“How many micronutrients are lost when canning and preserving? What about dehydrating?” —Rainbow Nutrition & Health
First things first: All you readers out there, raise your hands if you know what a micronutrient is.
Don’t be shy.
I thought so.
For the deets, you’ll want to take a look at Iowa State’s handy publication on key nutrients, but here’s the takeaway. Nutrients can be divided into two types: macro and micro. The key macronutrients are protein, carbohydrate, fat, and water. We need all of them in large quantities.
Micronutrients, which we need in small amounts, include vitamin A, thiamin (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), folic acid, vitamin B12, ascorbic acid (vitamin C), vitamin D, vitamin E, calcium, iron, magnesium, and potassium. Micronutrients are not the same thing as phytonutrients, which are more correctly called phytochemicals. Those are naturally occurring chemical compounds in plants that have protective, disease-preventing effects in humans.
Canning—whether in a boiling-water canner or pressure canner—preserves food by heat-processing it just long enough to destroy the microorganisms like molds, yeasts, and bacteria (including Clostridium botulinum, which causes botulism) that lead to spoilage. Canning also stops the naturally occurring enzyme reactions that also lead to decay in food. One obvious advantage to home canning is that you can “eat local” all winter long. Another is that you control the ingredients, thus avoiding the added sugar, salt, and preservatives present in most commercially canned foods.
In canning, however, the heat process can destroy up to half the vitamin A, vitamin C, and thiamin present in food. Other vitamins and phytochemicals are more stable. In fact, canning improves the nutritional value of some foods—for instance, the tomato, our primary source of lycopene, a phytochemical linked to the prevention of cancer and other diseases. Heat-processing actually boosts the body’s absorption of the compound.
Something to factor into the overall equation (nutrition is far from simple) is that most fruits and vegetables start to lose vitamins as soon as they are picked, and produce picked before it’s fully ripe (the better to withstand shipping) has less nutritional value than what is left to ripe on the plant. The journey of fresh produce from farm to supermarket, co-op, or health food store can take as up to two weeks.
That’s why, if at all possible, it pays to use your food dollars at a farmers market, where you are far more likely to find produce at its peak of ripeness and nutritional potency. Even when that produce is preserved, you’ll still be ahead of the game, health-wise. (And speaking of farmers markets, guess what? It’s National Farmers Market Week! Thanks to the American Farmland Trust, you can vote for your favorite right here.)
Long story short: If, in addition to preserved foods, you enjoy plenty of ultrafresh green and brightly colored vegetables, fruit, and other foods rich in micronutrients (click here for a more in-depth list) your body will get what it needs for optimum health.
Okay, a quick word about dried fruit: It can also be higher in nutrition than fresh because it has less water, which means that you get more solid fruit per ounce. Or not, depending on what vitamin or mineral you’re talking about. According to Dummies.com (gotta love it), a medium-size fresh plum contains 0.1 milligram iron and 670 IU Vitamin A, while the equivalent weight in dried plums (a.k.a. prunes) contains 2 milligrams iron and 952 IU Vitamin A. But a fresh plum is much higher in Vitamin C than a prune (dried plum). Go figure.
I am a terrible snob about dried fruit, thanks to David Karp, one of the world’s great authorities on fruit and former contributing editor at Gourmet. See his tips for finding the best dried fruit in the L.A. Times.
Or, if you are an energetic DIYer, dry your own. But here’s the deal: As with canning, for food-safety reasons, promise me you’ll use the right equipment for the job and follow procedures to the letter. Below are a few books that may be of interest; I know that sounds quaint, but honest-to-god physical books kind of suit the old-fashioned subject matter, don’t they? Plus, you will look back on the well-thumbed jam- and tomato-sauce-stained pages with great pride. So visit your local independent bookstore or order online.
- Ball Complete Book of Home Preserving, edited by Judi Kingry and Lauren Devine
- Putting Food By, by Ruth Hertzberg, Beatrice Vaughan, and Janet Greene
- Complete Book of Home Storage of Vegetables and Fruits, by Evelyn V. Loveday (includes directions on building several different types of home dryers)
One great online source is the Complete Guide to Home Canning, from the USDA National Center for Home Food Preservation. Download it for free (our tax dollars at work!) right here.
Lastly, don’t forget to check your local county extension office for advice and even hands-on workshops. Click here to see what Cornell’s cooperative extension office in Tompkins County, for instance, has to offer.
Have you ever tried canning? Did you find it was worth the effort?