How Do You Know When Your Beer, Wine, or Mead is Finished Fermenting?

If you’re brand new to brewing, you may not know when your batch is ready to bottle. Instructions given from a kit or recipe say one thing, but you’re not sure. And you shouldn’t ever bottle a batch before it’s ready! So how can you be completely sure, so that you can safely bottle your beer, mead, or wine?

Your beer, wine, or mead is finished fermenting when the specific gravity is at or near the expected final gravity and has remained stable for at least 48 hours. There is no timeframe you can reliably follow, nor any visible indicators of completion. The batch will benefit greatly if you give it more time in primary.

The second most common post I see on homebrew forums and subreddits goes something like: “The recipe and/or instructions I’m following say that my batch is ready to bottle at this time, but I think it’s still fermenting – how do I know, can I bottle it, and is it safe to let it go longer?”

(The most common question is, of course, “Is this contaminated?”)

Often, the instructions given state that the brewer should pitch yeast, give it a certain number of days, and then bottle – with no further explanation to determine if fermentation is actually completed!

Other advice might be to simply wait until the airlock stops bubbling before bottling – however long that takes.

However, neither of these statements are good advice. They’re actually quite negligent and dangerous, and can result in early bottlings and bottle bombs!

The only way to be sure that your fermentation is complete and safe for bottling is to use a hydrometer.

But I’d suggest going a step further: don’t be in a rush to finish the batch! Give it time to rest (or even age) once fermentation is complete. Not only can you be extra sure that bottling is safe when the ferment has been dormant for an extended amount of time, but your beer, mead, or wine will benefit immensely from the extra time you give it!

How NOT To Determine That Fermentation Is Complete

Brand new homebrewers are often given poor advice by others who don’t really know what they’re talking about.

The following so-called “indicators” that your batch is ready for bottling are wrong and should not be followed.

Myth #1: Fermentation Will Be Complete After a Certain Number of Days, According to Recipe

All-inclusive beer-brewing and mead-making kits designed for brand-new brewers are notorious for giving these kinds of instructions.

“Pitch your yeast, seal the fermentation vessel, wait x number of days, and it is ready for bottling.”

(The number of days could be 2, it could be 7, it could be 14!)

All-inclusive kits are notorious for giving poor advice about when to bottle the batch

Brand new brewers don’t know any better! Why would they?

So, when the fermentation is still ongoing after the designated number of days, they don’t know what to do.

(I wonder just how many didn’t go to the forums to ask if they’re doing it right and just went ahead and bottled an actively-fermenting batch….)

The thing is, every fermentation is different! There’s no way to know just how long a given ferment will take.

Their test batch might have been done at the specified time. And maybe yours will, too! But what if it’s not…?

Some ferments – the ones using Kveik yeast, for instance – will often go quicker. They can be done in a day or two!

However, I recently had a batch of ginger mead where the yeast never really got excited. It fermented just fine, but went fairly slowly and was never too vigorous. That one took multiple weeks to reach final gravity!

Myth #2: Fermentation is Complete When You Stop Seeing Bubbles in the Airlock

This one is usually advice passed on to a brand-new homebrewer from someone who kind of knows things, but is still probably new and inexperienced themselves.

As I’ve stated before, airlock activity is not a good indicator of whether fermentation is or isn’t happening.

Just because you don't see activity in the airlock doesn't mean fermentation isn't happening inside the vessel. — Just because you don’t see activity in the airlock doesn’t mean fermentation isn’t happening inside the vessel.

It’s nice to see it bubbling along early on, because that will let you know that it’s started – but just because it’s not bubbling doesn’t mean it’s not fermenting!

Sometimes, the yeast works aggressively at the start, and the airlock bubbles away rapidly – and then it dies off as the yeast slows down. Yet, they’re still in there, chewing on the last few bits of sugar… just not as vigorously, since there’s not as much sugar left.

Other times, they never really get going for whatever reason: temperature, yeast strain, etc. They chug along quietly, slowly chewing through the sugars in your wort or must, but never really making a fuss. You may never see any krausen or airlock activity for the entire fermentation – but a hydrometer reading will show you it’s still happening.

The ginger mead I brewed recently is the perfect example: the yeast worked for weeks, and the gravity readings slowly dropped from 1.060 to 0.990, but there was no activity in the airlock during that time!

(Yes, I know, it’s a pretty low O.G. for a mead: this one was to be a smaller kegged and carbonated mead!)

I would’ve never known that anything was happening if I wasn’t using a semi-transparent BrewDemon fermenter! I was able to see the liquid itself bubbling along, and eventually, the yeast started flocculating and the mead clearing.

But the only way I knew it was done was when I saw the F.G. as low as it was.

How to ACTUALLY Determine When Fermentation is Complete

There is only one way to truly know when your fermentation is complete.

All that it requires is a hydrometer.

Hydrometers are nice for calculating your ABV, but even if you don’t care you should still own one so you can determine when your batch is ready for bottling.

Truth: Fermentation is Complete When the S.G. is At or Near the Expected F.G. and Remains Stable for 48 Hours

To determine when fermentation is complete and your batch is “ready for bottling” simply take periodic gravity measurements.

Once the gravity measured is within a point or so of the expected F.G., and it remains stable across multiple readings (spread out across a few days) then you can safely assume that your batch is done.

It is important that both of these things occur together!

My recent ginger mead was stable at 0.990 - that's how I knew it was done! — My recent ginger mead was stable at 0.990 – that’s how I knew it was done!

Sometimes, you might have a stalled fermentation, and the measured gravity will not move for a period of time despite fermentable sugar still being available in solution. In this case, your readings will show as “stable” but the unfermented sugar will produce a gravity higher than your expected F.G. In this case, fermentation can possibly kick-start again – you don’t want that to happen in bottles!

On the other hand, your gravity can go below your expected F.G. in very niche circumstances – like if you ended up with a wild yeast infection (or something similar) which can chew through sugars even Saccharomyces cerevisiae can’t consume!

However, you’re not likely to have both of these things happen at the same time. So, as long as you’ve hit your F.G. and the gravity is stable, you’re safe.

If you want an extra indicator to be even more sure – wait until the yeast begin to flocculate, the haze settles, and your batch starts to clear just a bit.

(Do note that yeast flocculation is not a good indicator on its own. Only use it to be extra sure, in conjunction with a stable F.G.)

What Is Your Expected F.G.?

Knowing your expected F.G. is simple: for nearly all meads, wines, ciders, etc. where the recipe does not include fermentable sugars, the yeast will happily chew through all of it and produce a dry product below 1.000.

For beer (and anything else that includes unfermentable sugar) you can simply plug your recipe into something like Brewer’s Friend or the BrewFather app to determine what your expected F.G. will be.

The Real Answer: Be Patient, Let Your Batch Rest and Age

I said “ready for bottling” in quotes above because it’s honestly not a great idea to bottle the moment your batch has finished fermenting.

I never bottle or keg a batch as soon as fermentation is complete. I honestly don’t know the last time I’ve done so.

Just about every batch will benefit immensely from, at the very least, a short rest – and usually a lengthy aging period.

For those of us who have been doing this a while, it almost goes without saying for meads and wines. Many meads and wines are barely acceptable immediately after fermentation, and you’ll likely want to give them at least a few months – maybe even a year or more – to age and let the flavors mellow, meld, and improve with time.

What might surprise some is that beer will benefit from a short rest period after fermentation is done, as well! Months or years is usually unnecessary (and not desirable) but a few extra weeks in the primary fermenter will give the yeast time to clean up any off-flavors and bad compounds produced during fermentation – not to mention settling out and letting the beer clarify!

If you give your beer, mead or wine time to become the best version of itself it can be, you never need to ask yourself, “is fermentation done?”

It will have been done for a while already.

Conclusion

You should NEVER bottle a batch of beer, mead, or wine before fermentation is complete.

And just because a certain, arbitrary number of days has passed, or the airlock has stopped bubbling, it does not mean that it’s ready.

If you ever find a kit or a recipe that tells you otherwise – avoid it!

The ONLY way to be sure is to measure with a hydrometer.

But as for me, I’ll keep letting my batches rest and age to perfection. As a bonus, I’ll never need to worry about whether they’re safe for bottling!