A layman's scientific guide

What Gives Whisky Its Flavour?

When we taste whisky we are actually performing a sensory evaluation, using taste, aroma and mouth-feel.

Taste:           

We are able to taste things because receptors on our tongues detect volatiles and cause a chemical cascade which is transmitted to the brain, giving us our perception of flavour.

Aroma:

Nasal detectors are extremely sensitive and can detect up to 1 part per million in highly complex mixtures.

Mouth-feel:  

We use this sense to detect density, viscosity, effervescence, oiliness etc.

The major flavours in whisky

Among the flavours we detect when we drink whisky are: cereal, estery, feinty, floral, woody, peaty, sulphury, winey, but what causes us to detect these flavours?

We’ll start with the main components of the dram.

Water:

 ...contains dissolved solutes, which have a varied effect on flavour

Barley:

 ...contributes towards maltiness, mouth-feel, and the peating level.

Yeast:

...add ferment and esters

Wood:

... The extraction of wood compounds can add an oaky flavour to the whisky, particularly when the whisky is stored in barrels for a period of time.

Stills:

...The shape, tall versus squat can affect what happens to the whisky as it is distilled, and therefore the flavour.

What are flavours?

1. Congeners, make up the constituent flavours in a substance, in whisky there are hundreds. These include aldehydes, acids, esters, and higher alcohols.

• Most alcohols can be oxidised to form aldehydes, these form the ‘bouquet’ in the glass.
• Aldehydes can be further oxidised into fatty acids; acetaldehyde becomes acetic acid.
• Fatty acids can react back with an alcohol to form esters; acetic acid and ethanol become ethyl alcohol. Esters are the largest group of compounds giving pleasant and intense aromas.
• Fusal alcohols are made by dry yeast fermentati

2. Phenolics, are highly reactive characteristic descriptors, releasing flavours such as: smoky, medicinal, tart and sweet.

Peated malt:  Peat is decaying vegetation, traditionally used as a fuel source in Scotland. It builds up over many years in layers which vary greatly with different vegetation, different atmospheric effects etc. Today different peating levels can be ‘dialled’ in at malting and expressed in parts per million.

Phenols are highly toxic, but not in the quantities expressed in whisky. The phenolic content of peat is very high, and therefore usually very noticeable, but phenolics can also come from wooden barrels. In whisky, the simple phenolics come from peat and the more complex phenolics come from oak.