The fermentation stage at Dunphail is fundamental to our whisky making art. It is where we produce the exotic flavours which underpin the character of our single malt whisky.
The design and operation of our washbacks ties together all of our previous production processes – and employs a 7-day (168 hours) fermentation to harness the building blocks of flavour that we’ve already created. Our floor malting and malt preparation, combined with this long fermentation stage, creates the perfect foundation for distilling into Dunphail’s incredibly characterful spirit.
The fermentation stage is where both alcohol and the basis of the fruit-forward flavour of our whisky are first created. It is also the juncture where we utilise the final ingredient of the whisky making process – yeast.
Dunphail features twelve open-topped washbacks, constructed from Douglas Fir sourced from our neighbours at Logie Timber. The design of these will be familiar to anyone who has visited our sister distillery – Bimber in London.
Each washback holds 4,500 litres of the wort that we collected during mashing. And our objective with this stage of our production is to create the initial alcohol and flavour basis that we’re looking for. Once fermentation has been completed, the liquid produced – which will then go on to be distilled - is called ‘wash’.
In order to achieve this, we inoculate our sugar-packed wort with a custom-designed yeast strain. We’ve already cooled down our wort to 20º C – the perfect temperature to allow this yeast strain to thrive in. And the sugar-rich environment of our wort is also extremely attractive to ever-hungry yeast!
For the first few hours after we’ve added our yeast, it spends its time getting used to its new environment. Once it has fully relaxed, it starts to work – multiplying many times over. The yeast converts the sugars that we extracted from our malt and in doing so, it produces alcohol and esters – both of which play their part in creating our distinctive Dunphail flavour profile.
During our 7-day fermentation, the yeast works hard to create both the necessary alcohol and the desirable favours we’re looking for. Alongside this, heat is produced and our open-topped wooden washbacks help to regulate this. This ideal environment allows our yeast to produce the bright tropical flavour notes that will go onto become the defining character of our single malt whisky.
Over the first 3 days, the yeast creates most of the alcohol that we required. Over the remaining 4 days, a number of crucial processes take place. Firstly, the now spent yeast drops down to the bottom of the washbacks – creating the crisp and clean wash we’re seeking. Secondly and most importantly – ester formation intensifies.
Esters (think flavour compounds) are created naturally during fermentation. And we want as much of these fruit-forward flavours as possible. Esters are responsible for the vibrant tropical notes that are the hallmark of Dunphail’s single malt whisky.
We purposefully boost our ester levels through a ‘malolactic’ fermentation. In simple terms – this is the positive interaction of beneficial bacteria that naturally lives on, and just under the surface of, the Douglas Fir wood with the wash that is resting within our washbacks.
This interaction is responsible for forming an appreciably higher volume of fruity-flavours. And as such, the foundations of the flavour profile of Dunphail. It is a process which is absolutely fundamental to our outlook on whisky making. A process which is more than worth our additional effort and patience.
After the full 7-days, Dunphail’s exceptionally fruity wash is now ready for distillation – which we’ll be exploring and telling you all about next.