On the Revised Scottish Whisky Flavour Wheel there is a congener called “mousy”. I personally had no idea how that could relate to whisky, so I asked!
I also did some googling and quickly found out that mousy is pronounces as the small rodent aka mouse, not a desert aka mousse. As a Dutchman I always check if my understanding of English isn’t letting me assume things I thought I know but didn’t. Check out the Clove misunderstanding I had for months.
I also asked on facebook and I was send a link to this page of the aroma dictionary. On this page the mousy note is explained as :
“Mousey taint is a microbiological fault caused by the spoilage yeasts belonging to the genera Brettanomyces and Dekkera, and by the lactic acid bacteria, Lactobacillus hilgardii and Lactobacillus brevis. The compound primarily responsible for the taint is 2-acetyl-3,4,5,6-tetrahydropyridine which is commonly described as ‘mouse cage’, ‘mouse urine’, ‘popcorn’ or ‘corn-chip'”
The next bit of information is a page on the wikipedia site about Tetrahydropyridine.
“Forms of Tetrahydropyridines (abbreviated and often referred to generically by brewers as THP), specifically 2-acetyl-3,4,5,6-tetrahydropyridine and 2-acetyl-1,4,5,6-tetrahydropyridine (abbreviated ATHP or ACTPY), 2-ethyltetrahydropyridine (abbreviated ETHP or ETPY), and 2-acetylpyrroline (abbreviated ACPY or APY) , which are classified as a ketone and a cyclic imine , are commonly attributed to the “mousy”, “urine” (in high amounts) Cheerios® or Cap’n Crunch® (in low amounts), “breakfast cereal”, or more generically, “cracker biscuit” flavour in sour beers”
I have a healthy miss trust about information found on wikipedia, so I waited with writing this blog till I had some more information. I normally use “The good scent company” website as a search option and this time around there was indeed a reference to “mousy” on this page as well. The good scent company also links to a review by Snowdon EM, Bowyer MC, Grbin PR, Bowyer PK., Mousy off-flavor: a review. Journal Agric Food Chem. 2006 Sep 6;54(18):6465-74.
“Although mousy off-flavor occurs infrequently in wine, it can be economically disastrous to the wine producer as, at worst, it can render the wine unpalatable or, at best, decrease the quality of the wine resulting in a lower sale price. Wines infected with either lactic acid bacteria (LAB) (particularly heterofermentative strains) or Dekkera/Brettanomyces yeast can potentially produce mousy off-flavor. There are three known compounds that cause mousy off-flavor: 2-ethyltetrahydropyridine, 2-acetyltetrahydopyridine, and 2-acetylpyrroline. Dekkera/Brettanomyces have been shown to be capable of producing at least two of these compounds, whereas LAB are capable of producing all three. The reason as to why mousy off-flavor forms in some wines and not in others is still not fully understood. The issue is further complicated by the fact that the compounds that have thus far been identified as necessary for off-flavor formation are all potentially available in wine (e.g., ethanol, L-lysine, L-ornithine, and metal ions). For these reasons, the microbe’s metabolism probably plays a key role in mousy off-flavor formation. In the case of Dekkera/Brettanomyces-induced mousy off-flavor, it appears that oxygen may play a key role. Thus, a wine infected with Dekkera/Brettanomyces in the absence of oxygen may not become mousy unless exposed to oxygen via a processing or handling procedure”
The next piece or information I found while reading a book by Gordon M. Shepherd called Neuroenology “How the brain creates the taste of wine”. This book by Shepherd makes reference to a book by Ronald S. Jackson called “WINE TASTING: A Professional Handbook”. I found it online and scanned thru it and here also the mousy note is explained as being an off-odor. Off-odor, Putrid, Mousy, 2-Acetyltetrahydropyridines.
“Certain lactic acid bacteria generate a cloudy, viscous deposit in red wines, in a situation called tourne. The affected wine also turns a dull red-brown, develops a sauerkrauty or mousy taint, and may show spritz if carbon dioxide accumulates”
“Mousy: Several Lactobacillus and Brettanomyces species generate a mousy taint. The odor is caused by the synthesis of several tetrahydropyridines”
All the information I found regarding “mousy” or “mousey” makes reference to the same kind of chemicals. The chemicals are produced by Brettanomyces or in some cases LAB Lactic Acid Bacteria.
The reference to Sauerkraut helps me as a Dutchman since that nose and taste I know all to well since “Zuurkool” is a winter dish in the Netherlands. This last reference made my brain say :”I can spot this note, since I know it!”
How does this all relate to whisky? There are apparently two routes in which this note can occur. One is the wrong strain of yeast being used, or if the culture is contaminated. The other is bacterial which can happen if Lactic Acid bacteria are allowed to grow somewhere along the production of the mash or the wort. cleaning mash and wash-backs is key here.
Both routes of creating these off-notes are explained in detail in the work done by Inge Russell and Graham Steward in Whisky, Technology, Production and marketing, second edition, which I bought for my birthday. Fun read. The only reason I missed it in this book is that this book doesn’t have the word “mousy” in it anywhere, except the diagram of the Revised Scottish Whisky Flavour Wheel. I now also understand why it is in the “Cereal” section of the diagram. In small quantities (cereal/popcorn note) it can be a good thing, in large quantities (pie/sour) it is not.