Tell someone you like sweet wine and you will often get a slightly pained look. Sweet has a bad reputation: cheap, cloying, a headache in a glass. And bad sweet wine earns it. But a great one is a different thing entirely, intensely sweet and, somehow, refreshing. The trick that separates the two has a name, and once you can taste it you will never judge a sweet wine by its sugar again. The trick is acidity.

Think about lemonade. Sugar alone is just cloying; add lemon and the whole thing comes alive, sweet and tart and refreshing at once. Wine works the same way. Sugar provides the sweetness, acid provides the lift. A sweet wine with low acid is flat and heavy, syrup. A sweet wine with high acid is balanced and bright, no matter how sweet it is. The sugar and the acid hold each other up.

Icewine is the clearest place on earth to taste this, because of how it is made. When the frozen grapes are pressed, the freeze concentrates everything left in the juice: not just the sugar, but the acid too, in the same proportion. So icewine arrives intensely sweet and racing with acid at the same time. That is why it tastes lifted instead of cloying, why a wine this sweet can still finish clean.

So here is the practice. Pour any sweet wine and pay attention to two moments. First, the sweetness as it hits: the honey, the fruit, the weight. Then wait, and notice what happens at the back end. Does the sweetness just sit there, flat and heavy? Or does a wave of acidity arrive and clean it away, leaving your mouth fresh and wanting another sip? That second moment, the lift, is the whole difference between a great sweet wine and a tired one. You are not tasting for sweetness. You are tasting for balance.

It is the same lesson that ran through the whole summer, just at the sweet extreme. Acidity is what made the off-dry Washington wine drinkable, what made the bone-dry Finger Lakes wine sing, and now it is what keeps the sweetest wine of all from collapsing into sugar. Acid is the spine of every white worth drinking, at any level of sweetness.

It is also the engine of this week’s pairings. A wine this sweet can still cut through rich custard and salty cheese, precisely because the acid is doing the cutting. More on Thursday.