There are a lot of factors that complicate what seems like a simple question.
Recently Tom Oder addressed the question Is freezing or canning better? He concludes that “it depends” — on variables like preference, time and the type of food. But there are other variables that perhaps are worth mentioning too.
Which has a smaller energy footprint?
Canning involves boiling the jars of food to sterilize and seal them, a one shot burst of energy. However freezing the food requires continuous long-term consumption of electricity to keep the food frozen. The longer you store the food, the more it costs. An academic study published in the Journal of Food Science in 1980 calculated the energy use for processing and storing 50 pounds of vegetables and determined that freezing for six months used about three times as much energy as canning; for a year, it used six times as much energy.
But it’s hard to extrapolate this to today; new fridges use a third of the electricity used by 1980 fridges while electricity costs 2.5 times as much as it did then. The numbers also vary significantly according to whether the fridge is full or not. Chest freezers are twice as efficient as uprights, so a lot can be done to minimize electricity use.
A more recent analysis, done for a book that promotes dehydration and with unverifiable sources, concludes that freezing uses 15 times as much electricity and costs four times as much per pound as canning, when you factor in the cost of the equipment.
Which has a smaller physical footprint?
Another source, The Natural Canning Resource Book, made a couple of relevant points beside energy use.
Canning is less energy-intensive than refrigeration and long-term freezing. Frozen food stored longer than four months uses more energy than canning. Moreover, canning requires only a one-time use of energy, rather than a non-interruptible supply. Canning makes modern life with a small or non-existent refrigerator possible.
There are two important points there. If you’re worried about resilience, about dealing with power outages and other disruptions, canned food is a lot better than frozen food. If you’re living in a small space or a tiny apartment, if you’re a renter rather than an owner, it’s a lot easier to store canned food than it is to store a freezer. And as I say all the time over on TreeHugger, Small fridges make good cities.
On the other side of the table, that same study in the Journal of Food Science found that people preferred the taste of frozen food over canned by a long shot. And whatever method you use, the end result is that you want people to eat it and like it. So it’s not so simple.