This week I take a look at the practice of using sulfites as a preservative in beer brewing, including the advantages and disadvantages.
Sulfites as a Preservative
Sulfites, usually in the form of Potassium Metabisulfite, are widely used as an additive in wine, mead and cider making. Sulfites also naturally occur as a result of the fermentation process. Sulfur dioxide, often noticeable in many lagers, is an example of a sulfite compound produced during fermentation. Sulfites as a group help to prevent oxidation in a finished beer and also reduce the chance of spoilage by inhibiting bacteria and wild yeasts. They essentially mop up free oxygen in the beer, inhibit the growth of bacteria, and slow enzymatic reactions that age your beer. Sulfites, also known as sulfur dioxide (SO2), can significantly extend the shelf life of your beer by preserving the flavor, color and clarity of your beer. They also can neutralize free radical compounds in beers that can lead to oxidation, stale flavors and rapid aging.
Natural Sulfites from Fermentation
Natural sulfites are a byproduct of fermentation, and typically occur in concentrations below 30 ppm. Lagers often contain 10-20 ppm of sulfite, ales roughly 5-15 ppm, and many specialty beers run somewhere in between those two extremes (Ref: Expertbrewing.com). However most commercial beers fall in the range of 10 ppm or less, and beers with over 10 ppm must be labeled with “Contains Sulfites”. Sulfites are not the “rotten egg” or “burnt match” aroma you get from many lager yeasts.
The production of sulfites during fermentation is largely a byproduct of the yeast you select, but factors like temperature, pitch rates, and pressure can also play a role. Sulfites are created when yeast converts sulfates from the grains into sulfite, so yeast selection is critical.
However as sulfites are a natural preservative, you don’t necessarily need to take extraordinary steps to reduce natural sulfites. As natural sulfites are almost always below the 30 ppm level, they are not typically high enough to broach the flavor threshold or sensitivity threshold for average drinkers.
Adding Sulfites to Preserve Beer
Since sulfites have a positive effect on beer stability and long term storage, why not simply add more sulfites to your finished beer as a preservative? This is very commonly done in the wine industry, but sulfites are also used in cider, mead and a wide variety of foods. But as you might expect there are some downsides. These include:
- Some individuals have a very high sensitivity to sulfites or even sulfite allergies. Many cannot enjoy wines with high levels of sulfites and also have the same sensitivity when sulfite levels are high in beer. As a result both the US Food and Drug Administration (FDA) and European Union (EU) have rules in place that commercial beers containing more than 10 ppm in sulfites must be labeled as “Contains Sulfites” (Ref: ExpertBrewing.com) to notify consumers who might be sensitive to sulfites. Many other countries also regulate sulfite levels and labeling in beer.
- Sulfites can have a flavor impact on your beer. Sulfites are sulfur based compounds and in higher concentrations they can lead to sulfur-like aromas or even staling flavors like cardboard. Because of this, beer brewers generally have to use lower levels than might be used in a wine. See the discussion below regarding what the appropriate levels might be.
Two forms of sulfite are commonly used in wine and beer. Potassium Metabisulfate is the most common addition, and is widely used in wines as well as beer as it is largely flavor neutral. It is also sold as “Campden tablets”. This form can be added to beer, but should be done after fermentation is complete as the potassium can interfere with mash chemistry, and also adding sulfites before fermentation is complete can inhibit regular fermentation. Sodium Metabisulfite is the other common form and can also be added after fermentation, but the sodium can have an impact on flavor so it is rarely used in wines and meads.
Sulfites are often used during the brewing process in low oxygen brewing. Low oxygen brewing is a set of advanced techniques to reduce oxygen levels throughout the brewing process. I won’t cover the specifics of low oxygen brewing but you can read more about how sulfites can be applied to this technique here (Ref: BrewingForward.com).
Sulfite Levels in Beer
What level of sulfites is appropriate for beers? Wine makers commonly use levels as high as 200 ppm (the US legal limit is 350 ppm), though levels of 100 ppm are more common in white wines and perhaps half of that (50 ppm) in red wines. Red wines need less preservative as the tannins and acids from the grape skin act as a natural preservative. Similarly, dark beers are less susceptible to oxidation and aging than lighter beers due both to the melanoidins (dark color compounds from the malt) which tend to produce a smooth sherry as opposed to cardboard flavor as they age. Also dark beers have a richer roasted flavor profile, so off-flavors from aging are less apparent. So we can use less sulfites with a dark roasted stout than we might need to preserve a delicate lager.
As I mentioned earlier, the 10 ppm FDA and EU labeling threshold can be considered the floor for the flavor threshold. Even those sensitive to sulfites will rarely detect them below the 10 ppm level and many beers have a natural level of sulfite from fermentation at or below that threshold. However as we raise the sulfite level in beer, it can create other off flavors fairly easily. The problem is that while sulfites mask off flavors like cardboard (trans-2-nonenal), they can enhance other defects and off-flavors (such as dimethyltrisulfides) in beer. BrewingForward has a section (Sulfite at packaging) here with references, and other studies such as this one by Callemein, Dasnoy and Collin, cover the effect in more detail.
As a result, I think moderation when using sulfites as an additive is in order. Darker beers generally require less in the way of protection, so you might consider not adding sulfites. Lighter beers are more susceptible to staling, but are also more at risk from off-flavors, so again a low to moderate sulfite level is appropriate. I personally would keep the target sulfite level at 50 ppm or less if you plan to add sulfites to your beer.
BeerSmith software actually has a sulfite tool which can help you calculate the amount of potassium metabisulfate to add. While designed for wine, mead and cider, it can also be used with beers. Go to Tools->Sulfite Tool to start the tool. Enter the batch volume at the top. If working with wine you can enter the pH level and it will give you a recommended sulfite level. For beer, I recommend using a target level below 50 ppm, so go now to the Sulfite to Add section. For Free Sulfite you can either enter an estimate of the sulfite from fermentation (typically 10ppm is a good estimate) or you can use a sulfite measuring kit, commonly sold for wine making to actually measure the amount of sulfite present in the finished beer.
Next enter your target sulfite level, I recommend 50 ppm or lower for beers, and it will estimate the amount of potassium metabisulfite to add. As a sample I started with a 5 gallon (19 liter) batch and entered a 10 ppm starting free sulfite level and target of 50 ppm and came up with 1.3 grams needed to achieve this level. The tool also estimate sorbates, which can be used with cider and mead for backsweetening, but for beer you really don’t need to add sorbate.
I hope you enjoyed this week’s dive into sulfites and beer. Thanks for joining me on the BeerSmith Home Brewing Blog. If you want to take the guesswork out of brewing, please try my BeerSmith recipe software from BeerSmith.com. Be sure to sign up for my newsletter or my podcast (also on itunes and youtube) for more great tips on homebrewing.