Ask the Editor: Are Eggshells Really Compostable?

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Q: What’s the truth about eggshells? Can or can’t they go into the compost bin? – Heather Fulton

While eggshells are technically compostable, there are some important factors to keep in mind before tossing them into a backyard compost pile. Photo: Wikimedia Commons/Llez

A: Technically speaking, eggshells are compostable. But there’s a catch.

According to Frank Franciosi, composting department manager for Novozymes North America Inc., there is a potential health risk of tossing eggshells into a backyard composting system if they contain salmonella.

Most home composting systems do not exceed 130 degrees Fahrenheit, which is mostly due to a small mass in volume (less than a cubic yard).

“Salmonella and other detrimental pathogens cannot survive high temperature composting,” Franciosi says. “So it’s important for the homeowner to actively compost their eggshells in a hot compost pile.”

To generate more heat, Franciosi says a composter must keep in mind the mixing rule: one-third green items rich in nitrogen (food scraps, grass clippings), plus two-thirds brown materials with a high carbon content (dead leaves, hay and straw, paper products, coffee grounds). Also, keep wood chips a half inch to 1 inch in the pile for pore space, which will provide oxygen. Lastly, turn the pile frequently, at least once a week.

Franciosi also recommends purchasing a compost thermometer to check and chart the pile’s temperatures, indicating that high temperature organisms are actively composting.

Another important factor to be aware of is the moisture content. Franciosi recommends maintaining a pile moisture of 40-55 percent. What does that exactly look like? According to the NYC Compost Project, “Optimal moisture levels for composting occur when materials are about as moist as a wrung-out sponge – obviously moist to the touch, but yielding no liquid when squeezed.”

Knowing the general rules about home composting is important for any household looking to start a backyard system. But, if you have the extra cash on hand, there is an easier way to ensure scraps and organic waste is breaking down properly.

Purchasing an automatic compost bin is great for beginners or households looking to compost more than just vegetable peelings and dead leaves. For example, the NatureMill compost bin mixes automatically, restricts odor and makes compost in just two weeks.

The biggest bonus of an automatic composter is that it generates extremely high heat. This mean that, unlike most at-home composting systems, you can throw in meat, fish and dairy products. This type of bin will set you back about $200, but you can definitely toss in those eggshells without a second thought.

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Earth911.com’s Ask The Editor series tackles your toughest environmental and recycling dilemmas. If you have a question about reducing, reusing or recycling, e-mail the Editor, awills[at]earth911.com or send us a message via Facebook or Twitter.

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