Words by Will Keeble
When we talk about sulfur and beer, it’s very easy to be drawn into thinking that it’s all stinky, like cabbagey DMS or worse, eggy hydrogen sulfide. But there are some really useful forms of sulfur in the brew house that can bring out tropical flavours, tweak flavour balances and even extend shelf life.
Depending on how much you paid attention to your chemistry teacher at school you may be finding the way I’m spelling sulfur peculiar, wrong or even a touch American. That’s because it is American! Despite being worth three points fewer in Scrabble; through sheer belligerence, and as the Brits are rather outnumbered on this one, the British spelling of “Sulphur” has been dropped by the scientific community in favour of the American “Sulfur”.
It may feel like sulfate and sulfite can be used interchangeably, and they often are, but there is a real difference. When we talk about sulfate (with an A) we’re talking about an atom of sulfur with four oxygen atoms attached. The amount of sulfate in your beer (and the ratio of sulfate to chloride but that’s a whole different conversation) will affect how much emphasis on hop character and bitterness a beer will have. A drier, cleaner finish is perceived with high sulfate content although levels above 200 parts per million (ppm) should be best reserved for the hoppiest styles like IPAs.
Sulfite (with an I) is a sulfur atom with three oxygen atoms attached. How much of a difference can one oxygen atom make? 1 oxygen atom is the difference between the intoxicating ethanol and dangerously toxic anti-freeze; glycol! It makes a big difference in the science behind sulfur too. Sulfite is a key antioxidant present in beer. That may be down-playing it slightly, sulfite is the boss, the president of antioxidants. Most brewers, vintners and distillers know that oxygen is the enemy of freshness. If you’ve ever left a beer out over-night and smelt it the following day you’ll know what I mean. Post-fermentation, we do what we can to avoid oxygen getting into products, but why?
Even with best practice and a diligent approach, dissolved oxygen will end up in products. It’s not the standard oxygen from the air that does the damage, it’s what it turns into that’s the problem. Oxygen is turned into things called reactive oxygen species which, as the name suggests, are very reactive. They will react with all sorts of compounds. They’ll turn ethanol into acetaldehyde (a dry green apple flavour), fruity smelling hop compounds into sherry smelling species and create papery, cardboard like flavours.
It’s possible to radically slow these oxidation reactions in a couple of different ways. You can slow down the formation of the reactive oxygen species by removing some of the metal ions that help make them. These are extracted from malt during mashing and can be removed with products like Brewtan B. The second way, the way sulfite excels, is by attaching the reactive oxygen species before they can do any damage. These sulfites also have the added bonus of taking previously unpleasant flavour molecules and ‘binding’ them up into new compounds that aren’t nearly as flavour-active.
We can get sulfite from a number of different sources. If you already have the good fortune of using our Finest, Finings Adjunct or Cellabrite then you’re already getting some benefit from the master of antioxidants. Normally in the range of around 2-4 ppm, this will become important later. Yeast gives off sulfite as it ferments. It’s a defence mechanism, stopping other competing microbes from growing. Sulfite quantities from yeast strains can vary even from fermentation but never to levels, in ale yeast, above a few ppm (they’re the highest in lager strains). For wine strains of yeasts, low sulfite yeasts produce no higher than 20 ppm with high varieties producing up to 80 ppm.
In brewing, the difference of 1-2 ppm of sulfite can make a notable difference to the shelf-life of a beer. Although, they won’t impact how stale a beer will eventually get when left in the shed or boot of a car over the summer, they can slow down how quickly the effects of poor storage will take effect.
It’s possible to add extra sulfites to beer and wines using a variety of Murphy and Son products . Additions like 1.52 g Sodium Metabisulphite per hectolitre gives 10 ppm and 1 Metab per hectolitre gives 11 ppm of sulfites. Other products like potassium metabisulfite, Salicon liquid and KMS add sulfites too.
Now, unfortunately, comes the legislative bit… People can experience sensitivity to Sulfites, around 1 in 40 of those who suffer with asthma, presenting as a range of asthma-like symptoms, and some may even develop allergies towards sulfites. Because of these effects, sulfite or sulfur dioxide levels above 10 ppm are one of the 14 allergens that need to be declared. During the brewing process it is unlikely that sulfite levels above 5 ppm will be reached naturally and the quantity will continually be used up in sulfites fight against oxidation. The Brewers of Europe had this to say on the addition of sulfites:
“With a view to guarantee that no complaint can be raised against the industry, The Brewers of Europe recommend labelling when sulfur dioxide or sulphites have been added and it is reasonable to assume that the total content of sulfur dioxide and sulphites, both added and natural, will exceed the 10 mg/litre threshold.”
So there you have it; sulfur isn’t all eggs or sweetcorn. When added properly its longer shelf life, more attuned flavour profiles and wonderful tropical thiols. Keep an eye out on some up and coming Murphy’s products that use pomegranates and tree bark to help our ol’ chum sulfur out.