If you're just brewing recipe kits and you've got good fermentation, the beer is going to do what it's going to do. Leave it in the fermenter for about 3 weeks and it will finish and clear. You might want to take a FG reading when you bottle to insure it turned out right and you didn't make any mistakes but there's little you can do to fix the beer at that point. There's little you can do to "fix" the beer after the boil.

More important is that you got a good ferment. You got krausen, you got bubbles in the air lock. If that happens, you'll have beer and though it might not be perfect, it's beer.

 

[Jayhem]

Unless you are in a hurry, you will make better beer and be at FG 99.99% of the time by letting it primary ferment for 21 days before even checking it. I don't even measure FG anymore. I just let them ferment out 21 days, they are always done and ready to keg at that point. If you are in a hurry wait at least 14 days before checking to be safe. Big beers and low fermentation temps can cause some recipes to take 21 full days to finish! Belgian yeasts are like that, slow slow to finish. Typical ales using Nottingham or US05/1056 are usually done in 10-14 days.

 

[Dirt_McGirt]

I think 10-14 days is a good starting point before checking it the first time if its a typical ale. I usually do everything on Saturdays so the 10 day mark would be in the middle of a week for me. Anyhow two weeks and most beers are done some people say leave it for three to be sure.

How often to check after the first time... depends, if you check it the first time and its at the FG its supposed to be...I rack it. Other wise I usually leave it 3-4 more days before testing again..sometimes a week (remember the Saturday thing)

It is true you don't want to open it to many times, each time has a chance of an infection if your not careful.

Cosign on this. Unless it's a big beer, fermenting at low temps, or a notoriously slow finishing yeast (some belgians), it'll usually be done in 10-14 days. I typically check on day 10, then again on day 12 or 13 to be sure. If I get the same reading, I'll throw it into cold crash the next day to clear.

 

[iBrewR]

You might want to take a FG reading when you bottle to insure it turned out right and you didn't make any mistakes but there's little you can do to fix the beer at that point.

If you're bottling, you will want to take consecutive readings to be sure that gravity isn't still dropping. Not "might". Lot of reasons a beer can keep dropping even after three weeks. Especially for a new brewer. You don't want that happening in the bottle. Bottle bombs are not fun.

I don't even measure FG anymore. I just let them ferment out 21 days, they are always done and ready to keg at that point.

Could be wrong, but at four posts, really doubt he's kegging.

 

[Rockn_M]

You'll find a lot of advice here and you'll need to find out what works best for you and your setup. I typically won't check gravity until about 10-14 days. If it's a big beer or it took fermentation to start longer than I anticipated I'll wait till around 18-21 days. Once you take an initial reading wait 2-3 days then check again. If they are stable then your done. If it goes down wait a few more days before checking again.

Oh and you don't have to through out the sample...have a taste. It should taste like warm flat beer and give you a general idea of what the finished product will taste like. Although it will change when you add carbonation.

 

[blizz81]

I would suggest if you're new to brewing and / or if you want to brew a wide array of styles and types (big vs. session) beers that would likely involve using a lot of different yeast strains, that you do measure and record your FG. I'd say to always record it anyway to know where you landed vs. target for attenuation and what your ABV ended up at, but even if you don't care about those things, it will help you see how different yeasts and styles behave, especially if you get into all-grain and start playing with variables (recipe, mash temp, etc) that can greatly influence attenuation.


Repeatedly opening the fermentation vessel and taking readings will increase your exposure to oxygen, but in the grand scheme of things I'd say fairly minimally, and that the experience and savvy you gain as you start to feel your way is worth the slight bit of oxygenation you're risking. As mentioned before, there's a good chance you're bottling if you are newer to the craft, and that's going to expose you to oxygenation anyways, and there's a good chance when it comes to popping one open and drinking it, you're not going to notice it a whole lot anyways.


I agree with the rest of the advice that in general, for the majority of beer, if you give it two to three weeks in your vessel, you're likely at FG.

 

[flyfishnevada]

For the record, I'm not suggesting you shouldn't take a FG. You just don't have too. With recipe kits and strong fermentation, the recommended fermentation time is probably good to go. My point is that if you're checking to see if you've screwed something up, there's little you can do to fix it at that point.

Then again, you might want to record the specifics of that "screw up." It might be darn good beer

 

[iBrewR]

You just don't have too ....... My point is that if you're checking to see if you've screwed something up, there's little you can do to fix it at that point.

Pitch more yeast if gravity hadn't changed (dead yeast)
Swirl to resuspend if you have a stuck fermentation.
Raise temperature to help yeast finish their job.

Probably a lot more that I'm not thinking of.

The point is, yes, if you're bottling, you have to.

 

[flyfishnevada]

The point is, yes, if you're bottling, you have to.

I will agree to disagree in many cases.