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This question came up recently in a newsroom discussion over our recycling setup (a cardboard box with “aluminum cans” written on the side – I take it to my town recycling when full).

My understanding was that crushed cans can confuse the machinery used in single-stream systems (places where you put all recycling into the same bin). The machines “see” the shape of items when determining where to put paper, glass, ferrous metal, aluminum, plastic, etc., but crushed cans don’t look like cans so they can go in the wrong place, fouling the system.

On the other hand, as I understood it, if you’re in a place where you have to manually separate cans from paper, glass, etc. – like my town – then crushing cans to save space is fine. They get shipped straight to wherever aluminum goes to get recycled, regardless of shape.

I wasn’t entirely sure this was right, however, so I asked Jeff Weld, director of communications for Casella, which has the recycling contract for many New England towns and cities including Concord NH, where I am at the moment. He told me of a further complication.

Weld said that for Casella, crushed aluminum cans are no problem even when a collection is single-stream because “We use eddy currents to sort aluminum from ferrous metals, so it’s not a shape issue.”

Eddy currents are one of those things that make electromagnetism seem like magic. Aluminum isn’t attracted to magnets, obviously, but if you spin a magnet near aluminum or other material that conducts electricity, it creates a current within the material that can literally push it around. Eddy currents are used to send aluminum cans flying off a conveyer belt into their own bin, separate from the non-metallic stuff. Very cool.

So in conclusion: if you’re in a Casella-contracted community, crush your cans even if it’s single-stream. If you’re not sure who has the contract and if your town uses single stream collection, it’s probably best to leave your beer and soda cans in their natural state. If you manually separate your recycling, crushing is fine.

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