New World Winemaker Blog

You may have noticed on wine yeast packets and in the literature that there are mainly two different ways to rehydrate active dried wine yeast. The one procedure is a water only procedure and the other a water juice mixture. The existence of two different procedures on different companies’ yeasts can be quite confusing to winemakers if they would like to standardize their cellar practices. Well the good news is you can. Just pick one that suits you best. The reason why one company – say Lallemand – has the water only rehydration and another company – say Anchor Yeast – has a water/juice rehydration is simply legacy. In the seventies when both companies started to produce and sell wine yeast they just happen to choose different methods and then stuck to it. What is very important is that you follow the method you choose exactly and not take short cuts. Yeast rehydration is extremely important for optimal yeast functionality.

So you might ask why two methods exist in the first place. Well, the best way for me to explain this is that water is what was taken out of the yeast when dried after production, so water is all that’s needed to restore the original cell form. However, water has no osmotic strength, which means that if you do not follow the exact protocol and add juice to the rehydration mixture after 30 minutes, then cell constituents (very small, but very important stuff on the inside of the yeast) can leak out from the high (inside the yeast) to the low (water) osmotic pressure. Simple chemistry. The yeast will lose some or all of its functionality, which could result in fermentation problems. So by adding one third juice to your rehydration mix you add some osmotic pressure – making rehydration more idiot proof. You also provide something for the yeast to start fermenting on right away.

In big co-operative wineries the yeasts for several tanks are rehydrated at the same time. So by the time the winemaker returns to the first tank’s mix – 30 minutes could have passed. In this case the water/juice rehydration would be the safer option.

I don’t have any evidence that one method is more effective that the other if both are followed exactly as prescribed. If anyone out there has experience of one being better than the other then please let me know.

This was a rather boring blog to write. Will have to bring in more humor and opinion in my next attempt. Its useful information though…

The other night I had a most amazing dream, dreaming of a Cabernet Franc that just blew me away. There are a few local (South Africa) examples that blow your socks off, but then there are a dozen ugly Betties. What makes this variety so fickle, with a Jekyll and Hyde personality that sometimes makes you smile, and other times cringe?

Cabernet Franc in its best form is the reason Cheval blanc is amazing, and it is one of the parents of Cabernet Sauvignon. From noble descent yes, but where do the white trash, green and yucky traits come from?

Cabernet Franc has two weaknesses in its armor and one being its susceptibility to virus infection. Cabernet Franc has often been used as an indicator plant to test for the presence of virus, and this leads to vineyards that once performed amazingly in their youth, to become amazingly bad by the time they reach their teens. One vineyard I can remember was a five star winner in Wine Magazine in its youth, and when it was about 15 years old it was one of the worst blocks on the farm. By then another Cabernet Franc vineyard that was still young became the crown prince of this beautiful piece of terroir.

The other chink in its armor is its tendency to produce a huge amount of green flavours. Once green flavours enter a cellar, it will survive a nuclear attack with only the cockroaches to keep it company. It is just about impossible to get rid of. The best way to prevent greenness is to follow vineyard practices that prevent green flavours. One of the few analysis that seems to correlate with greenness is malic acid and this is also correlated with very dense canopies. There is actually a direct relationship between the amount of leave layers over a bunch and green flavours. The simplest way to prevent greenness in the cellar is to error on the high side with sugar ripeness when picking, to prevent dense canopies, and to expose of bunches as much as possible.

To say that you can do nothing in the cellar to combat greenness is a bit of a stretch, but for all practical purposes it is true. Many ways have been described to bring down greenness in the cellar, but the exact impact you will have to determine yourself. Besides these methods, that I will describe in another post some time, the only treatment that is suppose to help is basically cooking the wine, which is simply not on.

Interesting enough, the Asian Lady Beetle (Ladybug) that has caused lots of havoc overseas, produces exactly the green flavours in wine that we want to avoid. Hopefully research to combat the flavour induced by the ladybugs, might just give us the answer to fixing green flavours in wine.

Hooo boy – here’s a goody. It is a fact that some wines do show a hot finish; no question. The question is, why. Most people assume the answer is because the alcohol content is high. To a first approximation this is a faulty assumption.

You can do the experiment yourself at home. Go to your wine store and buy five or six different bottles of, say, Chardonnay from different producers, but all with “high” alcohol contents, say, between 14.8% and 15.2%. Taste them blind. I guarantee some will be “hotter” than others.

“Alcohol” in wine is predominantly ethanol: the 2-carbon alcohol which is the primary by-product of the anaerobic metabolism of sugar by yeast. Pure ethanol does not taste “hot” – though it is astringent on the palate (if you were to drink ultra-pure ethanol your mouth would feel dry inside). However, the “alcohol content” of a wine may also include some isomers of higher alcohols – alcohols with 3 carbons or more in their structures – which DO taste very hot. And some of the oxidation products of alcohols (ketones) taste even hotter. In fact, it is the presence of very small quantities of higher alcohols and ketones – which are called “congeners” in distilled spirits – that make a wine taste hot.

So you are wondering why your hot wine has congeners in it. The answer is pretty simple – stressed fermentations. When yeasts are stressed, they start to pump out all sorts of junk, some of which are congeners. Yeasts are neurotic, metabolically speaking – their normal metabolism gets stressed by a whole laundry list of things: extremes of temperature, low nutrients, high sugar, high alcohol, competition with other micro-organisms (including other yeast), natural and man-made toxins, and more, ranging from the increasingly esoteric to the downright speculative.

So here is the indirect link between high alcohol and hot taste: yeast gets stressed out at the beginning of fermentation if the grapes are very ripe (cell biologists call this “substrate inhibition”), and then again at the end of fermentation by the high alcohol produced from high sugar levels (two factors here: end-product inhibition and cell membrane solubilization). Hurt at the beginning and hurt at the end. Double whammy. And if the fermentation sticks (stops before all the sugar is used up) the yeast used to restart the fermentation are stressed from the get-go – leading to a congener production trifecta.

Heaven help us if bacteria start growing at this point. Bacterial growth will further stress the yeast (quadruple toe loop) and the bacteria themselves are capable of churning out all sorts of crud – the very infernal quintessence.

I’m not saying this happens with every high-sugar fermentation, and I’ve already said that not every high-alcohol wine is loaded with congeners. Savvy winemakers can minimize fermentation problems by harvesting before the fruit is over-ripe (or artfully applying the garden hose if the sugar is really high), by inhibiting growth of spoilage organisms with sulfur dioxide at the crusher, by selecting sugar- and alcohol-tolerant yeast, adding vitamins, nutrients and yeast extracts to juice, controlling fermentation temperatures, adding oxygen, and waiting to inoculate with bacteria for malolactic fermentation until after all the sugar is gone.

But there are any number of winemakers out there who are cripplingly limited by their own philosophy. They must wait until the grapes are at 29° Brix to get the flavors they want, and would never use a garden hose. They won’t, or can’t (as in “organic” wine production) add anything to the juice. They live by the cult of “native” fermentation. Or some believe that they have to inoculate for malolactic before the end of primary fermentation to “get it done”.

I’m not being judgy and saying that any of these things is inherently bad, or good. What is certain is that these philosophical predilections can, and frequently do, result in wines with a “hotter” finish.

This blog was originally published July 2006 in John Kelly’s blog: “notes from the winemaker.“

Karien’s comments on the hype that was made about glycerol, makes me nostalgic. Everybody was caught in the frenzy to find ways to increase glycerol in wines, and people went to extremes to achieve their goal.

 Glycerol is one of the base chemicals used to make dynamite, and the commercial production of glycerol involves yeast fermentation, where SO₂ is added constantly. To protect itself from the SO₂, yeast produces glycerol. Winemakers tried to simulate this effect by stressing the yeast during fermentation. Treatments included adding small amount of SO₂ constantly during fermentation, adding unfermented juice to wine (osmotic shock) and stressing the yeast by cooling it suddenly. Many winemakers (and some of the best) practised fermentation practices where the must was cooled to 10°C, allowed to rise to 15°, cooled quickly to 10°C, allowed to warm etc, to increase the amount of glycerol in the wine.

 All these techniques probably resulted in an increase in the glycerol concentration, but had no effect on quality resulting from the glycerol.