2. Sweetness and Acidity

Last time you learned to look at a wine and smell it before it ever touched your lips. Now the wine goes into your mouth. Your nose can tell you a lot about fruit and flowers and earth. It cannot tell you how much sugar is in the glass, or how sour the wine is. Only your mouth can do that. This lesson is about those two things, sweetness and acidity. They work as a pair, and each one pulls against the other. How they settle against each other is your first look at what tasters call a wine's structure.

How sweetness and acidity work in your mouth

Start with sweetness, because you already know half of it. In the first lesson you learned that yeast eats the sugar in grape juice and turns it into alcohol. If the yeast eats all of it, the wine is dry. If some sugar is left over, that leftover has a name. It is called residual sugar. "Residual" just means what remains. So residual sugar is the grape sugar the yeast did not get to, still sitting in the finished wine.

Residual sugar is measured in grams per liter. A liter is a bit more than a standard bottle. So a wine with five grams per liter has about five grams of sugar in every liter. That is roughly a teaspoon or so of sugar spread through a whole bottle and then some. That helps explain why small amounts are hard to notice.

Here is how much it takes for people to notice. Most tasters cannot pick up any sweetness below about two to four grams per liter. Trained tasters can sometimes find it at one or two. Ordinary drinkers often do not reliably notice sweetness until it reaches somewhere between five and ten grams per liter. That is especially true when the wine is fairly sour, for reasons you will see in a minute.

Tasters sort sweetness on a simple scale with four steps: dry, off-dry, medium and sweet. Here is roughly where each step falls for still wine, the kind without bubbles, using the scale taught by the Wine and Spirit Education Trust and the European Union's rules. A dry wine has up to about four grams per liter. Off-dry means just a touch sweet, from about four up to about twelve. Medium, sometimes called medium-sweet, runs from about twelve up to about forty-five. Sweet means more than that. The very sweet dessert wines from late-picked grapes, from grapes with noble rot, or from frozen grapes often carry a hundred to a hundred and fifty grams or more.

Those borders are not walls. The rules bend them for sour wines. Under European rules, a wine can still be called dry with up to nine grams per liter if it is sour enough to balance that sugar. An off-dry wine can stretch to eighteen if its acid is high. The rule bends because sourness hides sugar. A number on a lab sheet is not the same as what your tongue feels.

So how do you judge sweetness in the glass? Take a small sip. Let it cover your tongue. Sweetness shows up quickly, often at the front and tip of the tongue, as a soft, rounded feeling. Ask yourself one plain question: is there any sugar here, or none at all? If you feel nothing sweet, call it dry. If you feel a faint hint, call it off-dry. Then move up the scale from there.

Now the trap. Many dry wines seem sweet. There are two reasons, and neither one is sugar.

The first reason is fruit aroma. A wine that smells of ripe peaches, ripe strawberries or jam makes your brain expect sugar. Your brain has learned that ripe fruit is sweet. When the smell arrives, it fills in a sweetness that is not there. The smell is real. The sugar is not.

The second reason is alcohol. Alcohol has a slight sweetish taste of its own, and it gives a warm, full feeling. A dry wine high in alcohol can feel richer and rounder, and that roundness reads as sweet.

Here is how to tell the difference. Fruitiness is something you smell. Sweetness is something you taste. Try pinching your nose shut while you hold a sip in your mouth. With the nose closed, most of the fruit vanishes, because most of what we call flavor is really smell. Whatever sweetness is left is actual sugar. If the wine goes flat and plain with your nose pinched, the sweetness you thought you had was fruit. The habit to build is to say "fruity but dry" when that is what you find. It is a normal, common description, and it is often correct.

Now acidity. Every wine is sour to some degree. That sourness comes from acids, and the main ones come straight from the grape.

The strongest and most plentiful acid in grapes is tartaric acid. It is steady. It holds up well through fermentation, and it does most of the work of giving wine its crisp, tart backbone. The second acid is malic acid. Malic acid has the sharp sourness of a green apple. In fact the name comes from the Latin word for apple. As grapes ripen on the vine, their malic acid slowly drops. There is a little citric acid too, the acid in lemons, but grapes carry only a tiny amount. Fermentation also adds a few acids of its own in small amounts, but tartaric and malic are the two that matter most, and both come from the fruit.

There is one more step worth knowing now, because you will hear about it in the cellar lessons later. In many wines, helpful bacteria turn the sharp malic acid into a softer acid called lactic acid, the same acid found in milk and yogurt. This is called malolactic conversion. The wine ends up less tart. For now, just know that a winemaker can choose to soften a wine's acid this way.

How does acidity feel? Mostly, it makes your mouth water. Sour things set off your salivary glands. You know the feeling from biting into a lemon. Wine does the same thing, only more gently. A wine with more acid makes your mouth water more, and for longer. You may also feel a light prickle or tingle along the sides of your tongue.

To judge acidity, take a sip, then swallow or spit. Spitting is normal practice, and it works just as well here. Then wait a few seconds and pay attention. How much is your mouth watering? How long does it last? A little water that fades fast means low acidity. A clear rush of water that lingers means high acidity. Something in between is medium. So acidity is rated on three steps: low, medium and high.

Two more words belong here. A wine with lively, high acidity is often called crisp. A wine with too little acid is often called flabby. Flabby is not a kind word. It means the wine feels soft and loose in the mouth, as if nothing is holding it up.

This mouthwatering test has a useful feature. Your salivary glands react to the acid whether or not there is sugar in the wine. Your brain may not notice the sourness up front, but your glands still respond. So even in a sweet wine, where the sourness is hidden, you can find the acid by waiting and noticing how much your mouth waters afterward.

Now put the two together. This is the center of the lesson. Sweetness and acidity hide each other. Sugar softens how sour a wine seems. Acid hides how sweet it seems.

You can see this without any wine at all. Think about lemonade. Lemon juice and water alone is harsh. It makes you wince. Stir in sugar, and the lemonade gets pleasant. The lemon did not leave. The acid is all still there. The sugar just covers it up. Now keep adding sugar, past the point where it tastes good. It turns syrupy. It coats your mouth and feels heavy. Go back the other way, and add more lemon to an overly sweet glass. It comes alive again. The sugar is still all there, but the sourness cuts through it.

Wine works the same way. Take a wine with about ten grams per liter of residual sugar. In a wine with low acidity, ten grams tastes plainly sweet. In a wine with high acidity, that same ten grams can taste completely dry. Tasters point to Riesling from Germany's Mosel region and to Champagne as examples. Both can carry noticeable sugar and still taste crisp, because their acid is high enough to hide it.

That is why you judge sweetness and acidity separately, and then judge how they sit together. That last judgment is called balance. A wine is balanced when neither one takes over. A sweet wine with too little acid tastes flat and cloying, like the syrupy lemonade. The same sweetness with enough acid tastes fresh and clean, and leaves you wanting another sip. A very sour wine with no sugar can still be balanced, if its fruit and body are strong enough to carry the acid. But hold that thought, because body is a later lesson.

Balance is your first real idea of structure. Structure means the parts of a wine you feel in your mouth, the things that give it shape. Sugar and acid are the first two parts. More parts are coming. When you can say "off-dry, high acidity, balanced" about a wine, you are describing what the wine is, not just whether you like it. That is the skill this whole tasting unit is building.

Acidity matters later for two more reasons. It helps a wine age, and it shapes how a wine works with food. Each of those gets its own lesson. For now, all you need is the feeling in the mouth.

If you want to try this, here is an easy exercise. It is optional. You can follow the course without drinking anything. You need two white wines. One should be dry, such as a Sauvignon blanc or an unoaked Pinot gris. The other should be off-dry. Many Rieslings from Germany or Washington are off-dry, and labels often say so on the back. Pour a small amount of each, about fifty milliliters, the same as in the last lesson. Keep water and a cup for spitting nearby.

1. Taste the dry wine first, and decide whether you feel any sugar at all.
2. Then pinch your nose, take another sip, and notice what fruit drops away.
3. Swallow or spit, wait a few seconds, and rate the acidity as low, medium or high by how much your mouth waters.
4. Repeat all three steps with the off-dry wine, and then ask whether its sugar or its acid seems to take over, or whether they hold each other even.

Do not worry about getting it right. The point is to notice that sugar and acid are two different feelings, and that one changes how you feel the other.

Why Willamette grapes keep their acid

Now bring this home. You already know the valley is cool, and that Pacific air through gaps in the Coast Range, especially the Van Duzer Corridor, holds back summer heat. Here is what that cool air does to the two acids you just met.

The 45th parallel runs through the valley, which stretches from about forty-three and three quarters to forty-five and three quarters degrees north. By the measure growers use for heat over a season, it falls in the coolest class, often called Region One. Summer afternoons are warm, around the high seventies to about eighty degrees Fahrenheit. Nights drop to around fifty to fifty-three. That swing is often twenty-five to thirty-five degrees a day, and more than forty in some high, exposed vineyards. Through the Van Duzer Corridor, cool ocean air pulls in most afternoons, often with winds of fifteen to twenty-five miles an hour or more, cooling the vines quickly.

Remember that tartaric acid is steady. Through ripening it mostly stays put, thinning a little as the berries swell with water. Malic acid is different. The grape burns it off as fuel while it ripens, and it burns it fastest in heat, above about eighty-six degrees. Cool afternoons and cold nights slow that burning way down. So grapes in the valley hold on to more of their malic acid. Cooler weather also slows the build-up of sugar, so the grapes have time to develop flavor without piling up as much sugar, which would become alcohol.

That is why growers, winemakers and critics so often describe Willamette Pinot noir, Pinot gris and Chardonnay as fresh or bright. It is not that every wine is the same. The climate tends to hand winemakers grapes with acid to spare. For Chardonnay, that matters because most Oregon Chardonnay goes through full or partial malolactic conversion, which softens the acid. Starting high keeps it from going flabby afterward. Pinot gris is usually made without that conversion, so its natural acid has to balance its rich, slightly oily feel.

This sets up the picking decision. As grapes hang, sugar climbs and acid falls. Pick early and you keep more acid but less sugar, which means less alcohol and maybe less ripe flavor. Pick late and you get more sugar and ripeness but lose acid. Winemakers measure sugar in a unit called degrees Brix, and they test acid and taste the fruit, chewing seeds to see if they have turned from green to brown. In the valley there is another pressure. Autumn rain arrives from the Pacific, and it can split berries, water down juice and bring rot. So picking is a race between ripeness and weather.

Oregon State University's extension service and the Willamette Valley Wine Association give rough picking targets that show the trade. Still Pinot noir is often picked at about twenty-two to twenty-four and a half degrees Brix, which makes wine of about thirteen to fourteen percent alcohol. Grapes for sparkling wine come in much earlier, around eighteen and a half to twenty and a half degrees Brix. That keeps their alcohol low and their acid sharp, because bubbles need that sour edge.

Where the 2026 harvest stands

That trade between sugar and acid is playing out right now, in mid-October 2026. Here is where this year's harvest stood, according to reports from early to mid October.

Picking started in late August and early September, with fruit for sparkling wine and the earliest sites. That matches what you just learned: the grapes meant for bubbles come in first, while their acid is still high. Still Pinot noir and Chardonnay began coming in around September eighth, with Durant Vineyards in the Dundee Hills among the early ones. Others followed through the month, Hyland Vineyard on September eighteenth and Latchkey Vineyard on September twenty-second. By early to mid October, harvest was described as in full swing and wrapping up across the valley's appellations, with Winter's Hill and Lachini among those finishing their Pinot noir.

The season behind it was gentle. Spring was warm, with sun and rain in short bursts, and budbreak came early. Summer stayed moderate, with days in the eighties and nights in the forties to mid fifties. Most importantly, there were no long heat waves. That fits the acid story directly. Without strong heat, the grapes kept burning malic acid slowly, ripening steadily while holding their freshness. A dry summer also kept mildew and rot low, and no damaging frost was reported.

There was one scare. Smoke from the Grasshopper Fire, burning roughly sixty-five miles southeast of Mount Hood, reached the valley around August fifth. Smoke can leave an ashy fault in wine, which this course will cover in its own lesson. Elizabeth Tomasino, an enology researcher at Oregon State University, and vineyard managers described it as old smoke that had traveled far enough to lose most of its risk. Testing showed little threat of smoke taint.

Growers reported clean, tight clusters with small berries and concentrated juice. Final tonnage is not counted yet. The year also comes after a hard 2025 for the industry, when Oregon grape production fell twenty-five percent and sales fell sixteen percent, so some growers farmed less or left unsold blocks unpicked. Early opinions are hopeful. Winemakers, including Katie Santora of Chehalem Winery, have called 2026 potentially phenomenal, pointing to clean fruit and bright acid. Those are early words from people in the industry, said before the wine is even finished. The wines themselves will show whether they hold up.

Next lesson, the palate keeps going: tannin, alcohol, body and finish, the rest of what you feel when a wine is in your mouth. Until then, the next time you drink something sweet and sour, a glass of lemonade, a soda, an apple, stop for a second and notice which one wins, the sugar or the sour. That small habit is the start of tasting structure.