In Indonesian, kecap is a term that simply means “fermented sauce,” but it has come to be used specifically to refer to soy sauce. There are two major styles of Indonesian soy sauce, kecap manis and kecap asin. Both are widely available from Asian markets, and they are certainly worth experimenting with, because they have unique flavors that are designed to complement Indonesian food to perfection.
Like other soy sauces, kecap is made by fermenting soybeans with salt and other ingredients to create a distinctively flavored liquid. It is, incidentally, is probably the fermented sauce which inspired the flavor and name of ketchup; early forms of ketchup were made with an assortment of fermented ingredients, rather than tomatoes. It can be sprinkled onto foods or added to food as it cooks to bring out a desired flavor.
Kecap asin is a salty soy sauce with a relatively mild flavor. If a recipe calls for this soy sauce and a cook has trouble finding it, he or she can use Japanese usukuchi shoyu or an ordinary light soy sauce. Because it is naturally very salty, cooks should go easy on the salt when they include this sauce in a dish to ensure that they do not overwhelm their diners with saltiness. Kecap asin can also take a moment to fully develop its flavor in a dish; the best practice is to add a small amount, allow the dish to sit for a moment, taste, and adjust the flavor as needed.
Kecap manis is a truly unique form of soy sauce. It is made with the addition of palm sugar, which adds a very sweet flavor that makes the sauce taste kind of like molasses. It also looks like molasses; it is extremely thick and dark. Other ingredients like star anise and garlic are sometimes added to enhance the flavor; in a situation where a cook needs this version and cannot find any, he or she can try giving molasses mixed with dark soy sauce a shot.
Indonesian cuisine has a number of fermented ingredients, much like cuisine from other regions of Asia. When handled well, these ingredients can keep for an extended period of time, making them ideal in warm, humid climates. Many cultures have also developed a taste for fermented foods ranging from kimchi to kecap asin, and it is possible to find unique regional dishes which showcase these ingredients. When someone tastes an Indonesian dish and have trouble identifying the flavor, it might be kecap; people can ask the cook, as cooks are often happy to share ingredients with curious diners.