How Does Chill-Filtration Affect Whisky’s Flavour?
Long chain fatty acids (LCFAs) have sparked much conversation within the scotch whisky multiverse over the years. These tyrants of turbidity are the architects of making some whiskies go cloudy once water or ice are introduced. Hence, they are routinely removed in some whiskies through chill-filtration. But does chill-filtering whisky affect its taste?
A conclusive answer is yet to be published, however, recent studies on baijiu (China’s national spirit), have shed new light on how LCFAs interact with key aroma compounds, and the results are both enlightening and surprising. These findings could have profound implications for scotch whisky, particularly as interest in mouthfeel and texture grows.
What Are Long-Chain Fatty Acids?
LCFAs are non-volatile, high-molecular-weight compounds found in distilled spirits. Unlike esters or phenols, which burst into the air and create immediate aroma impressions, LCFAs don’t evaporate easily. Instead, they remain in the spirit, only making themselves conspicuous under certain circumstances.
Common examples include palmitic acid and stearic acid, both of which are naturally occurring in whisky production. During fermentation, yeast breaks down lipids naturally present in barley, producing fatty acids and their derivatives. Some LCFAs are essential for yeast health, and while most are consumed in the process, trace amounts remain in the final spirit.
Malt scotch whisky is traditionally distilled using pot stills, which allow a broader range of compounds to be carried over into the final distillate than grain whisky that is produced in column or continuous stills. This includes some heavier fatty acids. But it doesn’t end there. Over years of ageing in oak barrels, whisky also absorbs lipid-like compounds from the wood.
What’s The Problem With Long-Chain Fatty Acids in Whisky?
Many Scotch whiskies bottled at less than 46% ABV can develop a haze when exposed to cold temperatures or when water or ice is added. While this hazing has no impact on flavour or safety, it can be visually unappealing to consumers and distributors. To maintain clarity and market appeal, many large scotch brands use chill-filtration to prevent this haze from forming.
The haze itself results from flocculation, a process where microscopic compounds cluster together. The primary culprits are ethyl esters of long-chain fatty acids and larger alkyl esters, which originate during whisky production and can be influenced by distillery-specific cut points. After forcing flocculation (clumping) through chilling the spirit, long chain fatty acids can be removed by passing the spirit through a fine filter.
An alternative to chill filtration is simply bottling at 46% ABV or higher. At this strength, the risk of haze forming in the bottle is minimal. However, once water or ice is added, the ABV drops, and flocculation can still occur. This explains why higher-proof whiskies remain clear in the bottle but may still turn cloudy when diluted.
For whisky purists, the natural haze defence of a higher abv is often the preferred choice, as chill-filtration is believed to remove compounds that may contribute to texture and mouthfeel. But as studies on baijiu indicate, the story doesn’t end with mouthfeel.
How Does Chill-Filtration Affect Flavour?
Due to the fact that they are non-volatile (i.e they do not smell of much), these compounds often go unnoticed, but in baijiu research, scientists are beginning to decode their impact on flavour perception. What’s the difference between baijiu and scotch? Like scotch, baijiu can be made from various grains, but also sometime from rice too. However, rather than been matured in oak casks, clay pots are used instead.
One study on Baijiu found that LCFAs, particularly oleic acid, suppressed the release of important esters like ethyl acetate (pear drops/nail varnish remover odour) and ethyl hexanoate (apple peel odour). This means that spirits with higher LCFA content may have a more muted fruity/estery aroma profile, as the compounds that typically define these aromas are held back.
However, ethyl butyrate, which contributes a rich buttery note, was enhanced instead of suppressed. So while some aromas may appear less intense, the opposite seems to be the case for others.
Research on ethyl palmitate, an ethyl ester of palmitic acid, revealed that it alters the partitioning and release of volatile compounds in a liquid. Instead of a quick burst of aroma, flavours are released more gradually, leading to a lingering, evolving sensory experience.
The researchers analysed a fragrant extract using headspace gas chromatography mass spectrometry (HS-GC/MS) and olfactometry evaluation to compare how 10 different aroma compounds were released with and without ethyl palmitate present. In simple terms this allowed them to measure the molecules being released, rather than relying on sensory analysis alone. The findings showed that ethyl palmitate altered the way volatile compounds are released, making them less detectable and reducing their concentration in the air.
Mouthfeel and Lipid Oxidation
Another study on Baiju highlighted how LCFAs play a significant role in the “softness”, “remaining taste” and “aroma sensation in the mouth”, for baijiu at least. LCFAs were associated with roundness, making spirits feel smoother. This aligns with observations in scotch whisky, where LCFAs are anecdotally associated mouthfeel sensations. But the wormhole goes deeper still. Let’s talk lipid oxidation.
If you recall from earlier, LCFAs are derivatives of lipids from grains. Lipid oxidation is a chemical process where lipids degrade due to reactions with oxygen. This reaction is typically initiated when polyunsaturated fatty acids in lipids come into contact with oxygen, resulting in the formation of free radicals. These free radicals cause a chain reaction, breaking down the lipids into various compounds like aldehydes, ketones, and other flavour active molecules.
The upshot of this complex chemical chain reaction, is that new flavour active compounds, such as aldehydes, can be created in the mouth via oxidation and interaction with proteins in the saliva. So rather than LCFAs impacting the volatile odour molecules that emanate from the glass, they can also be responsible for new flavours that are only created during the process of taking a sip.
What Does This Mean for Scotch Whisky?
Obviously we need to apply a liberal pinch of Campbeltown salt when applying baijiu research results to scotch whisky as they are two very different spirits. However, they share many of the same esters and other volatile compounds, and the possible implications for whisky are intriguing. The implications have the potential to shift the narrative around chill-filtered whisky altogether.
While the conversation has previously revolved around the topic of mouthfeel sensations such as textures, it’s clear that LCFAs could have more profound and unexpected impacts on a whisky’s character. Do LCFAs reduce the volatility of some fruity esters? Are some volatile compounds released at a slower rate in the presence of LCFAs? Do LCFAs increase the detection thresholds of some whisky odours, making them harder to smell?
As with most conversations around flavour, we find ourselves back at its subjective nature. We all experience the smell, taste, and flavour of things differently. Furthermore, our own thresholds change on a daily, and even hourly basis due to emotional state, fatigue, stress levels, and such.
Applying a blanket statement around whether LCFAs benefit a whisky’s character or hinder it is therefore not possible. If the implications from baijiu research are also relevant to scotch whisky, at least to some degree, then certain whiskies may benefit from LCFAs, whereas others may not. But it will largely be a case of personal taste.
Looking beyond mouthfeel, the impact on aromatics is worth considering, especially for high ester whiskies that have a pronounced pear drop odour that is often associated with immaturity. LCFAs may reduce such odours and assist in the maturation of the spirit. However, LCFAs may also reduce the aromatics in ways that are not desirable. They may mute the aroma of some whiskies, making them less pronounced and vibrant.
So rather than discussing whether the chill-filtration of whisky is a good or a bad thing, a more apt conversation surrounds which whiskies benefit from it and which whiskies do not. But here’s the thing. When the chemical diversity of a dram interacts with the neurological enigma of flavour perception, it all gets rather complex, rather quickly.
Hence at The Sensory Advantage, we believe the greatest value comes not from analysing production methods, but from promoting sensory understanding. Once fermentation times, copper stills, and cask types have all been put to one side, we find ourselves with just a single dram, our five senses, and this abstract perception we call flavour. Which, after all, is what it’s all about.
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