Bung Hole Sniffing?

I'm sure everyone who has visited a distillery warehouse has had a go at this:

Photo : SpiritAndWood & @MaltMusings

Sniffing a cask's bung hole is an unforgettable experience - the vapours escaping from cask strength whisky are amazing!

The #BlindTastingOnTour gang have a go!

But even if you haven't been lucky enough to visit a warehouse you can do the same with a glass and it doesn't really matter what size your nose is!

Alistair & Max in Cadenhead's Warehouse, Photo : jwbassman_

John & Andy in Loch Lomond's Chemistry Lab.

Distillery managers will wax lyrical about their new make and the aromas you will get from it.

Iain McAllister at Glen Scotia, Photo : jwbassman_

Derrick Smith at Loch Lomond looks on as Mike gets his honker in!

So what is this sniffing lark all about?

 sciencing.com says:

The human nose is made up of an external part with two nostrils and the separating septum as well as internal cavities that filter the air. At the top of the main nasal cavity, located above the mouth's palate, are olfactory hairs responsible for the sense of smell. The function of the nose is to detect odors in the air and deliver warm, clean and moist air to the lungs.

It's the detection of odors that we are more interested in! There are actually two types of smelling: firstly nasal olfaction, which occurs when breathing in, allows us to detect odor molecules from our bung hole or glass. The other is retro-nasal olfaction, which when breathing out, allows us to smell what has been in our mouth.

So when nosing a bung hole or glass you are using nasal olfaction to smell the whisky vapours, then after you've taken a sip and breath out you're using retro-nasal olfaction to add an extra dimension. This is why you get sometimes get different notes when nosing a whisky before and after you've taken a sip, the residue liquid in your mouth has warmed slightly and the odors are being detected as it exits through your nose.

C. Ron Yu, Ph.D of the Stowers Institute says:

Embedded in the membrane of nasal cavity sensory neurons are olfactory receptors. The brain receives odor information from these receptors. When odor molecules communicate with receptors, electric signals travel to the glomeruli in the olfactory bulb.

 Each glomerulus picks up input from the receptor neurons, and expresses only one type of olfactory receptor. The activation patterns in the bulb are believed to signify the specific odors.

Buck and Axel 1991; Laing and Jinks 1996; Axel and Buck 2004 put it like this:

Olfactory receptors consist of protein chains (G-proteins) that penetrate the olfactory cell surface, traversing the cell membrane seven times, and is known as a seven transmembrane segment (7TMr). The chain creates a binding pocket to which the odorant can attach. All odorant receptors are related proteins and differ only in some amino acid residues. The subtle differences in the protein structure explain why the receptors are triggered by different odorant molecules. When the odorant molecules bind to receptors, the conformation of the receptor protein is altered, leading to G-protein activation, then the G-protein turn stimulate into the formation of cAMP (cyclic AMP). These messenger molecules activate the cell, opening the calcium ion channels and trigger a signal to be sent to the brain via nerve processes.

Still with me? So the different odours from our whisky effect different olfactory receptors giving us different experiences. So where do these odors come from? The odors we pick up from a whisky come from the compounds within the liquid, there are hundreds of different ones and they come from the different water, grains and yeast used to produce; and the wood used to mature; the whisky. (This is where my logo comes from!)

Other factors include the peat, if used to smoke the grains, bacteria & wild yeast in the air, fermentation times, temperatures & pressures etc.

Compound Interest explain these compounds in a simple table, although their choice of glass is questionable!

They suggest the compounds include:

Whisky Lactones : A large number of compounds get into the whisky during the ageing process. Amongst these are two compounds that have actually taken on whisky’s name: the whisky lactones. These are, in fact, just isomers of each other, and chemically are named cis- and trans-3-methyl-4-octanolide. Both of these isomers originate from the oak barrels in which the whisky is aged, and both offer a coconut flavour. The cis isomer is the dominant of the two, and has a stronger, spicier flavour.

Phenolic Compounds : Phenols primarily contribute bitterness and smokiness to a whisky’s flavour. They’re particularly noticeable in whisky produced from barley that was dried using peat fires, as is still the case in a number of Scottish distilleries. The burning produces the phenolic compounds in the smoke, which are then absorbed by the barley. Charring of the barrels in which the whisky is later matured can also lead to the presence of phenolic compounds in the spirit. Phenol, cresols, xylenol and guaiacol are amongst the most important phenolic compounds in whisky, in terms of contribution to flavour. Guaiacol is also somewhat responsible for smokey flavours in coffee, and in smoked meats. Compounds called cresols are the culprits when it comes to the oft-mentioned similarity in aroma between Scotch whisky and band-aids. The particular compound responsible is meta-cresol, which has a medicinal aroma, and was also traditionally used in band-aids as an antiseptic. Eugenol is also present in many whiskies, a compound more commonly found in cloves, and partly responsible for their spicy aroma.

Aldehydes : Although not shown in the graphic, acetaldehyde is a feature in many whiskies, representing a large percentage of the total aldehyde content. It originates from the fermentation process, and though some is lost in the ‘foreshots’ during the distillation process, some remains, and adds a pungent, sharp note to the taste. Other aldehydes originate, as with the whisky lactones, from the oak barrels in which the whisky is matured. Syringaldehyde gives a spicy, smoky note, with furfural providing an almond-like, grainy flavour. More familiar is vanillin, the compound that also gives vanilla its aroma. Bourbons are particularly noted for their vanillin content; new casks are used for the ageing of each batch of bourbon, as the vanillin content of the wood is much lower after one ageing cycle. Other aldehydes from the wood include coniferaldehyde and sinapaldehyde. Additionally, some simpler aldehydes such as hexanal can contribute a grassy note in some whiskies, whilst a malty flavour is associated with 2- and 3-methylbutanal.

Esters : A large number of esters are produced during the fermentation process, resulting from the combination of alcohols and either fatty acids, or the acetates produced during fermentation. Many light esters with fruity flavours and aromas are formed, though these are removed in the ‘foreshots’ during the distillation process. These include isoamyl acetate, an ester with a banana-like aroma. The most abundant ester in the ‘heart’ is commonly ethyl hexanoate, which has an aroma described as apple-like. There are a whole range of other esters that can be formed (check out this handy guide to their aromas), and these can be influenced by fermentation conditions. Many whiskies undergo chill filtration to remove much of the ester concentration from the final product. The reasons for this are purely aesthetic, as their presence can contribute to the development of cloudiness in the final product.

Other Compounds : Other compounds in whiskey, outside of the aforementioned categories, can further contribute to its character. For example, two compounds commonly found in roses, beta-damascenone and phenylethyl alcohol, can also be found in some whiskies, and contribute a floral note. Diacetyl, a compound commonly associated with off-flavours in beers, is also found in whiskies, and has a buttery aroma. The presence of some compounds is less than desirable. Sulfur-containing compounds, from the simple hydrogen sulfide to the more complex sulfur-containing aromatic compounds, are the primary cause of off-flavours in whisky. Their presence is reduced by the use of copper stills, as the copper is capable of binding the sulfur compounds, and preventing them from making their way into the final spirit.

Still with me? In 1979 the Pentlands Scotch Whisky Research (now The Scotch Whisky Research Institute) developed  a characteristic description aroma wheel for expressing the aroma of Scotch whisky. It was important that a vocabulary was developed, which was sufficiently large to include all aroma notes likely to be encountered, but sufficiently small to ensure ease of use. Not as easy thing to do but this is what they came up with:

The Whisky Magazine simplified the wheel aromas into 8 categories:

1. Cereal : Aromas from the malted barley, which are usually modified by the later stages of production (fermentation and distillation).
2. Fruity (or estery) : Desirable sweet, fragrant, fruity, solvent-like scents from fermentation and distillation.
3. Floral (or aldehydic) : Leafy, grassy or hay-like scents, sometimes like Parma Violets or gorse bushes.
4. Peaty (or phenolic) : Almost all phenols are imparted to the malt during kilning. The scents are famously abundant in Islay malts and range from wood-smoke to tar, iodine to carbolic.
5. Feinty : Feints come in halfway through the spirit run, beginning as biscuity, toasted scents, then through tobacco-like and honeyed to sweaty. Feints are mellowed and transformed by maturation in good casks.
6.  Sulphury (from organosulphur compounds) : Arise during distillation and maturation. Copper plays a crucial role in removing such aromas, which can be considered unpleasant.
7. Woody : The vanilla related aromas in this group derive from American white oak. Some aromas are directly related to age. Oak increases complexity, enhances fragrance and delicacy, lends colour and develops roundness.
8. Winey (or extractives) : If the cask has previously been filled with wine (mainly sherry, but sometimes others), the wood absorbs wine residues, which are extracted by the spirit and become part of its flavour.

And a much prettier picture:

So next time you take a sniff of a bung hole or from a glass have a read of the table and see if any of the words match what you are sensing. Remember though that all of us have different noses and different olfactory receptors and so smell (and taste) things differently - there is no right or wrong! I might smell strawberry jam, you might smell redcurrant jam - we are both right!

Alistair at The Lakes Distillery

Other important factors affecting the way we nose (and taste) whisky include the location, situation, company we are with, the glass, the mood we are in and all the other things whizzing around our brain as we try it!

But at the end of the day whisky is for drinking, so after you've spend some time nosing your dram, drink it! It's also much better with friends, either in person or virtually!

Photo : jwbassman_

If you're not totally geeked out yet (!) further reading includes a brilliant thesis by Tao Yang, called "The impact of whisky blend matrices on the sensory perception of peaty flavours", available here.