Which has a smaller footprint — canned or frozen vegetables?

Question

When fresh vegetables aren't an option, many sources indicate that frozen vegetables are generally better than canned (see here, here, and here, for example).

However, how do the environmental impacts compare? I can think of a few pros and cons for each:

• Canning is more energy-intensive process initially, due to the need for making and sealing the can
• Cans are heavy, and canned veggies are stored in water usually, adding shipping weight
• Cans can be recycled, where many types of frozen veggie packaging can't
• Freezing takes a lot of energy
• Frozen veggies must be shipped and stored in the freezer, meaning continuous energy consumption

There are likely other factors I am not thinking of as well. How do all of these stack up? Are canned veggies sufficiently better for the environment than frozen that I should just eat a few more to make up for the (minor) loss of nutrients?

Answer 1

So mostly your decision should be based on environmental impact of canned versus frozen since it appears the nutritional content is about the same. However from my reading of labels of canned foods, the sodium content can be much higher than plain frozen vegetables and added sugar may be a problem with some products such as yams.

See Fresh, Frozen and Canned Vegetables: Is There Really A Difference in Nutrient Levels?

According to a number of studies, fresh vegetables lose about half of their vitamins in just a matter of days after being harvested, if not properly chilled or sustained. And even after you refrigerate the veggies they still lose at least 50 percent of their nutritional value in about a week's time.

So unless you and your neighborhood rabbits are eating the stuff right out of the ground, you're going to lose quite a bit of the potential nutrition upfront.

The good news, according to Amy Jamieson-Petonic, a registered dietician and spokesperson for the Academy of Nutrition and Dietetics based in Cleveland, is that there is actually very little difference between fresh, canned or frozen vegetables, so consumers shouldn’t blindly plunk down extra money for fresh produce.

See also this article from Silgan Containers Canned Foods: Frequently Asked Questions which provides some information about canned foods as well as this page from the company about canned foods and sustainability.

I am not sure that there is much energy difference between canning and freezing vegetables. Both must be processed though several stages of preparation before either being canned or being frozen.

However once canned, canned vegetables require much less energy since they can just be stored. Frozen vegetables require continued energy use to maintain being frozen. The difference in energy is when being stored and when being transported.

As you pointed out cans may be recycled and I know that I do. Plastic will not.

This article comes to the conclusion that canned versus frozen so much as production impact are about even. Buying Frozen Veggies Versus Canned: Which is Greener?

All told, for 450g of corn, the can totals out to be 2,306 kcal, while freezing requires 2,272 kcal. Pretty much a dead heat...Except when you consider that you can store the can in the cupboard without any additional input of energy.

Food, Energy & Security assumes that it's going to take about 120 kcal/month of energy to store each package of frozen corn. That means that if that corn sits around in a freezer for more than about 100 days, the very slight advantage it has over canned corn is gone.

The verdict: In terms of energy usage in packaging and processing, freezing and canning come out pretty even.