Wine Basics: Some Study Notes

I have a quiz coming up next week in the wine course I’m taking. Here are a few things which will probably be on there.

1. What is photosynthesis?

This question reminds me of my days in 9th grade science. Unfortunately, I flunked 9th grade science. If I remember rightly, photosynthesis is when a plant takes carbon dioxide and turns it into energy. Somehow, sunlight is involved. Let’s go to the magic of the interweb to find out more:

Photosynthesis is the process by which chlorophyll in the leaves uses sunlight to convert carbon dioxide into sugar and oxygen, thereby ripening the grapes.

Pretty close. But when it comes to winemaking, sugar is what you really need to know, since sugar helps with the next question.

2. What is fermentation?

The sugar made from all of that photosynthesis business is a pretty big part of not only the fermentation process, but your average Friday night, too. During fermentation, yeast eats sugar and creates alcohol, or more accurately, ethanol. But I’ll stay with alcohol since we’re talking about booze.

After the grapes are harvested and crushed, what you have is boring grape juice. In order to turn this juice into the wine you know and love, you have to either add yeast to it, or let yeast fall into the juice naturally. (I took a beer course where they talked about yeast falling into vats of beer naturally, too, in case you think that sounds ridiculous. In the old days, nobody even knew yeast caused fermentation. Hence, the original Bavarian beer laws only mandated 3 ingredients for beer: water, hops, and barley. Knowledge of yeast came later. There is literally yeast all around in the atmosphere, as well as in wine cellars, on the grapes themselves, so forth. Given the right circumstances and ingredients, fermentation will just, well, happen).

My line above about yeast “eating” sugar isn’t exactly right, by the way, but it gets the point across. Read this article for a good look at what really goes on. But the very basic point is Yeast + Sugar = Alcohol and Carbon Dioxide. The CO2 part is especially important when talking about sparkling wine.

Incidentally, you may wonder why the yeast doesn’t just turn the whole vat of juice into alcohol, or at least keep on going until all of the sugar is history. There’s two answers: 1) the winemaker doesn’t want this to happen. An effective way to stop the fermentation process is to simply lower the temperature of the wine. Fermentation stops. 2) if the winemaker lets the yeast go crazy on the sugar, fermentation will still stop after the wine reaches 15% alcohol, which makes the wine too toxic for the yeast. The yeast more or less generates enough alcohol to kill itself. Lightweight.

3. What is carbonic maceration?

Ever since I was a kid and aced a question on an exam even when I didn’t know what the answer was, I’ve been a fan of breaking the words down. This one looks to be about carbon, and if it’s about carbon, it’s probably about carbon dioxide. But what is maceration? That’s when the juice of crushed grapes is left to sit in the skins for a while in order to obtain colour, taste, tannins, so forth. Hmmm.

Carbonic maceration is a different way of fermenting the wine, and it’s associated with the Beaujolais wine region in Burgundy. The way it was explained to me is that grapes are harvested, then placed in a vat or vessel without first being crushed. Naturally, the grapes have weight, so the grapes at the bottom of the vat will be crushed no matter what. Still, the vast majority of the grapes are whole. The vat is a CO2 rich environment with CO2 pumped in. So there’s the carbon part. While fermentation on those crushed, bottom grapes’ juice continues as normal, fermentation for the rest of the grapes takes place through the skin of the uncrushed grapes. There’s the maceration part. The juice is sitting right in the skins.


The carbon dioxide gas permeates through the grape skins and begins to stimulate fermentation at an intracellular level. The entire process takes place inside each single, intact berry. Ethanol is produced as a by-product of this process but studies have shown that other unique chemical reactions take place that have a distinctive effect on the wine.

When something occurs at an “intracellular level,” you know it’s pretty cool. And kind of creepy.

4. What is malolactic fermentation?

We can break this one down, but unless you’ve studied some wine or chemistry, it might be tough. Anyway, to remember this one on a test, just remember the lactic acid part. Once you remember that, then you remember that there’s a malic acid in the universe. Therefore, malolactic.

Why does malic come before lactic? Who knows, but it might be because that’s the order of what happens in malolactic fermentation: You turn malic acid into lactic acid.

Lactic acid is softer on the palate than malic acid, which tastes sour and tart. A biproduct of the malolactic fermentation process is diacetyl, which can add a nice buttery taste to Chardonnay, too. In any case, malic acid is mostly used in red wine production. When making red wine, you leave the juice in the must (must is the mixture of juice, skins, seeds, and stems) for a lot longer than white wine, in order to impart taste and colour. However, this means more malic acid in the taste. To get rid of it, you use malolactic fermentation.

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