New World Winemaker Blog

Now you probably wonder what old Jack Sparrow had to do with this…Interestingly enough, Stinkpots, favorite weapons of pirates, were malodorous concoctions made from saltpeter, limestone, asafetida (a vile-smelling gum resin), and decayed fish that were packed into earthenware jugs, ignited, and hurled onto an enemy ship…

Most of us had to manage a stinkpot brewing in our cellar at some stage of our lives, whether it was a result of a power failure (load sharing for South African winemakers), too little nitrogen, or just a general struggling yeast population. And then of course, if the H₂S turns into mercaptans… it will just about kill any odorous component remotely smelling of fruit.

H₂S contains sulfur in its most reduced form. Mercaptans are common organic compounds. When aerated, mercaptans can be oxidized to disulfides, which slightly change their sensory threshold and character. The oxidized forms are usually less of a stinkpot. These reductive components have unpleasant odor descriptors, and these can increase post-fermentation. Some of these, such as H₂S and mercaptans, react with copper and can be removed by copper additions, usually in the form of cupric sulfate. In some wineries additions of cupric sulfate is a standard procedure, sometimes with an addition of inactivated carbon. All of us are aware of course that such an addition, particularly on Sauvignons, can reduce the concentration of aromatic thiols with up to 20%… I personally believe a slight element of H₂S might actually contribute to the complexity of Sauvignon blanc.

But what to do? Well, the magic potion arrived in the form of inactivated yeasts impregnated with copper – Reduless®. It can be suspended with water and added to the tank directly after primary fermentation. The wine is racked off the lees after 72 hours. No residues, no potential risk of copper casse forming, but only a fresh smelling, wonderful wine. It has been developed by Lallemand for red and white wines to reduce H₂S, DMS, DES and other stinkpot related off-flavors in wine.

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

Recent crackdowns on doping in sport have made all of us more aware of the effects of performance enhancing supplements. This got me thinking. What if winemakers could come up with a legal magic potion for yeast? Like the magic potion that enabled Asterix and Obelix to defeat the Romans time after time. Something that would give mere mortal yeasts super human (rather super yeast) qualities?

An increasing worldwide trend is longer “hang-time”. Delaying harvest might increase berry aroma and decrease acidity, but it creates a unique problem for our little athletes. Increased sugar leads to increased alcohol levels in wine made with these grapes. Fermenting yeast thus run the risk of being smothered in the alcohol they produce as a result of them snacking on sugar. Fortuitously, there is a magic potion that you can give your yeast to boost their viability during fermentation.

First, let’s look at the definition of sterols: “Any of various alcohols having the structure of a steroid, usually with a hydroxyl group (OH) attached to the third carbon atom. Sterols are found in the tissues of animals, plants, fungi, and yeasts and include cholesterol and ergosterol.” Here comes the interesting part. Sterols and unsaturated fatty acids (UFA’s) are survival factors during fermentation, but oxygen is needed for the synthesis of said survival factors. With insufficient amounts, the yeast cell membrane functions poorly, especially during highly anaerobic conditions and especially with increasing ethanol levels. Inadequate sterol concentrations around flux controlling proteins in the yeast cell membrane cause damage to the cell membrane and ultimately results in cell death (read: stuck or sluggish ferment!). The key role between oxygen and sterols now becomes evident. Simply put, controlled and timely oxygen addition = more sterol synthesis = better ethanol resistance = happy yeast = happy winemaker.

In my previous life, I’ve found it useful to add oxygen to red ferments anytime from a third of the way through alcoholic fermentation, up to halfway. This roughly corresponds with the end of the cell growth phase and research has shown that an oxygen addition of five to ten mg/L has a very positive effect on cell viability. Another trick is to combine oxygenation and nutrient addition with a pump-over or punchdown. Complex yeast nutrients contain inactivated yeast, which is a good source of sterols. The abovementioned trick also counteracts reductivity, which every winemaker deals with at some stage.

Research is ongoing to gain more insights into how yeast sterol uptake and synthesis affects cell viability. Ergosterol is one of the main compounds being studied, but I’ve also read a paper which outlines the addition of cholesterol to a fermentation! Fermenting yeast are just as happy with cholesterol as they are with ergosterol, but I seriously doubt if winemakers will be chucking cholesterol by the bucketful into their wholesome red wines!

Bernard Mocke is a technical consultant for Oenobrands.