Suppose you could ferment your beer in 4 to 7 days, bottle it and drink it a couple weeks after that… now that would be awesome! In fact many brewers attempting their luck at brewing for the first time do just that… they just don’t know any better…

Possible? Yes…

Best practice? It depends…

See, most new home brewers tend to flood forums (and sometimes my email) with questions about their airlock not bubbling, or whether they have to wait for the airlock to stop bubbling before racking their beer, bottling it or moving on to the next step… and the thing about this is that it’s not about time or about the airlock bubbling away at a high or low rate…

It’s all about what the yeast are doing inside the fermenter or fermentor (how the heck do you spell this?)… anyways…

That’s what this video is about, fermentation… more specifically the second phase of fermentation which we call ‘Attenuation’…

First phase? that’s just when the yeast adapt to the environment right before they start eating the sugar… when they start eating the sugar, they begin to attenuate the wort, or in more simple terms, they start to ferment… this is about the time when your airlock starts to bubble… it can take up to 72 hours for any airlock activity to show up…

The airlock bubbling or not bubbling is not necessarily a sign of fermentation… the airlock bubbles because when the yeast eat up sugar they produce CO2, which builds up pressure and well that pressure escapes through the airlock… if you have a leak, then the pressure will escape through the leak and will reduce airlock activity… sometimes the CO2 will dissolve back into the wort and that can reduce airlock activity… in fact, next time you go bottle your beer notice how moving the bucket may get the airlock going again or at least notice the little bubbles springing up your beer… that’s carbonation!

Ok… I’m getting sidetracked here…

Back to attenuation… all it is, it’s just yeast eating sugar… you make your wort by adding sugars from malted barley into it… you throw in the yeast and they eat those sugars up… sugar makes your water dense (as I show in the video above)…

That’s why you take a Specific Gravity (SG) reading… to see how dense the water is… you take one before you ferment the beer and call it original gravity (OG)… because that where it started…

Then as the yeast ferment (eat the sugar) the density of water drops… you take another gravity reading and call it final gravity (FG)… because I said so… just kidding, it’s because that’s where you finished… well not you, but the yeast…

So next time you choose a yeast strain, check out the attenuation levels and notice how they have a range of 65 to 70% attenuation or 70 to 75% attenuation… that is just telling you that the yeast will likely attenuate or eat about 70 to 75% of all the sugars in the wort…

How fast?

Well, that’s what this whole blog post is about… it’s about watching how yeast don’t seem to give a damn whether we want to drink beer sooner rather than later… as far as they are concerned, they have no boss… they work at their own pace… if they want to ferment the wort in 4 days, they’ll do so… if they want to take their sweet time and do it in 7 or 10 days… they’ll do so…

All you can do is check their work progress by taking a gravity reading and watching how density drops…

Or you can show them who is boss and crank up the temperature a bit… that’ll get them going… but they’ll produce more off flavors…

Speaking of temperature, yeast can be demanding creatures… they don’t like temperature swings… they like temperature to be stable… going up in temperature gets them working faster, but like I said it also produces more off flavors and sometimes fusel alcohols if you go high enough… going down on the other hand seems to put them to sleep… they flocculate and drop to the bottom… by flocculate, I mean they clump together… so keep your temperature as stable as possible and make sure that you have good attenuation…

Treat your yeasties good cause your beer depends on it…

Don’t forget to ‘like’ this blog post on facebook, and leave me a comment below…


    4 replies to "Yeast Attenuation And Beer Fermentation Problems"

    • Stephen

      Hi Jorge,

      Thank you, I am really enjoying your newsletters. This latest video of yours is especially relevant to me at this time, and I would like to ask you a question related to the issue of fermentation temperatures and how it relates to my beer.

      I am brewing my first batch, an extract kit. I started it out at 72-75F and everything was fine. The following week it was sitting at 62-68F and completely stopped fermenting based on hydrometer readings. I warmed it back up to 75F and the airlock bubbled for two full days. After 5 days, I took a hydrometer reading and it had only dropped from 1.021 down to 1.020!! My OG was 1.050 (which was too high by the way) so I do not believe this beer is done fermenting. Up to this point, the beer tasted good, but now it tastes REALLY bad which brings me to my question.

      How can problems with fluctuating temperatures and yeast going dormant and then re-starting affect the taste of your beer? The bad tastes in my beer can only be described as yeasty/bitter/lemon sour/band-aid. It no longer even tastes like beer. Will this bad flavor go away with time, and how can I get my beer to finish fermentation?

      Thanks again for your great website!

      • Jorge

        Stephen,

        Great question… the short answer to your question is that you are putting stress on your yeast by letting your temperature fluctuate and that creates more by-products (esters, diacetyl, etc.)… 2-3 degrees should be the max it fluctuates and it should be only once or twice during fermentation, not a constant fluctuation as in warmer during the day and colder at night… your 10+ degree fluctuations are the problem here…

        Some of your bitter/band-aid flavors are probably coming from the high temperature at which you started although usually it’s closer to 80+ F what causes those flavors… the sour flavors are usually due to poor home brew cleaning and sanitizing practices (I didn’t think this was as important myself)…

        1.050 is not necessarily a high OG, but then again it depends on your recipe… regardless, at 1.020 you’ve attenuated about 60% of sugars, which is not necessarily bad, but if that is the case your beer should be tasting sweet…

        Most of these flavors usually go away with conditioning (leaving the beer siting on the yeast for a couple of weeks after fermentation)… If you are 100% certain that your fermentation has completely stopped, then the only way to get your beer to finish fermentation is to do a starter (use 1/2 cup DME, in a pint of water) and pitch it when it’s at high Krausen… otherwise you should just give it time (leave it sitting on the yeast)…

        My second batch of beer turned out sour… it mellowed out with time, but I know the feeling of having a beer not turn out as good as expected…

        Cheers…

    • Blair Friend

      Great advise , question beer is ready to to bottle when spec grav has stopped over a few days? we just did a brew which didnt bubble at all but spec grav went fro 1050 down to 1020 so we assume the process still went on , do you think thats right?

      Cheers Blair

      • Jorge

        @Blair – Well, you definitely got some fermentation, but 1.020 seems a bit high for a 1.050 OG beer, unless you purposely brewed to have a high finishing gravity… the problem with having a high finishing gravity like that is that you can over carbonate your beer in the bottle and end up with bottle bombs (trust me it’s not a pretty sight)…

        If you need to drive attenuation further down I’d recommend making a one liter starter of some lager yeast and pitching…

        Just because SG has stopped for a few days doesn’t mean the beer should be bottled… in many cases it can, and in some it must… but there will be many cases where it will be better to let the beer sit and mature… learn to be patient with your beer and you’ll have better results…

        Cheers!

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