Soy sauce is to Asian recipes what salt is to Western ones. It is a basic ingredient that is generally made from fermented soy beans, water and salt.
There are many different styles to suit different tastes and cuisines. Classic Chinese recipes, for example, favour a light soy while Japanese dishes often incorporate Shoyu for an intense umami flavour.
There are huge differences in the quality of soy sauces as well. Good soy sauce can be identified by "naturally brewed" or similar wording. Some brands take short-cuts by using chemicals and various additives to make up for the lack of flavour and colour, but these do not compare with the real thing.
Types of soy sauce
LIGHT SOY SAUCE: Also known as Chinese soy, light soy sauce has a lighter colour, is thinner in consistency and very salty. It is generally used as seasoning during cooking.
DARK SOY SAUCE: This sauce is more common in South-East Asia and has caramel added to it, making it darker and more flavourful. It is used as a table condiment, in dipping sauces and for marinating.
JAPANESE SOY SAUCE: Also known as Shoyu, the Japanese variety is comprised of wheat in addition to soy beans, water and salt. It is milder and adds a full-bodied flavour known as "umami" to dishes.
TAMARI: This sauce is a thick Japanese-style soy sauce made from soy beans and rice. It is usually gluten-free, though those with a wheat intolerance should still check the label. It is less salty than other soy sauces, making it ideal for dipping sauces (especially for sushi).
KECAP MANIS: Hailing from Indonesia, this soy sauce has a thick and rich texture.
Oyster sauce is made from fermented oyster extract and has a rich and savoury flavour with a caramel note.
As with soy, there are good and poor oyster sauces, and the quality greatly affects the flavour. Premium versions have a high percentage of oyster extract, while lower quality sauces use artificial flavouring.
Price is generally a good indicator of quality and it's been touted as a great way to lower your salt intake.
Fish sauce is used by South-East Asian cooks as a universal seasoning in the same way as soy sauce is used by Chinese and Japanese cooks.
Some people find the smell of the sauce itself to have an unappealing pungency, but when it meets other ingredients it becomes a wonderful seasoning and flavour enhancer.