What are the distinguishing differences of this soup in the countries where it is traditionally prepared?
@dymnyno, I think just about every Asian country has it's own 'hot & sour soup'. In SE Asia (like Thailand & Vietnam), the sourness comes from tamarind or limes and sometimes pineapple; the hot comes from fresh chilis. Add-ins are shrimp, beef, seafood, tomatoes, beansprouts, and/or tofu. Seasoned with fish sauce and herbs like
the Vietnamese ngò ôm (Limnophila aromatica).
The ones in China utilizes vinegar for the sour and white pepper or dried red chilis for the heat. Add-ins are minced meat and/or tofu, fungi (eg. mushrooms and woodears), bamboo shoots, and egg whites.