In Alcoholic Fermentation and Yeast
January to April 2009 was going to be my tenth South African harvest working as a technical consultant for a yeast manufacturer. However, due to the arrival of the stork with a 3.45 kg female parcel, I missed the entire season due to maternity leave. I was initially ecstatic about the “break” but that happiness was short-lived when I realised it was MUCH easier to advise on yeast than to handle a newborn with colic. Fortunately it passed, as all things do, and after four months I found myself back at work very impressed that I missed all the stuck fermentations…or so I thought.
In South Africa harvest is approximately from January until mid-April. It was June. I STILL had people phoning me with: “I have a stuck fermentation. Can you please help me?” Sigh…in my earlier years I was immediately sympathetic and offered advice into the greatest detail. In the last few years, being an opinionated person with a “sometimes problem with tact” the odd winemaker is subjected to the tiniest level of verbal abuse. Sometimes I only think it but sometimes when the situation calls for it, I say it: “Why on earth are you only phoning me now? At some point during the ferment you must have noticed that it is sluggish? Why did you not phone then?” The answer is always “hope.” Hope…all forms of religions and spiritual beliefs advocate that without hope, we are lost. Winemakers are a species with lots of hope it seems. They hope that after the wine got stuck it will miraculously start again and finish resulting in a top quality wine. I suppose there is some reasoning behind this since I have actually seen this happen in my ten years as a consultant, but “hoping” for this to happen is about the equivalent of me hoping that I will win the lottery.
In 2008 I published a series of articles in the Australian and New Zealand Grapegrower and Winemaker on how to avoid stuck fermentations, how to treat sluggish fermentations and how to restart stuck fermentations (view the pdf of the published article). I view the “how to avoid stuck fermentations” as the most important part in this trio of articles. In my humble opinion, 80% of stuck fermentations are preventable. I am going to say it again…80%. Got it? In my experience 60% of the time winemakers simply used the WRONG yeast for the prevailing fermentation conditions. There are many yeasts distributed by various yeast companies very well suited for the production of Cabernet Sauvignon. Very few of them can ferment 26°Brix to dryness. When a winemaker phones me with a stuck fermentation the first question I ask is: “what was the initial grape sugar at harvest?” The second question is: “what yeast did you use?” 60% of the time I have my answer as to what caused the stuck fermentation right there. In some cases the winemakers did not know that the yeast was not alcohol tolerant enough and in some cases they did know but they….you guessed it….HOPED. In my experience the other 40% of stuck ferments are mostly due to propagation, incorrect fermentation temperatures and/or nutrition.
Yeast is a living organism. There is a limit to what it can do. There is no point in me hoping that I will ever win an Olympic gold medal. Winemakers seem to have this type of hope on a regular basis. So how does one resolve this epidemic of false hope? Well if you read this blog you are halfway there. The answer is “information.” Read the information that is supplied to you and make an informed decision when it comes to yeast choice. Don’t just use a yeast because of tradition or fashion. That way you can potentially save yourself time, money and embarrassment. Stuck fermentations are a reality here to stay. They do sometimes occur for what seems like unexplainable reasons. However, most of the time they occur because of known reasons which means you can potentially prevent them. And for heaven’s sake get help when there is still time to prevent the wine from going south completely. Once you have to roll in the VA and alcohol removal machines the cost of that certain volume of wine skyrockets. Not to mention the potential quality of the wine afterwards.
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