Tom Yum paste is a mixture of aromatic herbs, spices, and seasonings made into a paste to be added to the stock when making the tom yum soup. You can make this paste at home from scratch or buy it from Asian stores. The tom yum paste is usually bright red and contains ingredients like Thai red chiles, lemongrass, galangal, kaffir lime leaves, lime juice, etc. This paste can be used whenever you need to come up with a quick batch of tom yum soup and avoid the large pieces of ingredients you usually put into the stock.