Chum is the signature ingredient in all of Plankton's menu items. In real life, chum is bait used by fishermen, made out of chopped fish.
Chum is incredibly unappealing to the fish population of Bikini Bottom, which prevents the Chum Bucket from having customers. Organs and eyeballs have been seen in Plankton's chum, but it is unknown where he gets them. Although mentioned in previous episodes, chum first appears in the episode "Friend or Foe."
Most of the time, the chum bears a reddish-brownish color. According to "My Two Krabses," chum contains the organs of living beings, giving it its color.
During Plankton's childhood, he and his former best friend, Mr. Krabs, saw how their classmates' favorite burger joint gained "li-spect" and wealth.
Pursuing their own yet combined goals, they attempted to open their own restaurant with their own recipe and burger, which turns out to take no attention. Their burger poisoned Old Man Jenkins, resulting in an argument that sparked their hostile relationship.
Mr. Krabs made his own burger, the Krabby Patty, and Plankton used chum for his burger. Plankton's creation proved foul even to those who could eat anything. On the other hand, Mr. Krabs' tasted quite good.
Role in series
Plankton continues to use chum in most of his products, despite its foulness and overall toxicity, as shown by many having vomited after eating it. In later seasons, his chum is still inedible but another quality in his restaurant, such as the Chum Caverns or a popular slogan, such as "Chum is Fum" will draw in customers.
"Friend or Foe"
Chum was originally in the burger recipe that Mr. Krabs and Plankton made as kids. However, the burger poisoned Old Man Jenkins when he ate it, causing Krabs and Plankton to accuse each other of tainting the burger. The two soon become foes and try to create their own burgers to outdo one another, with Plankton using chum in his burgers.
Chum Patties appear in the scene with the giant abyss monster. The chum came from Chum Changes, which Plankton used to destroy the submarine. It punches holes through the wall and chum starts to go into the submarine. One of them lands on a bun. The monster, while still in anger for more food, takes a look inside for food. He then sees this food and asks about if he can try it. SpongeBob and Patrick then give it to him.
The monster likes it and he asks for more. They start to make more until the sea monster is stuffed.
Plankton offers a chumstick to Incidental 104, who later considers going to the Krusty Krab for a Krabby Patty instead after discovering that chumsticks cost 10 dollars. Plankton negotiates with her and Debbie stubbornly agrees to purchase his food.
After taking a bite of the chumstick, she spits it out immediately upon its foul taste.
After Plankton complains about the fact that he has no customers, Nat comes to the Chum Bucket and orders a chumstick. He then goes back the next day and the day after that, becoming Plankton's only regular customer, and the only person who actually likes his chum. However, in the end, it is revealed that he only ordered chumsticks because Karen paid him, and he actually hates the food, so much that he already had to go to the doctor twice.
Plankton exits the Chum Bucket kitchen with "the chumstick that's finally gonna drive Krabs out of business." Andy Yellowtail, the health inspector, quickly shuts down the Chum Bucket due to one of SpongeBob's lies that Plankton uses fish in his chum.
After Patrick changes the Chum Bucket slogan, this brings Plankton new customers who actually eat his food in spite of its horrible taste, which makes Mr. Krabs jealous as the Krusty Krab loses business in favor. Plankton feeds a chumstick to SpongeBob, which causes the disguise he and Mr. Krabs were hiding in to explode. SpongeBob is seen wiping his tongue with a kitchen sponge afterwards, obviously disliking the taste.
After Plankton moves the Chum Bucket underground into the eponymous location, he gets a lot more customers due to his fancy atmosphere. The customers agree to actually eat his food without regard to the horrible taste.
SpongeBob learns that the cure to the Secret Patty's side-effects is actually chum. He then uses it to return everyone back to normal after they mutated into Krabby Patty zombie monsters, which helps him save the day.
Plankton's chum gets rotten during this episode, and he has to find a way to hide his chum. After hiding all of it with the help of SpongeBob through tricking him, he ends up succeeding at his goal. However, when SpongeBob tries to push down the last piece of rotten chum into a sewer, he ends up spreading all the rotten chum all over town and causes it to rain down slowly like snowflakes. This results in SpongeBob realizing it is Chum Day and make the citizens realize that too, with Bikini Bottom's kids already having the spirit of Chum Day.
Despite all the happiness, a health inspector enforces the law against Plankton for chum dumping and spreading chum all over. Plankton cannot pay the fine, so the inspector gives him another option: to eat all the chum. Plankton does this over a long period of time and becomes extremely big in the process.
This episode reveals Mr. Krabs' love for chum as back when he was in the navy, he tasted chum and fell in love with it. Plankton finds out about this when Mr. Krabs is searching through a trash can and the latter admits his love for chum. Plankton tricks Mr. Krabs into giving the formula by offering him a life-time supply of chum, which ends up being a hoax. Mr. Krabs tries to get the formula back but drops it into the chum, making Plankton swim in the chum to find the formula and Mr. Krabs eats all the chum so he could get to the formula quicker.
Mr. Krabs loses his appetite for chum from eating the entire supply of it and also ends up eating Plankton and receiving the formula in the process too.
The Chum Bucket contains a variety of products that are mostly made out of chum:
As revealed in "Jailbreak!," chum can actually be used to help pull off crimes and as a result, the criminal community holds Plankton in high regards.
In "Free Samples," it is revealed that Patrick is the only one who can eat chum compared to anyone else who eats it. Also, in "Chum Caverns," Patrick eats a lot of Plankton's chum, though he does not know the food item is sold at the Chum Bucket. In "The Inmates of Summer," Patrick and SpongeBob eat chum while inside the confined space of the Inferno Island prison.
Despite the fact that the ingredients for chum are only just that, chum, many other things have been seen in it, such as an eyeball, as seen in the episode "Drive Thru."