It\u2019s hard to pinpoint when popular opinion declared that good wines must be dry, but it couldn\u2019t be farther from the truth. Whether it was the recent ros\u00e9 revival that taught us to value dryness in response to the bulk blush wine of a bygone era, or bad experiences with cheap, sweet alcohol, most aficionados today choose dry wines.\r\n\r\nHowever, sweet wines are made from some of the most regulated, carefully observed grapes, and they represent terroir and tradition as fiercely as any dry offering.\r\n\r\nConsider the rigorous German Pr\u00e4dikatswein system, which ranks top grapes from specific regions based on their ripeness at harvest. Or there\u2019s the serious manner by which a Port producer assesses the year\u2019s conditions and the resulting young wine before it declares a vintage. The prediction determines if a given bottling is worth decades of guarding, and at stake is nothing less than the producer\u2019s reputation.\r\n\r\nAn artfully made sweet wine is a labor-consuming effort with risk at every turn.\r\n\r\n\r\nWhen is a wine sweet?\r\nWhether a wine is \u201csweet\u201d isn\u2019t such a straightforward question. But a glance at the alcohol by volume (abv) can provide a clue.\r\n\r\nMany dry wines register at more than 14% abv, while finding alcohol below 10% on a bottle generally indicates a sweet wine, as is common with Kabinett Riesling or Moscato d\u2019Asti. Although the category of \u201cdessert wine\u201d persists on wine lists and elsewhere, understanding which are technically sweet, and to what degree, is critical to understanding and appreciating them.\r\nHow sweetness in wine is measured \r\nThe sweetness of a wine is spoken about in terms of residual sugar, measured in grams of sugar per liter that remain in the finished wine. Wines considered dry have no perceptible residual sugar, and are typically fermented to 0\u20133 grams per liter, though many wines that pass as dry can contain even up to 8\u201310 grams, or about 2 \u00bd teaspoons, per liter. The perception of sweetness varies depending on a number of factors, from the grapes\u2019 natural acid to winemaker technique.\r\n\r\nIn addition to the taste on our palate, the presence of sugar adds perceptible weight to the wine and changes its texture. This can manifest as a touch of voluptuousness, in the case of a still Vouvray or Rh\u00f4ne white, or the dense syrup of aged Pedro Xim\u00e9nez.\r\n\r\nTo leave some residual sugar in a wine also balances high-acid grapes, a surprisingly common technique, but these wines are still classified as dry. Though there\u2019s no obligation to, most producers will indicate on the label if the product veers into the vague territory of off-dry, or slightly sweet, wine. In a sparkling wine, this can be labeled \u201cextra-dry,\u201d to the confusion of many.\r\n\r\nSweet wines are best made from grapes with a high acid content. Acid structures what otherwise can be a bland sweetness, while residual sugar makes acidic flavors and aromas more palatable.\r\n\r\nEven in the sweetest wines, the role of acid cannot be overemphasized.\r\n\r\n\r\nWhat are the different types of sweet wine?\r\nHow a wine was made can predict the sweetness of the final bottling. Sweet wines are either fermented directly from grapes with concentrated juice, like with late-harvest wines, or by halting an ongoing fermentation with alcohol, temperature or sulfites, or in some cases, adding a sweeting agent after fermentation. They can be made from any variety in a location suitable for growing.\r\nLate-harvest grapes\r\nUnfortified wines, sometimes called \u201cnaturally sweet,\u201d come from grapes that have been concentrated in some way. This could mean grapes harvested late in the season, a style common to cooler climates. It can also be achieved from a period of drying after harvest, or inoculating the fruit with fungus like Botrytis cinerea, a k a \u201cnoble rot.\u201d\r\n\r\nWhatever the technique, the goal is to reduce water content, which amplifies the grape\u2019s remaining sugar, acid and flavor. The more water you let dry out, the more intense the wine.\r\n\r\n\r\nPassito\r\nSome grapes are picked at harvest time, but left to dry, typically on mats, from a few weeks to a few months. This ensures high acidity and supervised drying. In Italy, this style of winemaking is called passito. It\u2019s used to make both dry and sweet Amarone as well as Vin Santo, the sweet wine most associated with the country.\r\n\r\nOther styles simply demand waiting until all berries on the vine resemble raisins at which point they\u2019re picked meticulously by hand and pressed.\r\n\r\nWaiting for grapes to get to this state is tricky. If rain and hail aren\u2019t a threat, there\u2019s always the risk of unfriendly rot, or even birds that will eat your crop. In wineries where sweet wine is not the lone style produced, vintners often must weigh potential losses when they decide whether to create a sweet or dry wine.\r\n\r\nWhen sugar levels get too high, it also inhibits the yeast. In basic fermentation, yeast consume sugar to produce alcohol and carbon dioxide. When there\u2019s too much sugar, the yeast become overnourished and can\u2019t do their job, creating another potential risk when producing wines in this style.\r\n\r\n\r\nBotrytized wines\r\nWines made from grapes infected by noble rot, or\u00a0Botrytis cinerea, are among the most famous and expensive in the world. This method was said to be first practiced in the Tokaj region of Hungary before it spread to Germany and France, though it\u2019s limited to regions where the climate and fog can trigger the rot.\r\n\r\n\r\n\r\nThese wines can only be made during the best vintages, and noble rot is not always guaranteed to take hold on the crop.\r\n\r\n\r\nIce wine\r\nIce wine is a method where grapes are picked when the weather becomes cold enough for them to freeze. The grapes must also be pressed while frozen. This yields a more concentrated juice by leaving much of the water behind, still frozen in the grape. This method originated in Germany, where it\u2019s called eiswein. It\u2019s also become particularly popular in Ontario, where it\u2019s trademarked as icewine, generally made from Riesling, Vidal Blanc and even a unique red variation based on Cabernet Franc.\r\nFortified sweet wine\r\nSince yeast dies at alcohol levels greater than 18%, fortifying a wine to that degree or higher is an effective way to stop fermentation and retain any leftover sugar. Wines like Port, Madeira, and France\u2019s vin doux naturel (VDN) are all produced this way. An entry-level bottle produced in this style costs less typically than a naturally sweet wine.\r\n\r\nOne technique to create fortified wine is by using a mutage, or unfermented grape juice blended with a neutral spirit, and mixing it with the fermenting wine in order to raise alcohol levels and stop the yeast. Mutage can even be consumed on its own, often with brandy being used as a base, more commonly called mistelle. While not technically a wine, mistelle can have similar aging potential and drink like a fortified wine.\r\n\r\n\r\nHow long can sweet wines age?\r\nSweet and fortified wines are some of the safest bets for long-term aging. Produced with an emphasis on acidity and added preservation power in the form of high sugar and sometimes alcohol, these wines are famous for their longevity.\r\n\r\nVintage Port is meant to be aged for at least 15 years, although multiple decades are preferred. The same applies to quality Madeira, the cooked wine said to last forever. Tokaj and Sauternes are unfortified wines that can be aged for decades, which has led to record-breaking prices at auction for antique bottles.\r\n\r\nAs these bottles age, the sweetness does not disappear, but the wine picks up darker flavors. It strikes a better balance on what may have tasted like simple sugar when the wine was young.\r\n\r\n\r\nServing sweet wines\r\nWhen serving guests, lightly sweet wines like a Halbtrocken Riesling or Amabile Lambrusco will generally be consumed quickly, like dry wines. However, most people tend to sip sweeter options slower, so consider the appropriate serving size with a very sweet wine. Many serious sweet wines come in half-bottles that befit their concentrated contents.\r\n\r\nSweet wines can be served in regular wine glasses, especially if you only enjoy them occasionally. However, decorative miniature glasses should be avoided, as they inhibit the swirling and smelling that are a valued part of appreciating these wines. If you want a dedicated vessel for fortified wines, a Port glass, with its short, tulip-shaped bowl, is useful to reduce exposure to alcohol vapors and concentrating aroma.\r\n\r\nAll sweet wines should be lightly chilled. It tempers the perception of sugar, but doesn\u2019t obstruct delicate flavors.\r\n\r\nWith so many styles and variables, from the way a wine was made to its grapes and age, it\u2019s clear that sweet wines are no less complex than the dry ones that receive most of the public\u2019s attention. Those curious enough to discover them will be rewarded with a slew of new and unique flavors and textures, all made possible thanks to sweetness.