24 May The chemistry of wine
Wine. It’s simply crushed and fermented grapes.Yep, that was me.
That’s the first line in our Crushed Grape Chronicles trailer that we put together….years ago. And it’s true…mostly. (whole berry ferments do happen, but eventually the weight of the grapes on the grapes causes them to be crushed.)
the chemistry of wine
So wine is made of 5 major components that go through some chemical changes, fermenting and such and create the tasty libation that we have all grown to love in all of it’s many forms.
5 major components of wine
Yes, there are other things you might find in your wine, but for the most part it’s these:
- Phenolic compounds
So wine’s a liquid, right? So as you would expect wine is a good portion (80-90%) good old H2O. This is mostly the water that came in the grapes (thank you mother nature), but upon occasion a winemaker might water down the initial grape juice or add water if the alcohol or phenolic compounds are too high for them.
This is one of the things we love about this beverage, the slight (or maybe not slight, depending on your style of drinking. We encourage moderation.) intoxication that comes with drinking it. That comes from the ethanol which is created in the alcoholic fermentation and is the main alcohol in wine (you will find glycerol, methanol and fusel alcohols in smaller amounts). The ethanol induces feelings of pleasure. As you drink, it is absorbed into your bloodstream and travels to the brain and relaxes you.
Of course too much…and you get drunk, which is rarely fun for the people around you.
Alcohol makes up 8 – 15% of the volume of wine. On the label you will see the abv (alcohol by volume). 8 % might be a cool climate white wine and 15% a warm climate red.
Ethanol is also a volatile compound, so it evaporates really easily and it helpful in getting all of those aromas to your nose.
Alcohol also with affect the “body” of a wine. You know how water and milk feel different in your mouth? Well higher alcohol takes the feeling in your mouth, closer to the milk end of the spectrum. You can see this when you swirl in big thick “legs” or “tears” running down the sides of the glass.
Acids make up just a bit of wine .5% to .75% by volume and there are two ways of measuring it.
- TA – Total Acidity: which is the total amount of acid by volume
- pH – the combined strength of the acids present
Keep in mind that some acids are stronger than others so TA is just the amount, and doesn’t give you the strength. So these are typically used together.
When you measure a wine’s pH keep in mind that the lower the pH, the stronger the acid. Wine typically lands between 2.9 and 3.9 on the pH scale, and a wine at 2.9 will be more acidic than a wine at 3.9.
More than one type of acid
There are 6 main acids that can be found in wine. Some of them are found in the grapes themselves and some are created during the fermentation process. A couple straddle that line.
- Tartaric acid – This is an acid found in both grapes and wine, and it is the most prevalent. It is the strongest acid in wine when you talk pH. If you have ever seen “wine diamonds” little crystals on a cork, that comes from this acid. While not a fault in a wine, winemakers can avoid these forming by using “cold stabalization” or cooling down the wine before bottling.
- Malic Acid – This is a grape acid. It’s sharp taste is like that of green apples. This acid decreases as grapes ripen, so cool climate white grapes and underripe grapes will have high levels of this acid. (Later we will discuss malolactic fermentation, which is used to lower the malic acid in a wine)
- Citric Acid – Yes the acid that you find in citrus fruit. It’s not normally thought of in grapes because the quantities are so small that you can only find it with super specialized fancy equipment. However…sometimes it’s added to pump up the TA in a wine (just not in good wine).
- Lactic Acid – You don’t find this acid in the grapes, but…remember I mentioned malolactic fermentation? Well…lactic acid bacteria munch on the malic acid and turn it into lactic acid, which is smoother, rounder and less acidic. This malolactic fermentation can be on purpose or not, but it is often used by winemakers to soften a wine. You also might get a buttery aroma and a creamy texture (think some chardonnays)
Acetic Acid – You will recognize this acid from vinegar (well, most vinegars). This is a fermentation acid, so you won’t find it in grapes on the vine. It can contribute to a wine’s bouquet as it evaporates quickly, but sometimes there is another pesky bacteria, this time acetobacter that can cause a reaction between the ethonol and oxygen that can ruin a wine.
- Succinic Acid – This guy can be found in grapes and can also be created during fermentation. It’s found in small quantities in either case and is sharp as well as slightly both bitter and salty.
One of the measurements winemakers take to determine if a grape is ready to harvest is measuring it’s brix or sugar levels. Typically this will be 15% to 28%.
There are two main sugars that you find in grapes
These are both monosaccharides or simple sugars and are, lucky for us, highly fermentable! Those beautiful yeasts convert the sugar to ethanol. If they finish the job, eating up all the sugar, you get a dry wine. If not, you get a little residual sugar, leaving a little sugar in the wine and thus, a little sweetness. Typical detection of sweetness in a wine is at 1% rs, but some people can detect is at lower levels up to .5%.
In some cases, the winemaker might want a little sugar left in the wine to perhaps balance a high acid level. In some cases they are looking to make a sweet wine and in that case they can leave up to 24% rs in the wine (think late harvests, ice wines or Sauternes). Sometimes…in less lovely wines, the sugar might be there to cover up a sucky wine. We are suckers for sugar.
Okay, here’s where the real flavor comes in. Phenolic compounds come mostly from the skins and seeds and stems in the wine. They are also accountable for the color in a wine. These molecules are wide and varied and might be small compared to the other components, but they have a large impact on the taste, smell and texture of a wine.
- Anthocyanins – Say that one 3 times fast! These guys give red wine it’s color, from red to purple to blue. Acids do play into this also, the higher the acid, the redder the wine, the lower the more blue.
- Flavonols – Here’s where white wines get there golden tones. They increase with sun and ripeness. Hence, a wine that is very pale, is likely either from a cooler climate or less ripe, while a golden yellow color might indicate more flavonols (I really love that word) and might be from a warmer, sunny climate and have been more ripe at harvest.
- Resveratrol – Okay another tricky pronouciation. This compound is thought to have health benefits. You’ve seen those posts on facebook about how red wine is good for you. Well…many studies have attributed this compound to anti-aging, cancer-fighting and disease prevention. (again…remember, all things in moderation)
- Tannins – When it comes to phenolic compounds, this is probably the one you have heard of. They, like the others are found in the skin, seeds and stems of grapes, but you can also find them in oak. These are the bitter compounds you taste when you bite into a grape seed. They will dry your teeth if you swish them in your mouth, that’s astringency. They have a natural preservative that protects wines from oxidizing. Think about cabernet, a young one is sometimes so bitter and astringent that you almost can’t drink it. But…it can age a long time and gradually round. That’s those hard working tannins that cabernet is full of. This is also a reason for aging in oak barrels as the barrels themselves can help prevent the wine from oxidizing.
- Vanillin – sound like vanilla right? Yep, vanillin is found in vanilla beans and in oak. That’s why you get that vanilla scent in wines or whiskeys aged in oak barrels!
You can get sediment from phenolic compounds. So you buy a nice bottle of red wine and cellar it for a while (quite a while). You go back and pull it from the cellar and notice, that it looks lighter in color and that you have sediment in the bottom. This is the tannins and pigments (which are phenolics) that have polymerized (they combine into longer molecule chains and get too heavy) and dropped out of the liquid to settle at the bottom of the bottle. With a cabernet again, this is good, it will mean the wine will be less astringent.
There’s more in there. We are just going to talk about a few.
- Aldehydes – When wine is exposed to air the oxidation produces aldehydes. Sometimes you want that, like when you are making Sherry or Madeira, but most of the time you don’t. If you have ever left a bottle in the heat or just on the counter open too long and come back to find it undrinkable, that would be aldehydes.
- Dissolved Gases – CO2 in a sparkling wine is a clear example. You might see that in small quantities in a Pet Nat or even in other wines. It will make a wine feel fresh and helps to release the aromas. There are always dissolved gases in a wine, just often not in big enough quantities to notice. We talked above about oxidation, that would be dissolved oxygen. It’s the reason that winemakers add sulfur to wines. Sulfur absorbs those free roaming oxygen molecules to keep the wine from oxidizing.
- Esters – They create all those wonderful smells in wine. Odiferous compounds that are the result of a little coupling of an acid and an alcohol. Most of the time we like these odors, but at high concentrations, they might not be as pleasant. Take ethyl alcohol, a little bit smells fruity and flowery, truly lovely, but high quantities smell like nail polish remover.
- Sulfites – Small bits of sulfur are produced during fermentation, but just small bits. But remember I said that they protect a wine from oxidizing? Sulfur is widely used by winemakers out of necessity to protect wines from oxidation. Deal is, some people are really sensitive to sulfurs (not nearly as many as think they are, but a significant enough amount). As a result, here in the US wines with more than 10 parts per million of sulfur dioxide, must be labeled “Contains Sulfites”.
We will be continuing our series of educational posts on wine in all it’s complexity! Join us to explore and learn more about this fantastic and fascinating liquid.