I was messing around the forums today and came across a question about carbonating your beer, and since the answer is worth repeating, I guess I’ll share it here on the blog…

The main concern keeping our fellow home brewer awake at night was that when he bottled his beer, he came across the same issue about 99% of us come across… the last bottle doesn’t fill all the way up…

So I guess he wanted to know if it would be ok… or safe to cap the bottle and drink it?

The short answer is yes…

However, there is something to consider… when you prime your beer to bottle it, you are adding sugar to your already fermented beer. The reason you add sugar is to get the yeast to produce CO2 while bottled…

The fermentation process essentially repeats itself when the beer is bottled… basically yeast turns sugar into alcohol when there is oxygen, and it turns sugar into ethanol (alcohol) when oxygen is depleted.

During primary fermentation, the CO2 escapes through the airlock, which is why we get flat beer. However, when it’s in the bottle, the CO2 is trapped.

Initially the CO2 hangs out in the headspace and as pressure builds up, it begins to dissolve back into the beer and that’s how you get those cool bubbles in your beer.

Since the CO2 has no where to go, we need to be careful not to over prime the beer since this will build up too much pressure and lead to beer bottles exploding.

Now, the concern with bottling half a bottle is that, since there is more oxygen, the yeast could end up producing more CO2 than a bottle that’s almost full. I don’t think this would lead to over-pressurized beer bottles… at least it isn’t what I’ve seen happen… my only experience with bottle bombs was from the last bottle I bottled once, because yeast sediment from the fermentor went into the bottle… that extra yeast seems to have produced more CO2 than the rest of the bottles and I woke up to an exploded bottle… luckily all the shattered glass was contained within the box which was stacked up in a closet, boxes soaked up the beer (reducing my cleaning up), and no one was hurt…

Lesson learned?… be more careful when racking to bottling bucket…

I’ve filled up many bottles half way and have never had one explode… I think they are just more at risk of oxidation than anything else at that point…

Temperature is another factor affects the carbonation of beer. The colder it is, the more pressurized the beer will get… this isn’t much of a concern when bottle conditioning a beer, but it is when you are artificially carbonating your beer.

I guess it is one reason why highly carbonated beers are usually best served cold, and flat beers are usually served at room temperature…

Anyways, that’s my tip for the day, and I’m off to go to the gym, even though I just had a Dutch Republic Premium Lager… (it was hard to turn it down!)


    2 replies to "How To Carbonate Home Brew Beer"

    • mex

      Overcarbonation is not a factor of yeast cell count. It’s a factor of fermentable sugars. If your beer finished fermenting properly, leaving little or no fermentable sugars, then chances are greater that bottle bombs will not be a factor. Most people have issues with overcarbonation in bottle-conditioned beers because:
      1. The beer didn’t finish fermenting, leaving fermentables in the finished beer
      2. The priming sugar was not portioned correctly, or
      3. They didn’t consider the amount of co2 that was already in solution.

      Lagers, and other beers that are fermented at lower temps (Kolsch, etc) can finish with more than one volume of co2 already in the beer. Considering the average beer has about 2.5 volumes of co2, those styles can start out halfway carbonated.

      If the priming sugars are not calculated to compensate for this… voila! You have bottle bombs.

      • Jorge

        Well said!

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