A public service announcement from my mom the food scientist: How to preserve foods so they won’t kill you later.Posted: June 26, 2011
“Do you like the taste of C. botulinum spores? I didn’t think so! Read this article – it could save your life!”- Run Run Rhubarb
Acidity of foods helps determine the type of heat processing or home canning required for safe preservation. The term “pH” is an index of acidity. The lower its value, the more acid in the food. Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes.
There are two safe ways of processing food:
- The boiling water bath method is safe for acid foods that have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters. In this method, jars of food are heated completely covered with boiling water (212°F at sea level) and cooked for a specified amount of time (consult your Blue Book). Processing acid foods at boiling water temperatures will destroy yeast and molds, the most common forms of spoilage microorganisms in these foods. Heat-sensitive bacteria are also killed. Those that are heat resistant, such as C. botulinum spores, are prevented from multiplying because of the high acid conditions of the food. Although tomatoes usually are considered an acid food, some varieties are now known to have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products with unknown pH must be acidified to a pH of below 4.6 with lemon juice, citric acid, or vinegar. Properly acidified tomatoes are acid foods and can be safely processed in a boiling-water bath.
- Pressure canning is the only safe method of preserving vegetables and other low acid foods such as (shudder) meats, poultry and seafood. Jars of food are placed in 2 to 3 inches of water in a special pressure cooker which is heated to a temperature of at least 240° F. This temperature can only be reached using the pressure method. The spores of C. botulinum grow well in low acid foods, in the absence of air, such as in canned low acid foods like meats and vegetables. When the spores begin to grow, they produce the deadly botulinum toxins. Botulism spores are very heat resistant. They may be destroyed at boiling water temperatures, but extremely long times are required. By the time you water bath-processed jars of green beans sufficiently to destroy these spores, you’d have a gray-green mush of nutrient-free fibers. You might as well eat grass clippings.
Don’t even consider any other so-called “traditional” methods you may have heard of: “Open Kettle” method or the “Oven Canning” method (don’t even ask!). How about processing filled canning jars in the dishwasher? Adding aspirin to your jars? No, no, no, and no!
My mom loves rhubarb as much, if not more than I do. I asked her to use her food science expertise to write about the wonders of rhubarb.
Fruits, perching precariously on the second tier of the food pyramid (hovering with vegetables above the cereal and grain group), are enjoying improved status on the new food plate nutritional model. We say it’s high time. Fruits have always been our favorite food group, contributing that valuable juicy/crunchy, sweet/tart, pleasant smelling, attractive looking component to our diet. The distinction between a fruit and a vegetable can often be a fine one. Tomatoes, cucumbers, and squash are botanically fruits, but are looked upon as vegetables. Rhubarb, actually a stem, is considered a fruit.
And in spring, when our thoughts turn to pie, we traditionally think of this “pie plant” stem, steaming through a lattice crust, juices flowing freely over the side and onto the oven floor, smoke alarm blaring, dog howling….it’s all worth it. Alone or in combination with fresh strawberries, peaches, blueberries, raspberries, or any other sweet fruit, rhubarb in pie is a classic!
The nutritional make-up of rhubarb is actually very interesting. Containing only 16 calories per 100-gram (3/4 to 1 cup) raw, cubed pieces, rhubarb is a pretty decent source of vitamin A, potassium, and calcium. As its tart taste implies, rhubarb has a high acid content – malic and oxalic acids mostly. The oxalic acid has the distinction of cancelling out much of the calcium contribution of rhubarb, as it combines to form a less soluble salt, calcium oxalate. Although the tartness of rhubarb is part of its charm, most normal people add too much sugar, making it tastier and higher in calories. The addition of other sweet fruits and berries, as mentioned before, allows us to add a bit less sugar. Some individuals have been observed crunching away on a stalk of raw rhubarb with only a sprinkling of salt to cut the tartness! In fact, scientists have studied this interaction of salt with acids and have additionally observed that small concentrations of salt also increase the apparent sweetness of sucrose. This explains why some people sprinkle salt on grapefruit and why a small amount of salt improves the flavor of fruit pies.
Final note of caution: Only the stems of the rhubarb plant are edible! The leaves and roots (should you be so inclined) are toxic with high concentrations of oxalates. Remove the leaves immediately upon harvesting and supervise your children and pets!