While the soup is not actually seen, it is known that it is very hot, with steam coming out of it.
Role in episodes
"There's a Sponge in My Soup"
The Krabby Soup is the main focus of the episode. When Mr. Krabs tells the hippies they cannot be on Krusty Krab property to warm up, the hippies go inside the Krusty Krab kitchen and find a soup vat. Due to it still cooking, it is quite warm, so they decide to live in the soup. The hippies hide inside the soup for most of the episode, occasionally leaving when Mr. Krabs draws them out.
At the end of the episode, Mr. Krabs manages to move them over to Squidward's bathtub.
The Rich fish sees string in his soup, and complains. Mr. Krabs claims that it is for flavor and attempts to charge him $100 million for it. The rich fish is about to give him money when SpongeBob takes away the string, and keeps it to himself.
When Mr. Krabs gets angry, the soup is seen steaming on his back. SpongeBob grabs it from his back and sniffs it.