All you really need to make fish sauce is fish, salt, and time. Many labels will also state that it contains water, which is actually the liquid that is naturally released from the fish as they ferment. Lower-grade fish sauce also tends to contain added sugars, and it’s best to avoid these as well. You will have more control over the sweetness of a dish by adding your own sugars during the cooking process.

Higher quality fish sauce will also state a number on their label followed by the letter “N”. This is to indicate the nitrogen levels within, and the higher the number, the better. According to South China Morning Post, high-grade fish sauce is anything above 30N and most fish sauce on the market is around the mid-20N range.

Another thing to look for on the label is if it mentions which pressing the fish sauce is taken from. Much like pressing oil, the first press is the purest, followed by less and less flavorful pressings that are topped up with more and more salt.