Beer School

How Homebrewed Beer Goes from Flat to Fizzy

updated May 1, 2019
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(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today’s topic: How homebrews go from flat to fizzy
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Beer’s refreshing fizziness is at least half of what we love about it, and right now, I’m sorry to say it — your homebrew has none. Zero fizz. It’s flatter than a can of soda left out after a party.

But we’re going to change all that. Here’s how your homebrew is going to get its fizz back.

(Image credit: Melissa Ryan)

Talk Like a Brewer

  • Priming: Adding a calculated dose of sugar to the beer just before bottling in order to carbonate.
  • Priming sugar: The sugar used to prime the beer. You can use any easily fermentable sugar, from corn sugar to maple syrup, but be careful to measure the precise amount.
  • Bottle shock: A temporary condition right after bottling where the beer’s flavors can taste unbalanced. This goes away after about two weeks.
(Image credit: Henry Chen)

How Beer Gets Fizzy

Just before bottling, we mix a very small dose of sugar into the beer. This process is called “priming” and the sugar is generically called “priming sugar,” although any easily fermentable sugar can be used.

This sugar is like one last snack for the remaining yeast in the beer — a bonus for being the last yeast left standing! They gobble it up and, as usual, create alcohol and carbon dioxide as a byproduct. This time, instead of letting that carbon dioxide float away through the airlock, we trap it with the beer inside the bottle.

And that is how homebrew gets fizzy! A little extra alcohol is also created, but it will only change your final ABV by a fraction.

Commercial Beers & Kegging

The vast majority of commercial beers are actually force-carbonated by machine rather than bottle-carbonated with sugar. It’s much easier for breweries to control the exact level of carbonation in their beers this way — carbonating with sugar is always a bit less precise and predictable.

As homebrewers, we have this option, too. It’s called kegging, and it’s definitely something to look into if you stick with this homebrewing hobby. You’ll need some extra equipment and space for it, but it’s arguably much easier and more reliable than bottle carbonating.

This beer was slightly over-carbonated and gushed a bit when opened. (Image credit: Melissa Ryan)

What Priming Sugar to Use (and How Much)

We want to give the yeast just enough sugar to carbonate the beer and no more — give it too much and the beer will over-carbonate in the bottle. When this happens, at best, you’ll get a bit of a gusher when you open the bottle, like the one above. At worst, you’ll have some exploding bottles on your hands.

The type of sugar used is also important. I generally like to use corn sugar because it ferments cleanly without leaving any perceptible flavors in your beer. Dry malt extract is another favorite — you’re essentially adding a tiny bit of unfermented wort to the beer! Plain cane sugar (table sugar) is also fine to use, but it can sometimes give lighter beers a bit of a cider-like flavor.

Maple syrup, honey, molasses, and other baking sugars can also be used, but they will leave distinct flavors in your beer. Sometimes this is great! A bit of maple in a brown ale is a welcome thing. Just be conscious of what you’re adding and how it might taste with your finished beer.

The sugars and amounts in the chart below are for a typical 1-gallon batch. You’ll always lose a cup or two of beer through the course of the whole brewing process (which brewers poetically call the “angel’s share”!), and these sugar amounts account for that loss. If you feel like you lost more than two cups of beer, scale the sugar down by a gram or two.

Typical Sugar Amounts for a 1-Gallon Batch

  • Corn Sugar: .80 ounces (22 grams)
  • Dry Malt Extract: 1.06 ounces (30 grams)
  • Cane Sugar (Table Sugar): .75 ounce (21 grams)
  • Brown Sugar: .80 ounce (22 grams)
  • Honey: .95 ounces (27 grams)
  • Maple Syrup: 1.09 ounces (31 grams)
  • Molasses: 1.55 ounces (44 grams)

How Beer Gets Primed with Sugar

Add the priming sugar to the beer just before you bottle it. The easiest way to do this is to dissolve the sugar in a little hot water, let it cool, then siphon the beer on top. This ensures that the sugar is evenly mixed into the beer, so no single bottle ends up with too much or too little sugar. From there, you can siphon the beer into bottles, cap the bottles, and you’re done.

Leave the bottles for about two weeks to make sure they’re fully carbonated, and then refrigerate before drinking.

Brew Better Beer: A Companion to Beer School

(Image credit: Emma Christensen)

I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

With The Kitchn’s Beer School, we’ll teach you how to brew your own beer at home — and brew it with confidence. In 20 lessons and 7 weekend assignments, we’ll get you set up with your own home brewery, walk you through your first brew day, show you how to bottle your beer, and then toast you on your first pint. Ready to brew your first beer? Join us!