Plastics Recycling System

Here’s a handy chart detailing the various plastics used in packaging and products, identified by their recycling number. It’s handy to figure out what you can do to a given plastic bottle, in terms of heating or storing stuff in it.

I found this chart after a discussion on whether it was safe to microwave milk in yogurt containers, as part of the sterlization process for making yogurt at home.

The yogurt containers I have from the store are labeled with recycling code 5 (Polypropylene), which is the code found on, say, Tupperware. With a melting point of 145C, this should be safe for any reasonable microwaving application. (Though I suppose there are people who believe that microwaves and plastic don’t mix in general, as noted, polypropylene is used in your lunch box, so if reheating leftovers in the container is fine, so is sterilizing milk for yogurt).

This page has recommendations for cleaning plastic laboratory containers, and notes that autoclaving polypropylene is perfectly fine.

I’m not sure how yogurt companies make their yogurt. I’m pretty sure — given the smoothness and lack of whey — that yogurt is incubated in the containers themselves. How do yogurt makers sterilize their containers in the manufacturing process? Sterlize beforehand? Put hot, just-pasturized milk directly in the containers and cool down the whole thing on the line?

One Response to “Plastics Recycling System”

  1. Jill Says:

    Hi cjc – thx for this link – there’s been urban legend emails going around about heating/freezing in plastic – see
    (I’ve received this email a couple of times)
    Freezing looks like it’s totally fine – microwaving potentially releases harmful chemicals. Me, I’d rather heat in glass. – J