InSinkErator lists egg shells, rice and pasta as fine to grind in every disposal series, with cold water running. Moen and Waste King ban clam and oyster shells, not egg shells. Some institutions still say skip all three. Small amounts with plenty of cold water are the safe habit, and a pile of leftovers belongs in the trash.
What do the disposal makers say?
InSinkErator's food guide lists egg shells, rice and pasta in the recommended list for every series it makes: Badger, Power and Advanced. Its list for the Badger series, the entry line, includes egg shells, pasta and rice, next to bread, citrus rinds and potato peels. InSinkErator says "Do NOT pre-load the disposal," and gives one routine for all of it: turn on cold water, turn on the disposal, feed waste in gradually, listen and wait for the grinding to stop, let water run a few seconds, then turn off the disposal and the water. The page adds a tip. Mixing food waste of different densities, shapes and textures helps the disposal grind well.
Moen and Waste King give lists of what to keep out, and eggshells are not on them. Moen says not to put in large whole bones, clam or oyster shells, whole corn husks, glass, china, plastic, metal items, hot grease or other hot liquids. Waste King says its disposal "will handle all normal garbages" but will not grind items such as plastic, tin cans, bottle caps, glass, china, leather, cloth, rubber, string, clam and oyster shells, aluminum foil or feathers. Neither names the shell of a hen's egg, rice or pasta. The shells they do name are clam and oyster shells, which are much harder.
Why do some sources say to skip them?
Georgia Tech's campus support page tells residents not to put dry or cooked pasta, dry or cooked rice, egg shells, coffee grounds, bones or grease down a disposal, because the drain "will become clogged and require maintenance to repair it." The page does not explain how, so treat it as a cautious house rule for a big building with many users.
There is a practical way to reconcile the two views. The makers are talking about what the disposal can grind. A building manager is thinking about what a whole building's worth of pipe can carry away. Both are reasonable. What you do at home depends on how much you put down and how well your line drains. Our page on what not to put in a garbage disposal at the holidays takes the cautious side for big meals.
### Which of the three is the biggest risk?
That depends on the amount, not the food. A few crushed shells are a small job. A pot of leftover rice or a pan of pasta water with noodles in it is a large load of food that has to be carried through a trap and a branch line. The makers' rule about gradual feeding exists for that reason. That is why the gradual-feed habit matters most with cooked rice and pasta.
### Does the size of your disposal change the answer?
It can. Waste King's selection guide sorts its disposals by use level: light for 1/3 horsepower, medium for 1/2, medium to heavy for 3/4 and heavy for 1 horsepower. A small unit is rated for lighter work, so a big batch of scraps asks more of it. Our page on what size garbage disposal you need shows how the makers match horsepower to a household.
### What about potato peels, bread and other starchy scraps?
The same split shows up. InSinkErator lists potato peels and bread as fine for every series. Georgia Tech lists potato peels as a no. The advice for eggshells, rice and pasta covers them too: small amounts, cold water and gradual feeding, or the trash for anything more.
Whichever view you follow, one rule holds for both: nothing in this list is a reason to skip the cold water. The water carries the ground food out of the unit and through the trap, and that is what keeps starchy scraps from settling where they should not.
How do you put these in safely?
If you choose to use the disposal, keep to this routine.
- Follow the six steps. Cold water first, then the disposal, then the food. Keep the water running a few seconds after the grinding stops.
- Feed a little at a time. A spoonful of rice or a handful of noodles is very different from a whole pot.
- Mix them with other scraps. InSinkErator's tip about mixed textures applies. Grind a few peels or rinds along with them.
- Crush shells first. The EPA's composting guide lists crushed eggshells, and crushing also makes sense before a disposal. A few crushed shells is the most you should send.
- Skip the grease. Rice fried in oil or noodles tossed in butter carry fat with them. Every maker warns about grease, and Phoenix Water Services says to let cooking oil cool in the pan and scrape it into the trash.
- Run cold, not hot. InSinkErator says to avoid hot water when grinding food waste. Our page on whether to run hot or cold water explains the rule.
### How do you know if your drain can handle it?
Test it, in a low-risk way. Grind a small amount with cold water, then watch the sink. If the water drains quickly and the sink stays quiet, the line is coping. If the sink drains slowly, gurgles or backs up into the other side of a double sink within a day or two, stop putting starches and shells down and have the line looked at. A disposal that hums or stops is a separate problem, and our page on humming disposals covers it.
Where should leftover rice, pasta and shells go instead?
For bigger amounts, the trash or the compost pile is a better home.
Eggshells. The EPA lists crushed eggshells as a compost ingredient, in the nitrogen-rich group with fruit and vegetable scraps. Rinse and crush them before you add them to a pile.
Rice and pasta. Cooked food is different. The EPA's composting guide lists meat, dairy and fats among what to avoid in a backyard pile. It also lists cooked food there, with a note that small amounts are fine. Since plain rice and pasta are cooked food, a big pot of leftovers does not belong in a home pile. Put those in the trash.
Pasta water. Cooking water is thin, and the makers say hot water is fine to drain between grinding periods. But keep noodles and starchy bits in the strainer. Tip the strainer into the trash, then pour the water.
When should you call a plumber?
Call one if the kitchen drain slows after you grind starches, if water backs up on the other side of a double sink, or if the disposal hums and stops. Our page on why a garbage disposal drains slowly helps you tell a jam from a slow line. If a jam is the problem, what to do when something falls into a disposal covers how to free it safely. Do not pour a chemical drain cleaner into a sink with a disposal and hope for the best, since Moen lists caustic drain cleaners among the products to keep out of the unit. HQ is licensed and insured, offers 24/7 emergency service for backups, and gives free estimates and upfront pricing.
For the full clog-prevention routine, see how to keep a garbage disposal clear of clogs, and for upkeep, how to maintain a garbage disposal so it lasts.