Monday 31 May 2010

Flavour Compound of Last Week - Sulphate

Sulphate (SO4), or if you are American or illiterate, sulfate is common in most water supplies where it exists as a counter ion to calcium and magnesium. In beer it accentuates bitterness and at high levels makes this bitterness harsh. Yeast tends to metabolise sulphate into the malodorous hydrogen disulphide and sulphur dioxide. Why then would you want any in beer? Well, as indicated previously sulphate is required to balance the full palate sweetness conferred by chlorides.

The waters of Burton are quite high in sulphate so beers from this area have historically been dry, bitter and smell like the barman has farted in your pint glass before pulling the pint. These days all breweries adjust sulphate levels to achieve the desired flavour profile so the Burton Snatch is less prevelant than it used to be. Strangely some people still find the aroma of flatus in a beer appealing.


Barry M said...

A chap in work has his own water supply that must be pretty rich in sulphates of some sort, or at least it smells pretty rotten eggy/sulphuric. He claims it makes wonderful tea, and certainly drinking it, with or without whisky, it's fine. I'd been thinking of asking him for 30 litres or so to do a home brew with it, but your description of anal vapour has put me off a bit :)

Stuart Howe said...

A lot depends on yeast strain Barry. If you get a strain with low H2S production characterics you could get away with it. If the water supply smells suphidic it's probably not suitable for use in brewing.

Rob Sterowski said...

This reminds me of arguing with a chap who maintained that sulphur in beer was caused by the yeast, I said it was the water. Soon after I was talking to someone from Marston's and he made the, with hindsight, obvious point that the yeast can only produce sulphur if there's sulphate in the water to begin with.

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