New World Winemaker Blog

In the aftermath of the Southern hemisphere harvest, some poor unfortunates are still struggling with stuck fermentations.  In most cases when looking at the facts one can pinpoint why the stuck occurred, but on the odd occasion the reason is not very clear. I had a situation last week where the winemaker, who also happens to be a consultant to other winemakers, had one of these un-explainable stucks. (I think I’ve just created a new word.) He did everything by the book, made all the right choices, grapes were of good quality, etc. Naturally, the first instinct of winemakers when they see the RS remaining the same for more than a week is to consider re-inoculation. Now, this is where the good news comes in. It seems that there is a miracle product, called yeast hulls, which can potentially save you this costly, time consuming, hair pulling, teeth gnashing, and no guarantee that it will work experience.

Yeast companies recommend the use of pure yeast hulls as part of a re-inoculation protocol. The science behind it is that the yeast that got stuck was under stress to survive and as a result produced medium chain fatty acids. These medium chain fatty acids are toxic to the fermenting yeast as well as to the new yeast used for re-inoculation, as well as to MLF bacteria. So one has to “detoxify” the must first before inoculating with new yeast.  The recommended contact time with yeast hulls before starting the re-inoculation process is 48 hours.

However, I have seen on more than one occasion that the addition of yeast hulls can lift the inhibition on the stuck yeast, with fermentation starting again and completing without the need to re-inoculate. Over time I have come to identify a possible scenario where such a phenomenon is possible. It seems that if the total yeast count is more than one million cells per ml and the yeast viability is 30% or more, then there is a chance that the fermentation might pull through. Depending on the other existing must conditions it might not be possible for the fermentation to go bone dry, but it might get the wine into a “blendable” (another new word? poor English?) condition.

In the particular case I dealt with last week the wine had an RS of 12 g/l. The wine was stuck at that sugar for over a week. The winemaker added Bio-Springer yeast hulls at 40 g/hl and the residual sugar went down to 3 g/l in less than a week.  His yeast cell count and viability were over one million cells per ml and 30% respectively.  In other cases that I am aware off where yeast hulls allowed fermentation to complete, the product Extraferm from Oenobrands was used at a dosage of 50 g/hl.

I am not a non-interventionist winemaker, simply because I do not trust fate at the wheel of my winemaking career.

We are often warned of the danger of processed food to our health, but what constitutes processed food? The common definition of processed food is any food that is handled through a process. Basically slaughtering and animal to get meat, or picking or handling food constitutes a process that leads to processed food. William S. Burrough’s name of his novel “Naked Lunch” refers to the fact that food is never as naked, as it is at the end of a fork. But the purest would argue that often food is not “raw” anymore, but “dead” by the time it is naked at the end of your fork. Is wine natural by the time it is in your glass? My current winemaking philosophy is that I do not want add anything to wine that will take anything away from it.

Basically I do not want to add fining agents, as far as possible, while at the same time I would consider tannin additions, acid and similar additions that will add something to the wine and make it better, more favourably. Dominique Delteil always warned of the effect yeast has on a wine’s colour, because the proteins in the cell wall would bind tannins that are bound to colour, and thereby reduce he colour of the wine. The real world effect of yeast reducing colour is difficult to fathom, but the possibility and effect exists.

One should therefore in theory either use wild yeasts (very small amount of yeast) or yeast that you know will do the job of fermentation well, so you would not need to re-inoculate and thereby fine some colour out with the new yeast cells. One of my pet peeves is the economical use of the truth by chemical and additive suppliers. Their graphs show the speed and efficiency clearly visible on their graph at presentations. They never ever show the correlation of their product with quality.

Does speed of malolactic fermentation correlate with quality? Was their microbial experiment that they used to get the data from, representative of the whole industry? When I buy malolactic bacteria, imagine my reaction, when together with my expensive packet of bugs, I am given a bag of yeast hulls, to help along the kinetics of the malolactic bacteria, and to help fine the colour out of my wine.

What??

Wine is a complex soup of chemicals, with interactions and kinetics quite impossible for any human brain to fathom exactly. Just because there is potassium in potassium metabisulphate, will it affect the pH of my wine significantly? Will my wine treatment improve the quality of the wine, or will throwing salt over my right shoulder have the same effect? I have said it many times, may we never stop learning, and wondering what is around the next corner.

Louis Nel is the owner and winemaker of Louis wines in South Africa.