There's nothing quite as satisfying as a fresh pizza on a Friday night.

When it comes to recycling greasy pizza boxes, however, the results can be less than ideal. To understand why, let's take a look at how paper and cardboard recycling works.

Paper recycling process

The heat processes required for glass, metal, or plastic recycling can burn off small amounts of food residue. Unless there is an excessive amount of food left on recyclables, your glass, metal, and plastic materials will come out just fine.

But paper recycling is another story. Since paper doesn't get heated during the process, grease and oil combine with the pulp, which can ruin the entire batch.

Once your paper and cardboard are sorted into grades and types, they move on to the paper mill where they may spend weeks in storage, ample time for food particles to turn rancid and attract insects or animals.

After that, they are washed with soapy water and sometimes chemicals to remove inks, plastic film, staples, and glue. The batch is then sent to a large receptacle where it's mixed with water to create a slurry.

That's where your greasy pizza box (or any paper product that's greasy) gunks up the works. Even though it's been through a soapy bath, if you've ever washed something full of grease or oil, you know that it takes quite a bit of effort and soap to remove it completely.

Once in the slurry, the remaining oil floats to the top and becomes impossible to separate. Depending on what type of paper the mill was going to make and how much contamination is present, the entire batch may be ruined.

To avoid contaminating clean materials, it is good practice to cut off the clean tops of your pizza boxes to send to recycling but dispose of the greasy bottoms in the trash.

Wish-cycling

Many of us have the best of intentions when we go to toss non-recyclables into curbside bins. Because we want an item to be recyclable, we 'sneak' it in, even when we know we're not supposed to. Enter, wish-cycling.

When this happens, unwanted items often cause problems. They may be caught early in the process, pulled out, and thrown in the trash, or they may make it through and contaminate an entire batch of clean materials.

Due to this troublesome issue, it's always best to look up your local rules when it comes to greasy and soiled products.

New advances in technology

In the simplest form of advanced technology, many pizza places have started to add an extra layer of corrugated cardboard under the pizzas to avoid the entire box becoming soiled. This layer of cardboard can then be disposed of, leaving the rest of the box clean and ready for recycling!

As for recycling facilities, there are some programs that are now accepting soiled paper products because of the machinery they have or the volume of paper collected that makes it feasible to accept these greasy items. These locations are few and far between, so make sure to check your municipal recycling requirements before you accidentally wish-cycle.

There are also some municipalities that accept greasy pizza boxes in their organic waste collection if they use an anaerobic digestion process to recycle organic waste. Check your organic program to see if this applies.

The bottom line

Grease and oil are two of the worst contaminants in paper recycling, and greasy pizza boxes are one of the biggest culprits. Check with your local recycling program to find out what you should do the next time you grab that final slice, but when in doubt, cut off the greasy parts, throw them in the trash, and recycle the rest.