One of the regulars in a Facebook worm composting group likes to use this guideline: If it was ever alive, the worms will eat it. And that is true, with a very few exceptions. After that, it is a matter of personal preference.
Feeding is as much an art as it is a science. As you gain more experience, you will get a feel for how much of what types of materials you can add to the bin. As the bin gets more established, food will be eaten faster. Some foods create a mucky mess. Others break down slowly. Others are eaten very quickly.
Many of the foods that are on people’s don’t feed list, are either there for our own convenience, or because of misunderstandings.
Worms will eat onions. But they can stink while they break down, and onion skins break down slowly. Other foods will also stink or break down slowly. But you have time. I have given my worms a whole head of cabbage, and it was eventually eaten. The same for rotting potatoes. The smell from the broccoli wasn’t so bad after a few days.
Citrus contains a chemical that is toxic to worms, but it breaks down in the bin, and worms will devour citrus once that chemical breaks down.
Dairy can stink as it breaks down and attract pests to the bin, but my worms have eaten whole milk, yogurt, sour cream, cottage cheese, whey and cheesecake with no problems. They would not touch cheese or butter.
Greasy foods are discouraged, but I have fed my worms shredded cardboard soaked in hamburger grease, and they ate it. I have fed them shredded cardboard soaked in olive oil, and they ate it. They have also eaten peanut butter. The key with greasy foods is to have enough bedding to totally absorb the grease.
Foods that are high in acid are discouraged, but my worms never got that memo. They love tomatoes almost as much as I do. They are high in moisture and simple sugars, both of which attract worms.
Pineapple and papaya are discouraged because they contain enzymes that act as meat tenderizers. But there are people who report feeding both to their worms with no problems.
Hot peppers are also discouraged, but people have run experiments with hot peppers, and the worms had no problems with them. In my own experiments with jalapeno peppers, the worms ate them just as quickly as any other food scraps.
My worms would not eat sugar, dog food, gelatin, butter or cheese. So there are some things that the worms won’t eat. I left some macaroni and cheese buried in the bin for several months. When I dug it out, the macaroni was gone, but the cheese had not been touched.
Grains in large amounts can go sour in the bin or create a mold bloom. I almost killed off a bin of worms by feeding too much rice. In small amounts, mixed with other foods, it was fine. A mold bloom caused by moldy grains will suck the moisture out of the surrounding bedding, creating a dry, hard mass. After the mold has run its course, worms will move in
Some people don’t like to bring organic matter in from outside because of the extra critters that can come in with it. I got pseudoscorpions in my bins when I brought leaves in to use as bedding.
Meat can be a problem. I have abandoned 2 meat experiments when they were overrun with maggots, but when I buried a fish fillet deep in the bin, it broke down just fine with no maggots and no complaints from the worms. There are people who have buried animal carcasses in their bins with no problems.
A lot depends on how you manage the questionable foods. Bury it deep and mix in a lot of bedding, and you should have no problems.
My advice is to follow the usual guidelines when you start out, but as the bin gets established, and you get used to the art of feeding your worms, don’t be afraid to break the rules. Start out small, and see how your worms respond.