Like it or not, it looks like hard seltzers and buzzy hard sodas are here to stay!  And that’s good news for brewers and fermenters alike as you’ve already got the equipment and tools on hand to whip up some of these tasty, refreshing beverages.  What could be simple, water, some sugar (usually dextrose) and yeast and you’re well on your way to making hard seltzer.  

The main ingredient in any good seltzer recipe is of course, is water. So that should be the simplest part of your seltzer fermentation, right?  

Well, sort of. In an ideal fermentation, you’ll need two types of water—purified water and also regular tap water. Knowing when to use which kind of water will have profound effects on your final product.

First, remember that in making seltzer, all flavoring should come from the seltzer-maker, and not from the whims of nature. So, it’s important to minimize the chances of accidentally introducing any off-flavors or aromas early on. Start with the water you’re using during your boil. You want purified water—often produced through reverse osmosis—which is water free of any minerals, dissolved solids or municipal water treatment chemicals that could negatively affect your seltzer. Think of it as a blank canvas; purified water will give you the purest white, allowing whatever colors you add at the end to stand out.

The exception comes when it’s time to hydrate your yeast, which awakens them from suspended animation. In this case, plain old tap water is best, because of the very minerals and dissolved solids within it that you wanted to avoid earlier. Those dissolved minerals and solids prevent the yeast from being killed through diffusion.

“Yeast works through diffusion,” explains Blake Bomben, business development manager for Ravago Chemicals North America (RCNA). “If the water has nothing in it, the water starts stealing nutrients from and out of the yeast. That’s the opposite of what you want to happen. You’re trying to wake the yeast up and get them ready to start taking nutrients into their cell and grow, and for that, you need what’s in the tap water.”

Once the hydrated yeast is mixed in with the cooled sugar water that has the proper yeast nutrient added to it, fermentation starts. This is a step where selecting the right yeast and yeast nutrient combination is also critical.  

At the end of your seltzer fermentation, you’ll emerge ideally with a very slightly flavored and lightly aromatic liquid (cold brewed sugar)—a canvas as pure “white” as can be. However, because no two fermentations are alike, you may still detect unwanted aromas or taste profiles. These can affect whatever flavoring you end up using. “If you have any off-flavors, they can fight or mask whatever flavoring you want to add,” Bomben says.

Counteracting these unintended results is the job of carbon, which is added at the end of fermentation but before flavoring your hard seltzer recipe.

Carbon may look like nothing more than a fine black powder, but how it’s made and what it’s made from have dramatic implications on what it can do, Bomben explains. “There are carbons that remove colors, based on certain molecular weights. And there are carbons that remove flavors and aromas, and they’re a different molecular weight. You can even use a mix of two different carbons—one to remove the color and one to remove any negative aromas.”

Note that if you use carbon, you will have to settle, screen or filter it out. Otherwise you will end up with a light grey tint in your seltzer from the carbon fines. One method of doing this is using carbon impregnated filter pads, another is to utilize a “Carbon Snake style purification filter” to remove the carbon before adding the flavorings and carbonation. 

RCNA offers two kinds of carbon. Calgon Carbon’s Acticarbone 2SW is designed to remove odor and taste contaminants, while Acticarbone CEW is a de-colorizing agent. Take advantage of the full list of filtration aids here for any other unwanted contaminations in your water or final product.