Sulfidic vs Sulfitic…Ohh the difference a letter can make
While studying for the Master Cicerone exam (a pursuit that honestly feels un-ending!) I came across two words that were so similar I checked several times that there wasn’t a typo involved: “Sulfidic” and “Sulfitic.”
In fact, these two words refer to two different forms sulphur can take on in beer.
“Sulfidic” means containing sulfides and in beer that often (but not always) refers to Hydrogen Sulfide (H2S). Lovers of German lagers know this aroma and flavor well: rotten eggs, natural gas, or sometimes just “very fresh beer.” H2S is extremely volatile so even if you get a big dose in your first whiff of a pint, by the end you may not notice it at all. All yeast produce H2S at some level during fermentation, but some (notably German lager strains) more than others. German lagers are especially likely to hold onto this flavor compound because sulfides are more soluble at colder temperatures, so a cold lager fermentation will hold H2S in the liquid at a higher concentration.
At certain levels H2S isn’t an off flavor at all…it’s an expected (and important) part of many German styles. That touch of sulfide upon opening and pouring means the beer is fresh in many parts of the world! We run into off flavor territory where the H2S is a result of stressed yeast fermentation or infection. In these cases the rotten egg will stick around throughout most of the pint and you’ll perceive it more in the flavor.
Sulfitic beer on the other hand is never OK. This refers to a sulfite, sulphur dioxide (SO₂) at a perceivable concentration in the beer. It has the flavor and aroma of struck match or burnt rubber, or scorched tires. Sulfites are dangerous especially for those that have asthma but they are toxic to all people at levels around 200ppm. For that reason beer (or wine for that matter) with a sulfite concentration over 10ppm must be labeled as ‘containing sulfites.’ However, at 10ppm, the sensory aspect of sulfites is undetectable, the sensory threshold for humans is 20ppm.
Yeast will produce a very small (and very not dangerous) amount of sulfites during fermentation but levels even coming close to 10ppm would come from sulfites added (usually potassium metabisulfite) as an antioxidant or sterilizer.
A lot hinges on that one letter.
If you’re interested in more of the sensory science behind beer, check out my 40-page e-book breaking down the most flavor active compounds in beer.