Brew Tips #1: How to tell when fermentation is complete?
So, I decided to start tackling things differently when I'm not talking about a specific batch of beer I'm making, and just focus on one specific aspect of brewing. Today, how to tell when fermentation is complete.
If you read a lot of forums you'll hear two things in general. "When the airlock bubbles less than once every X minutes" or "when a hydrometer reading remains the same between 2 readings 48 hours apart".
The latter group will tear into the former with incredible zeal. But I would personally argue that a hydrometer isn't inherently any more accurate than bubbles in an airlock (assuming a properly sealed fermenter and tracked properly of course). But, my opinion is that the hydrometer opinion gets a leg up for only one reason; demanding consistency over a longer period. That aside, I think both approaches are reasonable enough.
Fermentation is the process by which yeast converts sugars into CO2 and alcohol. Thus, as long as there is fermentation, more CO2 will be produced and unless your airlock is plugged it WILL force its way through your airlock and eventually produce a bubble. In that respect it is every bit as absolute as a hydrometer. A total lack of activity in the airlock DOES mean fermentation is complete. Being able to measure a total lack of activity... well that can be time consuming :) which is why most people throw a limit on the delay between bubbles to look for.
Likewise, as sugars are consumed the specific gravity of the wort decreases and so hydrometer readings should go down over time. And, as long as sugars are being converted to alcohol, that will also happen. Again, guaranteed.
Surely the hydrometer is better than the airlock though because it the effects are permanently observable, right?
Good question! That depends. As fermentation approaches the end it gets a LOT slower. Gravity reading may drop but differences may be hard to see. You could very easily write down the wrong numbers. As often as not the gravity land will somewhere between hash marks on the hydrometer and even if you can read it clearly there is no guarantee your recorded value will be accurate. And then there are plenty of reasons why you might get inaccurate readings.
Also, the exact same reasons why an airlock might slow down and seem to stop could also affect hydrometer readings. Like, lets say ambient temperature where you're fermenting dropped and the yeast became totally, or even mostly inactive? That could, in some places last many days. And all of the things you could do to remedy the situation would also improve the accuracy of using the airlock to measure when fermentation stops.
So, back to that waiting 48 hours bit. While it is possible for conditions to un-naturally stop or slow a fermentation which could restart... most of those conditions don't reasonably last 48 hours. So, continually observing the same things either from the airlock or the hydrometer over such a period is a much better indication than any one-off reading. But, more to the point, the notion that even when hydrometer readings appear stable over 48 hours that fermentation is 100% complete is absurd if done at the first point possible to get such a reading. It would be much more accurate to say that it is "effectively complete". In fact, you could probably still wait long enough and observe bubbles from the airlock as proof.
Again, the advantage is actually in the waiting. If the temperature is in the sweet spot for the yeast and you just recently stopped seeing activity in the airlock and you wait 48 hours... it probably wasn't effectively done that first day you observed it (though in many cases it may be close enough not to split hairs over). But 2 days later it almost definitely would be, barring some freak incident where the yeast finally discovered some new source of sugar and sped back up again. Which is really what you're trying to avoid; anything that might turn your bottle product into time bombs (or carbonate a drink you want flat).
So, if you don't have a hydrometer and don't care what the exact ABV of your brew is, don't sweat it. Wait and extra 48 hours and you will almost definitely be fine. Whatever you're brewing just benefits from that bulk aging if it happened to be done originally and potentially saves your butt if it didn't.
I'd also note that everything you brew will be a little different. Waiting times should be appropriate for what you're making. Beer normally only needs days to a couple weeks to ferment. So, adding 48 hours is fine. Wine and Mead take much longer and also slow down and stop over a longer period. Instead of waiting for multiple consistent results spanning 48 hours, you might want to take readings less often and spread it out over a week or more.
Basic point though is to make sure your airlock is tight if you aren't using a hydrometer. And add some time, be it 2 days or more after you think it is done. Every fermented beverage benefits from aging anyway, and even for a beer doing adding 2 days to that is only going to make it better, not worse.
If you read a lot of forums you'll hear two things in general. "When the airlock bubbles less than once every X minutes" or "when a hydrometer reading remains the same between 2 readings 48 hours apart".
The latter group will tear into the former with incredible zeal. But I would personally argue that a hydrometer isn't inherently any more accurate than bubbles in an airlock (assuming a properly sealed fermenter and tracked properly of course). But, my opinion is that the hydrometer opinion gets a leg up for only one reason; demanding consistency over a longer period. That aside, I think both approaches are reasonable enough.
Fermentation is the process by which yeast converts sugars into CO2 and alcohol. Thus, as long as there is fermentation, more CO2 will be produced and unless your airlock is plugged it WILL force its way through your airlock and eventually produce a bubble. In that respect it is every bit as absolute as a hydrometer. A total lack of activity in the airlock DOES mean fermentation is complete. Being able to measure a total lack of activity... well that can be time consuming :) which is why most people throw a limit on the delay between bubbles to look for.
Likewise, as sugars are consumed the specific gravity of the wort decreases and so hydrometer readings should go down over time. And, as long as sugars are being converted to alcohol, that will also happen. Again, guaranteed.
Surely the hydrometer is better than the airlock though because it the effects are permanently observable, right?
Good question! That depends. As fermentation approaches the end it gets a LOT slower. Gravity reading may drop but differences may be hard to see. You could very easily write down the wrong numbers. As often as not the gravity land will somewhere between hash marks on the hydrometer and even if you can read it clearly there is no guarantee your recorded value will be accurate. And then there are plenty of reasons why you might get inaccurate readings.
Also, the exact same reasons why an airlock might slow down and seem to stop could also affect hydrometer readings. Like, lets say ambient temperature where you're fermenting dropped and the yeast became totally, or even mostly inactive? That could, in some places last many days. And all of the things you could do to remedy the situation would also improve the accuracy of using the airlock to measure when fermentation stops.
So, back to that waiting 48 hours bit. While it is possible for conditions to un-naturally stop or slow a fermentation which could restart... most of those conditions don't reasonably last 48 hours. So, continually observing the same things either from the airlock or the hydrometer over such a period is a much better indication than any one-off reading. But, more to the point, the notion that even when hydrometer readings appear stable over 48 hours that fermentation is 100% complete is absurd if done at the first point possible to get such a reading. It would be much more accurate to say that it is "effectively complete". In fact, you could probably still wait long enough and observe bubbles from the airlock as proof.
Again, the advantage is actually in the waiting. If the temperature is in the sweet spot for the yeast and you just recently stopped seeing activity in the airlock and you wait 48 hours... it probably wasn't effectively done that first day you observed it (though in many cases it may be close enough not to split hairs over). But 2 days later it almost definitely would be, barring some freak incident where the yeast finally discovered some new source of sugar and sped back up again. Which is really what you're trying to avoid; anything that might turn your bottle product into time bombs (or carbonate a drink you want flat).
So, if you don't have a hydrometer and don't care what the exact ABV of your brew is, don't sweat it. Wait and extra 48 hours and you will almost definitely be fine. Whatever you're brewing just benefits from that bulk aging if it happened to be done originally and potentially saves your butt if it didn't.
I'd also note that everything you brew will be a little different. Waiting times should be appropriate for what you're making. Beer normally only needs days to a couple weeks to ferment. So, adding 48 hours is fine. Wine and Mead take much longer and also slow down and stop over a longer period. Instead of waiting for multiple consistent results spanning 48 hours, you might want to take readings less often and spread it out over a week or more.
Basic point though is to make sure your airlock is tight if you aren't using a hydrometer. And add some time, be it 2 days or more after you think it is done. Every fermented beverage benefits from aging anyway, and even for a beer doing adding 2 days to that is only going to make it better, not worse.
Comments
Post a Comment