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.

Answer 2

FYI, even if "fresh" is an option, it may not be healthier, nor better for the environment. E.g., some notes (from https://www.motherjones.com/environment/2013/09/benefit-of-frozen-foods/) about frozen foods:

1. Can be nutritionally equivalent, or even superior, to fresh. Some of the vitamins and minerals in produce start to degrade soon after harvesting…. Fruits and vegetables are frozen within hours of harvest, so that actually allows you to retain those nutrients.
2. May contain less pesticide. Before fruits and vegetables are processed, some of them are washed and put through a machine that jostles them around to remove remaining dirt and debris. Some are also blanched and peeled. Thanks to this prep work … processed fruits and vegetables generally have less pesticide residue than fresh conventional produce.
3. Can be better for the environment. “Fresh fruits and vegetables require cold storage, too,” notes Sean Cash, an associate professor of agriculture at Tufts University’s Friedman School of Nutrition Science and Policy who has studied the environmental footprint of produce. “The difference between 28 degrees and 48 degrees is actually not that great.” Canned foods require even less energy, since they are shipped and stored at room temperature. What’s more, Cash says, while fresh specialty crops like berries are flown from South America, their frozen and canned counterparts generally travel by ship, on a fraction of the fuel. Even locavores, he adds, still have to get themselves to the farm or farmers market to pick up their veggies.
4. May result in less food waste. Home cooks often trash tough broccoli stems, fruit rinds, and vegetable peelings. But large-scale processors don’t always send that stuff to the landfill. Green Giant’s trimmings, for instance, are used as compost for its research farm, or given to local farmers as animal feed. Earthbound Farm, a large organic producer, sells some of its scraps to juice makers; its frozen spinach and broccoli waste goes to a manufacturer of organic dog food.

Also (from "Environmental impacts of vegetables consumption in the UK," https://www.sciencedirect.com/science/article/pii/S0048969719319758):

The impacts of air-freighted fresh vegetables are around five times higher than of those produced domestically. Even processed products have lower impacts than fresh air-freighted produce.

Back to the original question about canned vs frozen:

1. Another answer refers to a Treehugger article (https://www.treehugger.com/buying-frozen-veggies-versus-canned-which-is-greener-4854641) that refers to a book ("Food, Energy and Society," https://www.amazon.com/Energy-Society-Resource-Environmental-Sciences-dp-0713127619/dp/0713127619/). That book was written in 1979.
   • It's possible some methods have gotten relatively more efficient (e.g., freezers).
2. That said, going from what the book says, I'd pick canning. First, the math from the Treehugger article is suspect. 2,306 - 2,272 = 34 (kcal). If it takes 120 kcal/month to store a package of frozen corn, then only one week would be enough to make canned better. It was probably sitting a week in your supermarket already.
   • Also, canned is just simpler. You don't have to worry about having space in your freezer or power going out. (You could even not own a freezer.) You don't have to worry about reheating it. Canned lasts longer. It's more portable (e.g., camping, day trip). It stacks better.
   • It also encourages our civilization to use less energy for constant cold storage (e.g., supermarket freezers, plus the freezers they may have in the back, plus the freezer trucks, and the freezer warehouses).
   • When I check out the canned aisle, I see a lot more options for BPA-free liners, "no salt added," "no sugar added," etc.

Anyway, thanks for asking! I was wondering the same thing!