As part of whisky week we ran a whisky themed geological ramble around Loch Leodamais at Port Ellen on the 24th May. We started off with some geological principles, then examined 600 million-year old mudstones and siltstones which had been metamorphosed and folded into shiny, crenulated phyllites about 470 million years ago when these rocks were part of a mountain chain of himalyan proportions. A dolerite dyke crossing the bay was then encountred - it is an igneous rock intruded about 60 million years ago just before the opening of the North Atlantic Ocean. We constructed a time-line in the sand extending from the 'big-bang' to the stone age and put Islay's rocks into a chronological context. Finally we walked out onto the Ard and examined the metabasite sills that were intruded into the mudstone sequences about 600 million years ago and are related to the new oceanic crust that formed in the Iapetus Ocean basin as it opened.
Finally we got round to talking about Whisky!
The water used in fermentation in most of Islay's distilleries is soft, acidic and relatively salty and is sourced from peat lochans close to the distilleries and has little chance to interact with the rocks. However water used in Bowmore and Bunnahabhainn is river and/or spring sourced and is a little 'harder' and has had chance to react with the bedrock (which in the water source areas has a lot of limestone) and this water difference probably creates slightly different chemical reactions during fermentation (which also takes a longer time) and results in spirits which (at least to my taste!) appear to be sweeter.
Whist most distilleries world-wid use de-ionised water for 'cutting' cask spirits down to bottling strength, some on Islay (eg Bruichladdich) use local spring water which contains a wide variety of chemicals - some derived from the ancient 2 billion-year old bedrock - which are thought to give these whiskies extra peaty and salty flavours amongst others. Particular mention of Bruichladdich's 'Mayor of Islay' bottling was made as it is possibly the only whisky with a geological map on the label - celebrating the visit of the mayor from the peruvian village of Islay. Part of Peru has a similar geology to the Rhinns of Islay and both areas were close together until about 600 million years when the Iapetus Ocean separated them.
We concluded that more analyses (and tastings!) are required to fully develop the links between Islay's geology, its water and its whisky.