Ask the Experts: Causes of Over Carbonation in Beer

Homebrew expert Brad Smith, author of the Beersmith homebrewing software and the voice behind the Beersmith podcast, discusses the causes of overcarbonation in beer.

Brad Smith 1 year, 11 months ago

Ask the Experts: Causes of Over Carbonation in Beer Primary Image

A Craft Beer & Brewing Magazine reader recently asked us the following question:

I’ve recently started brewing with extract and my beers have been consistently over-carbonated. What could be the cause?

There are several possibilities, including too much carbonating sugar, bottling too soon, and using poor-quality malt or yeast. Let’s walk through each of these one at a time.

First, it is possible you are using too much sugar to carbonate the beer. For example, a lot of beer kits come with a generic amount of corn sugar (or other sugar) to be used for carbonation. It’s not uncommon to see a package of 5 oz (142 g) or more of corn sugar. However, to achieve an average level of carbonation on a 5 gal (19 l) batch, you really only need about 4.2 oz (119 g) of corn sugar.

You can also run into similar problems if you try to measure carbonation sugars by volume. Old books often had things such as “2/3 cup of corn sugar” to carbonate. Not surprisingly, corn-sugar density varies depending on source, so 2/3 of a cup could be too much or too little.

To avoid both of these issues, I recommend you calculate the proper weight of sugar needed using software or an online calculator and then weigh the corn sugar (or other sugar) to get an exact amount.

Another possibility is that you simply bottled your beer too soon. When you do this, the beer will continue to ferment in the bottle, over carbonating your beer. Many new brewers are quick to bottle their beer so they can enjoy it. More experienced brewers are a little more patient. Don’t rush to bottle your beer just because the bubbler on the airlock stopped bubbling.

Use a hydrometer and make sure you have a stable finishing gravity for at least a few days. If you can, give it another week after you think fermentation is done. This will give you some extra insurance to make sure fermentation is done before bottling and also aid in developing clarity in your beer.

Finally, it is possible that the quality of your ingredients led to over-carbonated beer. Low quality or older malt extract, for instance, can often ferment and finish much more slowly than fresh malt extract, again leading to continued fermentation in the bottle. The same can happen if you use poor-quality yeast or an insufficient quantity of yeast. So whenever possible, only brew with high- quality fresh malt extract and a sufficient quantity of fresh yeast.

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