Chum is the signature ingredient in all of Plankton's menu items. As one of several major factors that causes the Chum Bucket to fail, the taste is highly considered foul in contrast to Mr. Krabs' Krabby Patty.
Role in series
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 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 can eat anything. On the other hand, Mr. Krabs' tasted quite good. Plankton continues to use chum in most of his products, despite its foulness and overall toxicity (many have vomited after eating it). In later seasons, his chum was still inedible but another quality in his restaurant, such as the Chum Caverns or a popular slogan, would draw in customers.
The Chum Bucket contains a variety of products that are mostly made out of chum:
Whale Blubber (Which is ironic due to Plankton's fear of whales)
Sprinkle of Anchor Rust
According to the episode "Jailbreak!," there is an alternate way to create chum. All that is needed is a toilet and:
Cultural fungus growth medium (An old sock)
Subtropical vegetal matter (A banana peel)
Organic filler (A bucket of trash)
Live bacterial culture (A recently used napkin)
After adding all of those, Plankton closes the seat and flushes it causing them to mix together and create the chum.
In real life, chum is inedible for people, which means it is not suitable for eating.
According to "The Krabby Kronicle," his chum was actually chum made from real live fish, which serve as the series' characters. Chum should already be meat from fish, as that is how it is in real life.
In the later seasons, some characters have gained the habit of eating chum despite tasting horrible to the customers that have already eaten it.
Most of the time, the chum bears a reddish-brownish color similar to that of real live beef patties.
Chummy Patties is the only food that Plankton serves that isn't actually made of chum. It is basically a pure grease sandwich.
According to the episode "Friend or Foe," chum is actually an ingredient in the Krabby Patty Secret Formula.
As revealed in "Jailbreak!," chum can actually be used to help pull off crimes.
Out of all the chum-related food, the Chummy Patties and Chum Fricassee are the only ones that Plankton has sold that actually tasted good.
In "Free Samples," it is revealed that Patrick Star is the only one who can eat chum compare to anyone else who eats it. Also, in "Chum Caverns," Patrick ate a lot of Plankton's Chum which means he is the only one who loves eating chum, though he doesn't know his chum is located in the Chum Bucket.
Despite the fact that the ingredients for chum (as explained by Plankton in the episode "Spongicus"), are only chum, many other things have been seen in chum such as an eyeball as seen in the episode "Drive Thru."
In real life, people use chum for bait when they catch fish.