New World Winemaker Blog

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.

Working for a company who exports its products to all the major wine producing countries I have been exposed to a fair deal of international travel, mostly providing technical support to winemakers on all matters fermentation. Having done this for over ten years I have had some, well…, interesting experiences. I recall a certain dinner with German winemakers…

 

This concept of having a dinner with a group of winemakers started in 2005. About 10 – 13 winemakers get together and we taste their wines. They give a short description of how they produced it and then we discuss the taste. The evening usually starts very formal and ends in a bit of a brawl. In 2005 I did my powerpoint presentation before we tasted any wine. In 2006 we were at a different, much smaller venue and initially I could see no part of a wall that can be used as a backdrop for a powerpoint presentation. We also started tasting and eating immediately. The wines were of exquisite quality and I thought I was off the hook. About two hours into the tasting, with the decibels now being slightly elevated and more than one person speaking at a time, I was told that I will now indeed be doing my presentation. However, not being able to take part in the very German conversations (I don’t understand or speak any German) – I off course concentrated more on the tasting of the wines. All of a sudden there was a big commotion and various plants and murals were removed from the little room where we were sitting, revealing a perfectly big, suitable, white wall instantly decorated with my powerpoint presentation. A projector seemed to have materialised out of nowhere! I was horrified. Since I have had a few glasses of wine by this stage (fortunately German alcohols are not as high as new world wines) I quickly wolfed down about a litre of water and assumed the position. Fortunately presentations in Germany are very effortless because this one winemaker, if he is present, does them for you. I spoke about two sentences and he “translated” for the next 15 minutes; obviously added a significant amount of his own opinion.

 

After my presentation the evening went downhill very rapidly. Various people were talking at the same time as the winemaker presenting his wine, and the portions poured into the glasses for tasting became bigger and bigger. The speed of wines being hauled out from what seemed to be an endless reservoir increased dramatically. The table looked like the morning after a New Year’s Eve party. At twelve we still tasted wines and there was no indication that the evening was coming to an end – and this was a week night! At approximately 12h30 I took a taxi back to my hotel – leaving behind what seemed like a bachelor’s party at its peak. The next morning I learned that the party ended at 3h30 with beers at the hotel. All the winemakers looked very fragile.

 

The wines at the dinner were really good quality, fresh, aromatic and surprising very New World in style. They also retained the typical varietal character of these German varieties as well as the slightly minerally character that is synonymous with better quality European wines. In short – they were still very German – but much better quality than what I tasted in previous years. This had a lot to do with winemakers using wine yeasts that promote new world style wines at low fermentation temperatures (for the whites). This dinner was certainly very informative for me in terms of the quality of modern German wines, as well as to the winemakers and our distributors; despite it having been a bit of a twilight zone experience.

Every year after harvest I get verbally abused by some winemaker or winemakers regarding the alcohol concentrations in their wines.  Apparently they did everything exactly the same as previous years, used the same yeast and all of a sudden the alcohol is 15% instead of 14%. “What did you do to the yeast,” is usually the question. Doing this job for over ten years I am afraid my tact has become less – not that its ever been great – but my stock standard answer is usually that we decided to put some jet fuel into the growth media, whip out some old ACDC and Kiss records (had to dig for those), play them to the yeasts at full volume during production in order to put some hair on their little chests, thinking “this year we are going to nail the winemakers!”

 

OK so you get my sarcasm. We don’t “do” anything to the yeasts to increase its ability to convert sugar to alcohol. I will spare you the scientific detail but sugar to alcohol conversion is what it is. You cannot get more molecules of alcohol out of a particular amount of sugar molecules. The mystical figure of 0.55 as conversion factor between degrees Brix and alcohol is exactly that – mystical. I do see it making a guest appearance occasionally when people ferment red wine with a low sugar in an open top fermenter, in a well ventilated room, punching down every two hours. In this case the conversion “appears” to be low because a significant amount of alcohol evaporates. Using the same yeast on a higher sugar must in a rotor tank can result in a conversion rate of 0.62. So what does influence your final alcohol concentration?

 

In my experience “conversion rates” fall between 0.58 – 0.63. I have seen 0.55, but rarely lately since red grapes are usually harvested at 24°Brix or higher where I come from. White wine fermentations are mostly cool to cold in closed stainless steel tanks allowing for very little evaporation so a conversion rate of 0.63 is more common than 0.55. In fact I have never seen 0.55 in white. I am sure it exists somewhere in countries where people still ferment whites without cooling. Maybe in barrel fermented wines? Let me know.

 

There can be slight differences between yeast strains in terms of conversion rates depending on how much of the sugar gets converted to by-products such as glycerol, acetic acid and esters, to name a few. However these differences in conversion rates are so minuscule that it is not worth while getting out of bed for, or base your choice of yeast on. Lallemand did a study a few years ago comparing the alcohol conversions of yeast strains under the same conditions. The biggest difference seen between the yeast with the lowest and the one with the highest conversion was 0.51. I suppose a 14.5% wine is better than a 15% wine but labelling laws allow you to print a lower than actual alcohol. Choosing a yeast with a lower conversion might not be very suitable for your wine style and you could end up having a “lower conversion” simply because your wine is semi-sweet.

 

So until researchers can figure out how to create a non-GMO yeast that naturally turns a percentage of the sugar into white light, you will just have to accept that the higher the sugar – the higher the alcohol, and find other ways to lower the alcohol concentration of wines.

This morning I was looking at some results from MLF trials done in Italy during the 2009 harvest season and once again the benefit was overwhelmingly on the side of co-inoculation of the bacteria with the fermenting yeast. Over the past few years I have seen various research reports, published articles and powerpoint presentations at conferences on the topic of co-inoculation. Every time the co-inoculated MLF result is better than inoculation after alcoholic fermentation and certainly streets ahead of the spontaneous fermentation results. Why is everybody not doing it? Well the answer to that question in my humble opinion is two-fold:

 

1. "Fear” because people think that inoculating for MLF before alcoholic fermentation is completed, can have the bacteria grow on sugar instead of malic acid, and as a result form volatile acidity. This is after all what happens in the case of a stuck fermentation. So the fear is justified, but in the case of stuck fermentations it is the natural lactic acid bacteria present on the grapes that cause the havoc. The specific commercial bacteria trialled and tested in the case of co-inoculation do not produce VA. There exists enough evidence for this now.

 

“2. "Cost” because MLF can happen automatically and it won’t cost you a sent. In these economic times many winemakers go for this option. Some people buy a small amount of commercial cultures and then “mother tank” them. However, to ensure a successful MLF, just like a successful alcoholic fermentation, one needs to inoculate a certain population size. By inoculating less, you could run into a stuck MLF which will cost you more to resolve than what inoculating adequate amounts of the starter culture would have cost you in the first place.  There are various other advantages of using specific bacterial starter cultures versus spontaneous – biogenic amines and sensory attributes to name but two.

 

Inoculating after alcoholic fermentation means you inoculate bacteria into very harsh conditions of high alcohol concentrations and possible non-optimal temperatures, since red wine production is towards the end of summer / autumn and cellar temperatures can drop quite substantially. So, you take your chances with a low inoculum due to “mother tanking” into harsh conditions and you expect it to work perfectly every time? These types of practices make me very nervous. I like things to work. My personal view on this is that if you are into quality winemaking you should not be taking any unnecessary chances. Companies selling bacterial starter cultures can only guarantee a successful outcome to some extend if you follow their instructions and use the bacteria under the conditions they are suitable for.

 

Personally I would go for co-inoculation. Why? Well you inoculate the bacteria into juice with no or very little alcohol. How nice is that for the bacteria??? The temperature is also very optimal for the bacteria since yeast produces a significant amount of heat during fermentation. The only thing is that one should ideally keep the temperature in the mid 20’s (degrees Celsius) since that is what will be optimal for the yeast / bacterial combination. It is anyway a good idea in the case of the yeast as well, since high fermentation temperatures increase ethanol toxicity. In most of the trial results I have seen, MLF is completed when AF is completed. The time saving and energy saving (no heating up of tanks) can have a profound effect on your bottom line. Generally one has to inoculate the bacteria 24 hours after the yeast inoculation. The reason for this is to give the SO₂ that was added at crushing time to bind since free SO₂ can have an inhibitory effect on lactic acid bacteria. With co-inoculation there are no short cuts. You have to use the inoculum size specified by the supplier as well as use only bacteria proven suitable for co-inoculation. Suppliers also specify the yeasts that are best suited for the co-inoculation.

 

So, it will cost you, but you will get what you pay for: a more predictable and reliable outcome and latest research shows there is a sensory advantage as well!!! Sounds like a good deal to me. The company that I am forced to work for since I did not marry into money employs an American marketing consultant who would have ended off this blog with the following words: