If you're concerned about your environmental footprint, switching from single-use bags and wraps to reusable food storage containers from Rubbermaid, Tupperware and other manufacturers can reduce the amount of waste you generate. If you use them intelligently, you can also cut down on the amount of food you waste. You will need to exercise a slight degree of caution if you want to microwave in them.
Concerns About Microwaving in Plastic
Part of the appeal of managing your leftovers with plastic storage containers is that they can take your food to the fridge or the freezer and then into the microwave when you want to reheat and eat it. For some consumers, though, the idea of microwaving food in plastic is a concern. There is some basis for that: Not all forms of plastic are intended for use in the microwave, and might not perform well.
Another potential issue is the presence of a hardening agent called bisphenol A, or BPA, in the plastic. It can leach into foods if they happen to be in contact with that plastic while it's heated. There's no clear evidence of harm from the levels of BPA that are permitted in food-safe containers, but it's something the medical, scientific and regulatory communities monitor closely.
In the case of Rubbermaid containers, because of these persistent concerns about BPA, the company phased out that additive back in 2009. All of its current food storage containers are BPA-free, so unless you've recently acquired a stash of decades-old containers from an older relative, you should be able to use what's in your cupboard without fear.
Most lines of Rubbermaid food containers are intended to go from fridge to microwave. The popular line of lightweight, inexpensive Rubbermaid TakeAlongs is microwave safe, for example. If you want to know for sure whether a given product is microwave-safe, check the underside for the words "microwave-safe" or a microwave logo. Either one indicates that your container is safe to use in a microwave oven.
Don't Microwave Too Hot
Knowing that your container itself is microwave safe is only the starting point. For you and your food to remain completely safe, you'll also have to use the containers correctly.
The biggest single thing to remember about microwave use is that high heat is not your friend. Rubbermaid containers are designed to be safe at temperatures of up to 212 degrees Fahrenheit, which is the boiling temperature of water. Beyond that they can melt or become deformed.
A mostly watery food, like soup, will never rise above that temperature. Neither will things like leftover vegetables or meatloaf. Fats and sugar, unfortunately, can get much, much hotter in the microwave. You should avoid reheating really fatty foods, or sugar-based syrups and sauces, except in short bursts and under the closest of supervision. Never use your plastic containers to crisp bacon, for example.
Sometimes You Need to Vent
There are times in life when you just need to vent, and one of those times is when you're reheating food in the microwave. Rubbermaid containers have tight-fitting lids to keep food fresh, and if you reheat them with the lid snapped firmly in place, you're asking for trouble.
As the food inside heats up, pressure can build up inside the container. This poses a lot of potential problems. One is that the lid may blow off and spatter food across the inside of your microwave. Pressure can also raise the temperature inside the container past the boiling point – that's how pressure cookers work – and it can damage your container. There's also a risk of hurting yourself when you pop the lid on the container and all that superheated steam comes rushing out.
The trick is to open at least one corner of the lid to create a place where hot steam can escape. Some Rubbermaid containers, notably the Microwave'n Savers, have a vent built into the lid that will release pressure automatically when heated. If the lid to your product doesn't have a visible pressure release vent, it's safest to assume that you should vent it manually.