Of all the hundreds of Chinese bean paste sauces, hoi sin is perhaps the most famous and widely traveled.
It is made from fermented yellow beans that are seasoned with rice vinegar, sugar, salt, chilli, garlic and sesame oil. Flour is added as a thickening agent and the resultant "sauce" is more closely akin to a paste in consistency. Many versions also contain red food colouring, meaning hoi sin can vary in colour anywhere between deep brown to almost black.
The Mandarin word, haixian and the Cantonese hoisin both translate as sea-delicious, which is a little odd, as there is no seafood products in the sauce, and due to its pungent flavour is rarely used in fish dishes. The Szechwan term for this sauce is yuxiang, or fish-flavour, further compounding the issue. Perhaps the lingeringly complex salty flavour is comparable to salt water flavours. Although the Cantonese name is hoisin, the sauce is often sold in the west as "hoi sin", but they are exactly the same product.
Hoi sin is an extremely versatile sauce, finding a place in not only the Chinese kitchen, but as a table condiment as well. One of the common names for hoi sin is barbecue sauce, due to the inclusion of hoi sin in many Chinese BBQ marinades. Hoi sin sauce can also be used sparingly in stir fries, as not only a flavour enhancer but a thickening agent as well. Many Chinese BBQ dishes arrive at the table with a small bowl of hoi sin for dipping. The world famous dish, Peking duck uses a special sauce in its first course, wrapped up inside a mandarin pancake. This sauce, Tian Mian Jiang is virtually unknown outside of China, so hoi sin is often used as an incorrect, but tasty alternative.
The flavour of hoi sin is unmistakably pungent. Its beauty lies with the seamless harmony in which the separate flavour elements are brought together. Pungent garlic, the slow sting of chilli, a tantalizing background sweetness, all layered upon the deep mysterious flavour of the yellow bean base. As with many Asian condiments, quality varies markedly between manufacturers. Try to purchase a hoi sin sauce made in Mainland China or Taiwan. I have found the Lee Kum Kee brand to be particularly reliable.