How Do You Make a Sauce That Is Sweet and Sharp at Once? Burn Sugar, Then Stop It

Sugar is heated in a pan until it melts and darkens to a deep amber, at which point vinegar is added, which stops the cooking violently and dissolves the caramel into a syrup. The result is intensely sour and sweet together, with a slight bitterness from the caramelisation that plain sugar and vinegar mixed cold would not have. It is a base rather than a finished sauce, usually reduced further with stock, fruit or wine and then mounted with butter or thickened, and a small quantity flavours a large amount of finished sauce.

Browning the sugar changes it chemically rather than merely colouring it:

• •Heat breaks sugar into hundreds of new compounds
• •Those carry bitter, nutty, fruity and buttery notes
• •Sweetness drops as the reaction proceeds
• •So the result tastes complex rather than merely sweet
• •Acid added hot dissolves it cleanly without crystallising
• •Going too far gives acrid burnt flavours that cannot be rescued

The preparation exists to solve a specific problem in savoury cooking, which is how to use fruit without producing something cloying. Rich meat, particularly duck, pork and game, benefits from sharpness and from sweetness together, and either on its own is unsatisfactory. The classical French duck with orange is built on exactly this base, and without it the dish is the sugary version that gave it a poor reputation. Cherry sauces for game, sharp accompaniments for pork and sweet and sour preparations across several cuisines use the same principle whether or not they use the name.

The base keeps far better than a finished sauce, which is what makes it useful in a working kitchen. A quantity made in advance holds for weeks refrigerated because sugar and acid together are hostile to spoilage, and a spoonful can be added to a pan sauce at the end to correct it. Cooks use it to rescue something that has come out flat, since it supplies acidity and sweetness and a little colour in one addition. The proportions are adjusted by reducing it further for sweetness or adding vinegar for sharpness, so one batch serves many purposes.

Cuisines that never met arrived at the same combination, which suggests the pairing is doing something fundamental rather than being a French invention. Chinese sweet and sour preparations combine sugar and vinegar over heat directly. Sicilian agrodolce does the same and is applied to vegetables as often as to meat. Persian cooking uses fruit molasses with sharp additions for the same balance. Medieval European cookery used sugar and verjuice together far more freely than later tradition did. What the technique here adds to the common idea is the caramel stage, which supplies the bitterness that keeps the result from tasting like confectionery.

Melting sugar to a deep amber and stopping it with vinegar gives a base that is sour, sweet and slightly bitter at once, because caramelisation breaks sugar into hundreds of compounds and reduces its sweetness. It exists to let fruit and sugar accompany rich meat without cloying. Sweet and sour cooking worldwide shares the idea, and the caramel stage is what keeps it savoury.