Why we only add demineralised water to our whisky

As you probably already know, most whiskies are not sold at 'cask strength’, but are typically diluted to between 40 and 46% ABV before being bottled. At Glenfiddich, our expressions are typically bottled at 40% ABV, although our Distillery Edition is bottled at 51% ABV for those looking to try something a bit different.  

We use natural spring water from the Robbie Dhu spring in every step of producing our single malt. But in a small break with history, we now demineralise any water we add to our products after distillation. A few people have asked us why we do that. Well, that’s quite easy to answer; it's done for a mixture of cosmetic and health reasons. Bear with me, and I’ll explain the science behind it.

During mashing and fermentation, a very small quantity of an organic chemical called oxalic acid (H₂C₂0₄) naturally forms in the liquid. It’s a harmless enough substance in low quantities and is also found in many vegetables, particularly spinach and rhubarb.

However, when spring water passes through limestone, as our Robbie Dhu spring does, it dissolves and then carries calcium. Calcium is essential for building bones and maintaining a healthy body, it’s actually very good for you. But when you mix that calcium with the oxalic acid, the two separate molecules slowly combine to form calcium oxalate (CaC₂0₄), a clumpy white solid that isn’t soluble in alcohol or water, commonly referred to as ‘floc’. 

Floc makes the whisky look cloudy in the bottle, and in large quantities it isn’t particularly good for you, and has been associated with kidney stones. It's not harmful in the kind of quantities that would be present in a typical bottle of whisky, but it is bad for your health if it accumulates in your body over a long period of time. In essence, we demineralise our water to remove the calcium, to prevent the formation of calcium oxalate.

If you happen to find an old bottle in the attic with some white sediment in the bottom, it’s still safe to drink. But because we have been demineralising our Robbie Dhu spring water for many years, you won't find floc in any Glenfiddich bought today. Our whisky is still made in the same authentic way, only these days we know a little more about chemistry than our forefathers did, enabling us to create a superior product.

If you’d like to discover more about the water we make our exceptional single malt Scotch whisky with, take a Malt Master Class and find out about the Robbie Dhu spring, the source from which all our expressions are made.

Originally published at Whisky Molecules.