Why do some whiskies taste sweeter than others?

An Introduction
I am about to review the Golan Heights Malt Whisky Single Cask #16 (Cabernet Sauvignon Dry Red Wine) whisky from Israel so this is a kind of a preface to that review. I wanted to understand why this whisky is so sweet.
This led me onto the question as to why hardly any Scottish distilleries produce Dry Red Wine matured single malts, which led me onto an even bigger discussion as to why some whiskies taste sweeter than others?
An even more fundermental question might be: Where does the sweetness in whisky, (or for that matter, Bourbon or Rum) come from?
Dry Red Wine Matured Single Malt Whisky and why there aren’t more of them around
You can find quite a few Red Wine finishes from the likes of Edradour, Arran, Glenfiddich and Glenmorangie but all of these show flavour influences from previous cask types, particularly Ex-Bourbon White American Oak casks:
Edradour 16-Year-Old 2000 - Barolo Cask Finish

Arran 2007 Amarone Cask Finish

Glenmorangie Claret Wood Finish

Glenfiddich “Age Of Discovery” Red Wine Cask Finish
After some Googling I came to the conclusion that there are actually very few examples of Scotch Single Malts which have been matured exclusively in Dry Red Wine French Oak Casks like this Golan Heights. In fact, I only managed to find two examples:
So why aren’t there more Dry Red Wine bottlings?
Well, reading through some of the online reviews you begin to understand why.

Deanston 2008 Bordeaux Red Wine Cask Matured

“The Deanston is described as having an interesting spicy citrus fruity smell but taste is red hot spicy, rough, bitter tannins, unbalanced harsh bitter red fruits.”

Kilchoman 2012 Portugal Douro Valley Red Wine Cask matured

“The red fruits, buttery notes and over-the-top oak makes this slightly overweight and not very balanced whisky makes this my least favourite Kilchoman.”

Fascinating how the Golan Heights Cask #16 seems to avoid the obvious pitfalls of the two examples above.
Why do Ex-Sherry Casks produce sweet whisky?
Well, you might say that this is a dumb question because everyone knows that sherry is sweet and dry red wine is well, it’s dry! But it’s actually not that simple!
Fortified wines such Port and Madeira do have a high sugar content, as well as Rum, and indeed they are exceedingly sweet liquids. Oloroso Sherry used to season the majority of Spanish Sherry casks, is termed a "dry" sherry and can taste somewhat tart and sour drunk straight. Despite this, our brains associate the dark fruity flavours of dates, figs and cherries coming from th sherry cask as "sweet".
Dry Red wine has around 3.5g of carbohydrates per 100g of wine.
Sweet Red wine has a minimum of 7g per 100g of wine and very often much more.
A lot of people enjoy sweet whiskies, hence the popularity of heavy sherry cask matured single malts such Macallan, Glendronach and Dalmore. Less popular are whiskies matured in Ex-Red Wine or Ex-Herring casks (believe it or not, this has been tried) and for obvious reasons.
Many years ago, distilleries used to rinse out with water their Ex-Sherry casks before filling with new-make-spirit because they dafka, did not want such a dominant sherry flavoured whisky. Today, however, distilleries will do anything they can, even stretching the rules of the Scottish Whisky Association to near breaking point (and sometimes beyond breaking point), in order to extract as much sherry fortified wine flavour as they can. Fresh Ex-Sherry casks will still hold a sufficient amount of sherry in sitting at the bottom of the cask (which they sometimes “forget” to pour out), as well as more sherry residing inside the pours of the wood, to significantly influence the flavour of the whisky.
However, Ex-Sherry cask matured whiskies are not the only single malts which are described as sweet. Ex-Bourbon matured whiskies are also often described as sweet or even ultra-sweet but the sweetness is less fruity sweetness in style and more toffee/caramel sweetness style.
Sweet and Dry
There are a number of published articles which discuss the fascinating and surprisingly complex subject of how we identify something as sweet and something as dry.
You might assume at first thought that recognising and categorising a food or drink as sweet was a solely objective process but actually, it is far more subjective than we might think. A piece of apple placed in the mouth will taste sweet but after having drunk some sugary drink, that same piece of apple might actually taste bitter. Those who have a high intake of cane sugar in their diet will be less sensitive to naturally sweet things like fruits and of course, whisky, and will fail to sense subtler flavours in these items.
Malt Whisky Yearbook 2018 Page 47, “Sweet and Dry” by Ian Wisniewski.
Sweetness is perhaps the most dominant and most craved after of the five primitive basic tasting senses which we perceive when putting something in our mouths. The others being sourness, saltiness, bitterness and something which is referred to as savouriness or umami (from the Japanese). This umami is a mouth fill flavour found in meats, soy sauce, marmite and solid cheese as well as cooked grains and beans. Umami was only very recently recognised as a flavour in its own right as, especially to a Western palette, it almost always accompanied by saltiness.
Is calling something dry simply expressing its lack of sweetness?
If asked, many people would express the opinion that dryness is not one of these basic tasting senses because it is simply an expression of a lack of sweetness. Others say that dryness is a combination of savouriness, saltiness and bitterness. Still others insist that dryness is actually a basic tasting sense in its own right, sometimes referred to as tannins or an astringency flavour.
When it comes to primitive survival instincts, people tend to reject foods with an astringent taste as they are associated with unripe fruits which would make you ill or things which are actually poisonous which will kill you. On the other hand, things which are sweet tend to be nutritious.

However, a more sophisticated palate might prefer foods which have a complexity of flavours which while being predominantly sweet, also have a percentage of other tasting notes including dryness, rather than a food which was almost entirely sweet.
A food or drink which contains dryness/tannins/bitterness will give a sense of a fuller body, a complexity in the mouth which makes the item more interesting and characterful, increasing the enjoyment level of the eating or drinking experience.
Where does the sweetness in a whisky come from?
This is a very complex question and I don’t pretend to have a definitive answer, just some ideas.
Most might assume that sweetness comes from plain sugars or carbohydrates that dissolve in the mouth exposing their sugars. Cane sugar is perceived by most as being almost entirely sweet whereas honey is dominantly sweet but with a small percentage of dryness. Incidentally, most perceive artificial sweeteners used in soft drinks as sugar sweet but many perceive an unpleasant bitter or metallic flavour underneath that sweetness.

Corn mash to make Bourbon

Malted Barley flour to make Whisky

sugar-cane-molasses to make Rum


If we taste the mash and then the wort from a washback (after yeast has been added), they both have a sweet flavour from all the sugars in the malted barley. Likewise, Premium Rum, which is made out of sugar-cane-molasses, is ultra-sweet. However, according to nutritional values published for whisky and rum, distillation is supposed to convert all the sugar into alcohol leaving no sugar content at all.  So why is it that those who have ever tasted New Make Spirit straight from the stills will tell you that it tastes fruity sweet like white grape juice, apple or pear juice?

In actual fact, our taste buds and the way our brains interpret those taste signals can sense sweetness from other substances besides carbohydrates. Everyone who enjoys whisky will tell you that one of the main basic flavour profiles is sweetness. Anyone who also drinks American Bourbon will tell you that Bourbon tastes much sweeter than Scotch and assume that the reason is that corn mash, from which Bourbon is made from, is sweeter than malted barley, but aren’t both these whiskies distilled into almost pure ethanol alcohol?
(From whiskyscience.blogspot.com)
"Even though sugars are converted into pure alcohol at the distillation stage, the ethanol alcohol contains esters which are perceived to taste similar to white wine and fruits such as (as mentioned above), apples, pears and even ripe bananas. The brain’s identification of these fruits include a sense of sweetness even though there is actually no sugar in new make spirit. Distillers will tell you that the more copper contact from the stills there is during distillation, the fruitier the New Make Spirit will be. Moreover, the middle of the middle cut tastes sweeter than the middle cut nearer to the tails and heads."
The sweetness of dry wood
When it comes to a liquid such as water, milk, oil, wine or whisky, tasting dryness in a liquid seems like a paradox as our brains are programmed to always associate a liquid as “not dry”. Water can be described as dry if it contains too much calcium or stone.
Interestingly, in Shemos (Exodus) 15:23, the Torah describes the water of Marah as “Marim”, which is usually translated as bitter. In 15:25, Hashem shows Moshe a tree which when thrown into the water, produces water which everyone now perceives as sweet. Interestingly, tree wood influence, raw wood, toasted or charred oak, can have a dramatic effect as to whether we perceive a whisky as sweet or dry.
Sugarless fruity esters sweetness from New Make Spirit, once matured in oak for X amount of years, there is further sweetness coming from actual sugars inside the wood which the whisky has matured in, especially from heavily charred American White Oak casks where the oak sap has caramelised to produce maple syrup like sweetness. Moreover, American White Oak contains a lot of vanillin which the brain might well translate into coconut and ice cream type flavour sweetness.
Previous Contents of the cask influences the flavour of the whisky
With fresh First Fill Casks, there is sweetness and actual distinctive flavours that come directly from the previous contents, be it Bourbon, sherry, wine or rum, which has been absorbed into the pours of the wood.
As well as the fructose and sugars from the sherry, there is a distinctive sweetness that comes from even so called dry sherries such as Oloroso. This is due to very high amounts of a type of alcohol called Glycerol in sherry which imparts a sweet taste at around 40% of the sweetness of cane sugar.
Interestingly, dry red wine contains only very low quantities of Glycerol compared to fortified wines such as sherry, brandy and port.

French, European and American White Oak
American White Oak can impart creamy, vanilla, coconut and maple syrup flavours to the whisky. French and European Oak on the other hand will impart less vanilla sweet flavours and more tannins flavours like brewed tea and stronger wood spice flavours which are interpreted as dry flavours. This doesn’t have to be a negative thing as these same flavours add complexity, body and greater character to the whisky.
Let’s take Rum as an extreme example

Most YouTube rum reviewers tell you that rum is a lot sweeter than whisky and most viewers would take that as a given. After all, rum is made of cane-sugar so must be sweeter. However, as already discussed, once the mash is distilled, it all turns into ethanol alcohol which contains 0 sugars.
After some Googling it seems that most Rums have cane-sugar added to them to maintain the perception that rum is sweeter than whisky/gin/Bourbon. It seems however that this is a myth. A premium rum with no sugar added should actually not taste sweeter than whisky/Bourbon as the sweetness and flavour is coming from the previous content of the cask plus the wood. If a rum and whisky used the same Ex-Bourbon American oak cask then theoretically they should have the same sweetness. Nevertheless, most reviewers will tell you that Rum such as Appleton Estate Premium Rums, always tastes, not just a little sweeter but a lot sweeter than whisky.

I suspect that when it comes to Single malt Whisky and premium Bourbons and Rums, that the distilled spirit and the wood is not the whole story. There is residual of grain oils and other ingredients from the grain/malt type that transfers to the spirit and is not destroyed during distillation. I suspect that a good percentage of flavour character is coming from the grain but I am still puzzled about the source of all that sugar-cane-molasses sweetness coming through. How much of it is coming from the sugar grain or cane and yeast mash, how much from the previous contents of the cask and how much from the wood?
In conclusion, I haven’t answered the question to my own satisfaction but at least I have explained just how complex the question is.



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