When people think about canning, one question that is frequently brought up is nutrition. Many people are aware that the canning process decreases the nutrients found in the food. While it is true that canning reduces the levels of some nutrients, we often overstate the loss. Canned foods can still be very healthy.
The truth is, all foods begin to lose vitamins once they are picked. In many foods, half the vitamins may be lost within a few days unless the produce is cooled or preserved. Even in the refrigerator, produce may lose half its vitamins within a week or two. Even though the canning process does decrease vitamin levels, those vitamins may have been lost anyway before the foods were consumed. The real question in regards to nutrition is how fresh a food is when you buy it or if it was canned of frozen while it was still fresh.
In terms of actual vitamins lost, the heating process typically destroys one-third to one-half of vitamins A, C, and some B vitamins. The exact numbers really depend on the food being canned. However, once canned, the loss of these nutrients is minimal and estimated to be 5 to 20 percent per year. Other nutrients are not strongly affected by heat and will have only slightly lower amounts than fresh produce.
The real key to healthy canning is speed. You want to can produce when it is fresh. For most fruits and vegetables, the ideal time would be within 6 to 12 hours from picking. If you are unable to can them right away, you need to store them in a cool, dark place (like a cellar or refrigerator). However, for best quality, apricots, nectarines, peaches, pears, and plums should be ripened for one or two days before canning.
Another common health question involves sugar. People are often shocked when the see the high amounts of sugar or salt some recipes require. While we defiantly recommend cutting down your consumption of these products, they do have their purpose in canning. This means eliminating them is often easier said than done.
Through osmosis, sugar or salt replace some of the water present in a fruit or vegetable (thus, dehydrating the food). This process reduces oxidation and aids in the preservation of a food’s natural texture, shape, and color. Sugar or salt molecules in solution also decrease the water activity (sometimes notated: aw) in the food. Having less “active water” available inhibits the growth of potentially harmful microbes.
Artificial sweeteners are chemically quite different than sugar and do not act the same way as sugar does in water. So a strait substitution of sugar in a recipe is not likely to turn out well. However, many stores now sell low-methoxyl pectins which allow you to use less sugar than you would with a regular pectin. This works because low methoxyl pectins rely on calcium, rather than sugar, to get jams to set. If you search online, you will also find various low or no sugar canning recipes. Some recipes—and some foods—will work better than others.
While sugar is commonly added to foods that are naturally sweet, salt is more typically added to savory foods. In these recipes, salt performs the same functions as sugar, but the taste is more complementary. When you are choosing a recipe, salt and sugar content is something to keep an eye on. Choosing a healthy recipe is the most straightforward way to control you intake of these products.
You can reduce your intake of sugar and salt from canned products in a few ways. For fruits, you can discard the water or syrup in the can and eat only the fruit. (Of course, this will not work with jams.) For vegetable products canned with salt, most of the salt can be removed by rinsing the vegetable with clean water. If they taste too plain after this, you can always add a dash of fresh salt. The salt you add will be quite a bit less than there was before rinsing.
We hope this cleared up any questions you may have had regarding canning and nutrition. Canned foods can be very nutritious and can certainly be part of a healthy diet. Remember, it is the freshness of a food when it is consumed, canned, or frozen that has the largest impact on that food’s nutrient content. In our next article, we will be discussing another important topic: Canning and Safety.
References:”Canning Basics 1: Introduction.” University of Minnesota Extension. Ibid. ”Ensuring High Quality Canned Foods.” University of Minnesota Extension. “How Do Salt and Sugar Prevent Microbial Spoilage?” http://www.scientificamerican.com/article/how-do-salt-and-sugar-pre/.