Sweet and sour sauces showcase the dynamic of the sugar-food acid relationship at its best. Every sweet or fatty ingredient works well with acid: The plucky white wine-spiked plum sauce that accompanies foie gras, the lemon curd spread over a warm tart, and the familiar sweet and sour sauce served with the eponymous chicken preparation all rely on flavor balance -- a sweet-sour stasis, almost -- to work. All sweet and sour sauces are simple: Mix a base of equal parts sugar and acid and flavor it to taste.
The orange-red sweet and sour sauce ubiquitous to breaded chicken nuggets and American Chinese restaurants uses ketchup for body. Authentic sweet and sour sauce -- the one that resembles the Western variant closest -- likely has its origins in Cantonese cuisine, but each region in China -- Sichuan and Hunan, for example -- has its own interpretation made with regional ingredients. The sauce gets its characteristic glossiness from cornstarch.
Add 1 part brown sugar, 1 part rice vinegar and 3 parts ketchup to a heavy-bottomed saucepan and simmer it for about 5 minutes. Add pineapple juice to taste and thicken the sauce with 1 tablespoon of cornstarch slurry per cup.
Gastrique -- a sugar-acid reduction -- sits at the nexus of sauce and syrup, glaze and gravy. Thick but not fluid like a traditional sauce or gravy, sticky but not as sweet as a glaze or syrup, gastriques combine a few qualities from each. Gastriques consist of a reduced acid-sugar base and a secondary flavoring ingredient. The gastrique base delivers the primary flavor, so use a robust, tasty vinegar -- fruit-infused vinegars are a natural fit.
Add sugar to a heavy-bottomed saucepan and cook it over medium-high heat until caramelized, stirring occasionally. Add an equal amount of flavored vinegar quickly to the caramelized sugar and stir. Stir in the secondary flavoring ingredient, such as herbs, pan juices or brandy, and cook the gastrique for another minute or two.
Sweet and sour dessert sauces often contain the same ingredients as gastriques but aren't as intense. The difference is reduction -- instead of reducing, dessert glazes thicken with a cornstarch slurry, which gives them viscosity and a glossy sheen. You can use fresh fruit juice or fruit packed in syrup.
Add 1 part sugar and 2 parts juice to a heavy-bottomed saucepan. If using fruit packed in syrup, strain the syrup through a sieve, pressing on the fruit as you do; add sugar to the syrup to taste. Stir in acid -- citris juice or fruit vinegar -- and secondary ingredients, such as spices, liquor or additional juice, to taste. Add 1 tablespoon of cornstarch slurry per cup of sauce and simmer it for 5 minutes.
Gastriques and dessert glazes lend themselves well to oaky liquors and wine, such as barrel-aged bourbon, brandy and chardonnay. Add an equal amount of spirit as vinegar to the sugar when making the gastrique; add the spirit to taste to dessert glaze before you thicken it. Chutneys and jams make worthy sweet and sour sauces; cook chopped fruit down with an equal amount of sugar and vinegar. Chinese-style sweet and sour sauce has room for most pungent and aromatic ingredients. Saute minced onions, green onions, garlic or ginger until soft but not browned, and add them to the sauce as it simmers.