Best Indicators of a Healthy Fermentation

Best Indicators of a Healthy Fermentation

Ricky the Meadmaker
6 minute read

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Last week we wrote about why you'd want to have a Baseline Fermentation, and one of the biggest reasons is to know as soon as possible when something is going wrong. But what do you do if you don't have a robust data set? What if you're brand new to brewing? What are the signs that you have a healthy fermentation?

The good news is that there are a ton of indicators for fermentation health! Some of them are very reliable, with others you need to know what to expect from that particular batch, and others are a little complicated, but between them all, you can get a very good picture of what's going on.

First, though, what does healthy fermentation mean?

What is healthy fermentation?

A healthy fermentation is one that is all of the following:

  1. It is always defined by the product being fermented and will give parameters for all of the following.
  2. It goes at the proper speed.
  3. It finishes at the proper final gravity.
  4. It creates the secondary metabolites (yeast-driven flavors) that you want.
  5. Often, though not always, it will leave healthy yeast behind at the end which can be used for future batches.

Now, let's talk about a few questionable indicators that you hear about a lot.

A few tricky (and often unreliable) indicators of fermentation health.

Smell and active bubbling are really, really obvious indicators of fermentation, but they're both much more complicated than you'd assume at first glance.

A lot of budding fermentation enthusiasts (beer, kimchi, mead, kombucha - doesn't matter) have had their passion quashed by a housemate or - worse yet - a fiancé(e) who absolutely could not tolerate the off-gassing. The problem is that some fermentations have notoriously rank aromas. Lager beers are a well-known member of that family, but many ciders are, ahem, a bit farty, and that's without getting into some of the crazy fermentations like fish and game.

A particular smell can be a good sign, but only if you're very familiar with the brew (see the aforementioned article about Baseline Fermentations). A lot of sulfur can mean that you have an infection or that your EC-1118 is doing exactly what it's supposed to.

As for bubbles, they're reliable in one way: Something is happening. Something may not be what you expect, however.

This is probably a good, healthy fermentation

Back when I worked at a homebrew shop, it was amazing the number of people who never saw a bubble, and were just about to throw away their batch when they tasted it or, better yet, took a gravity reading and found that it was DONE! How is that possible? They didn't seal the bucket lid properly, and all of the CO2 escaped around the edge instead of up the bubble lock!

On one terrifying occasion, the same thing even happened at our meadery: we had failed to seal the hop port correctly and nearly all of the CO2 for the first two days made it out of the air gap.

On the other hand, many brewers panic if they don't see a bubble for 24 hours after pitching. While this is often a bad sign (maybe the wort wasn't cool enough, maybe the yeast isn't viable) there are plenty of brews that have a substantial lag phase - on very rare occasions as much as 72 hours - and then take off like a shot.

Then there's the other end of the spectrum: days of bubbling with no gravity change. This almost always happens at the end of a fermentation and is caused by off-gassing (technically, outgassing, but it's confusingly also called off-gassing in this case). That's simply the dissolved CO2 finding its place at home with its kin up in the atmosphere. Plenty of bubbles, but no fermentation.

Good indicators of fermentation health.

Well, might as well start off with bubbling since we just finished with it! Good, rapid bubbling (especially with an aroma you expect) is a pretty solid sign that your fermentation is going apace, and a cessation of bubbling is a good idea that the fermentation is done.

No more bubbles for several days paired with a final gravity reading in line with what you expect is a really good indicator that your fermentation hit at least a few of its marks.

The next indicator is the proxy that we use at Groennfell Meadery: temperature cycling.

Watching how often our chiller needs to kick on is a great way to see how active the yeast is. It should cycle slowly, then faster and faster, then slowing down to a flatline. This pattern tells you that the yeast is doing what it's supposed to and at the right pace. If the cycling gets slow way before you're at final gravity, you're looking at a potential stall.

Temperature Cycling in a Healthy Fermentation

That big drop there is a late cold water addition. As usual, all graphs come from our BrewMonitor which we can't recommend highly enough for all pro brewers.

Daily gravity readings with a ski-slope drop are an even better sign that your yeast is doing what you want.

Just check out how accurate the temperature is when you compare it to the gravity readings. (Gravity readings are in gray.)

Now you can see why temperature cycling is such a good proxy for a healthy fermentation

That said, there's one thing that absolutely can't be beaten...

Great indicators of fermentation health.

Taste testing alongside gravity readings. Whether you're a homebrewer or a pro, you really can't beat getting a feel for what your brew should taste like at each step of the process. Our sours are really rangy on days two and three. If they taste great on day three, we almost never get the final complexity we're aiming for.

Doing regular taste tests when you get your gravity readings paints a great picture of what's going on in the tank and where the brew is heading. Sometimes there's something you can do with this information (like add more/different yeast or adjust the fermentation temperatures) and at other times you can only cross your fingers, hope for the best, and try to tweak things next time.

In the end, creating an optimal environment for your yeast friends is a very complex but rewarding part of fermentation. Not only will your brews be better, but it's just nice having a good, reliable fermentation going on.

If you want to learn more about various fermentations, I highly recommend checking out our books. I especially recommend The Art of Fermentation and Make Mead Like a Viking.

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