B1159 University of Wisconsin-Extension Cooperative Extension Wisconsin Safe Food Preservation Series Canning Vegetables Safely Barbara H. Ingham ate autumn finds Low-acid foods that would support some pantry the growth of C. botulinum include L shelves stocked meats, milk, eggs, and vegetables with row upon row of such as peas, carrots, corn and home-canned vegeta- potatoes. These low-acid foods bles. High quality home-canned veg- must be processed in a pressure etables can add nutrients and enjoy- canner to destroy any C. botulinum ment to family meals all year long. spores that might be present. For safe food unlikely to spoil, follow Foods with sufficient acid — fruits the directions in this publication for such as apples, peaches and pears — canning vegetables. will not support the growth of C. bot- Acids naturally found in foods can ulinum spores and can be safely help limit or control the growth of processed in a boiling water canner. many disease-causing microorgan- The acidity measure of a food that isms. However, most vegetables divides low acid (pressure canning) contain relatively low amounts of from high acid (boiling water acid.You can only prevent spoilage canning) is a pH of 4.6 (see the pH and possible foodborne illness by chart in the box on page 2). processing canned vegetables at temperatures to destroy harmful bacteria. Over the years, botulism from improperly home-canned foods has received a good deal of public atten- tion. Botulism is a potentially fatal poisoning resulting from consuming food that contains toxins produced by Clostridium botulinum, bacteria widely distributed in soils around the world. In the absence of air and in low-acid foods, the heat-resistant spores of this organism can grow and produce lethal toxins in food. This can happen without any sign of spoilage in the sealed jar. Even a taste of food containing this toxin can be fatal. CANNING VEGETABLES SAFELY 1 To destroy C. botulinum spores, low- A pH number Processing times must be acid foods must be processed at Select high quality measures acidity temperatures higher than the boiling long enough to: I allow heat to penetrate to the vegetables and alkalinity on a point of water (212° F at sea level). For high quality canned products, center of food or the coldest spot scale from 1 to 14. This can only be achieved by sur- use fresh vegetables at the peak of in the jar, and A pH of 7 is neutral. As the pH drops rounding the jars of food with pure eating quality. Ideally, vegetables I below neutral (pH < 7), a food becomes steam under pressure, using a steam reach temperatures needed to commonly grown in home gardens pressure canner. Under pressure, destroy harmful bacteria and bac- increasingly more acidic. As the pH should be canned the same day they water boils at a higher temperature. terial spores. are harvested. If this is not possible, increases from 7 (pH > 7), a food Use pressure canners to process refrigerate the vegetables until you becomes increasingly more basic or low-acid vegetables. Do not use How quickly heat are ready to can them. Refrigeration alkaline. In general, the foods we eat boiling water canners for low-acid penetrates depends on the: will slow the rate of quality loss. have a pH below 7.Very few foods are foods. I size of the jar, and Green beans, peas, sweet corn and alkaline; egg whites are the notable green leafy vegetables can lose A pressure canner is not the same I contents of the jar: exception (pH = 8). as a pressure cooker. Pressure quality very rapidly. Carrots, beets, – ratio of solid to liquid, and Here are some common foods and cookers or pressure saucepans are potatoes or winter squash can be used to rapidly cook meats, vegeta- – kind and size of food pieces. stored for a relatively long time their pH values. bles and other foods for a family Processing methods in this publica- without much quality change. For boiling water canning: meal. But they may not maintain tion take these factors into account pH 3.0 to 4.0—apples, berries, cherries, adequate pressure, and they heat and must be followed precisely to lemons, oranges, peaches, pears; and cool too quickly to ensure safe ensure safe home-canned food. Use pickles food. Do not use pressure cookers or only the jar sizes and packing styles For a list of recom- For boiling water canning or pressure saucepans for home listed for each vegetable. Process for mended vegeta- canning. pressure canning: the full time listed for each veg- bles to plant, etable. Follow directions in the pH 4.0 to 5.0—tomatoes with Pressure canners may have dial request the publi- gauges or weighted gauges. Pressure Vegetable Canning Guide beginning added acid * cation Vegetable Cultivars and Planting is measured in pounds per square on page 15. For pressure canning: inch (psi).When pressure is applied, Guide for Wisconsin Gardens A1653. pH 5.0 to 6.0—carrots, beans, onions, water boils at a high temperature. Other helpful information can be peppers, potatoes, squash; most Food can be processed in a pressure found in Disease-Resistant Vegetables meats canner quickly and safely at these for the Home Garden A3110 and pH 6.0 to 7.0—corn, mushrooms, high temperatures. For home Harvesting Vegetables from the Home canning, use pressure canners that peas; chicken Garden A2727.These are available maintain pressures up to 15 psi. from your county UW-Extension office or the address on the back page. * Tested recipes for canning tomatoes can be found in Tomatoes Tart and Tasty B2605, available from your county UW-Extension office or Cooperative Extension Publications at the address on the back page. 2 Wisconsin Safe Food Preservation Series CANNING VEGETABLES SAFELY 3 Canning vegetables uniform size pieces. Specific sugges- Do not add butter or fat to home- Filling jars tions are stated in the Vegetable canned products unless specifically Use standard canning jars free of Preparing vegetables Canning Guide beginning on page 15. allowed in a recipe tested for safety. cracks or chips. Do not reuse com- Adding butter or other fats to home- Wash all vegetables thoroughly mercial mayonnaise jars for process- canned food may slow the rate of under running water or through Optional ingredients ing in pressure canners, since the risk heat transfer, and result in an unsafe several changes of water. Lift the veg- Pickling or canning salt can be of breakage is great.Wash and rinse product. etables out of the water to drain so added to canned vegetables to the jars.You do not need to sterilize that dirt washed off will not settle enhance flavor. However, you can Do not thicken, add rice, barley or jars before filling when pressure back on the food.Trim or peel as omit or use less salt without risking pasta to canned vegetables. These canning. needed, depending on the veg- spoilage in low-acid vegetables. starchy ingredients absorb liquid Do not use jars larger than 1 quart etable. Spices or herbs may be added in during processing, and slow the way because safe process times are not the vegetables heat. Under-process- To limit nutrient loss: If directions small amounts before processing. available for larger jars. For some ing and unsafe food could result. call for cutting up vegetables for Heat treatments in this publication vegetables, even quart jars are not canning, do so just before you are are sufficient to render these addi- recommended for the same reason. ready to pack them into jars. Cut into tions safe. For high quality Check the Vegetable Canning Guide for recommended jar sizes for each canned products, product. If you use 11⁄2 pint jars, use use fresh vegeta- the process time for quarts. The yield of canned product from different vegetables varies greatly.The chart bles at the peak of below will help you estimate the amount of canned food you can get from each Vegetables may be packed raw or eating quality. Ideally, vegetables vegetable.Weights per bushel or crate are approximate. preheated and packed hot, as indi- commonly grown in home gardens cated in the guide. A few vegetables Yields for canned vegetables should be canned the same day they should be hot packed only. Pounds for Weight & About how are harvested. If this is not possible, Hot packing usually produces a higher Vegetable 1 quart jar measure many quarts refrigerate the vegetables until you are quality canned product and improves Asparagus 3 30 lbs./crate 10 to 15 ready to can.You may add small shelf life because it helps remove Beans, green, wax or Italian 2 30 lbs./bushel 15 to 20 amounts of salt, spices and herbs to trapped air from the food tissues, shrinks food, reduces floating, and Beans, lima (in pods) 4 to 5 30 lbs./bushel 5 to 8 canned vegetables. But do not add 1 increases vacuum in the sealed jars. Beans or peas, dry 3 ⁄4 25 lbs./bushel 6 to 7 butter or fat, or thicken these items Follow instructions for loose- or Beets (without tops) 21⁄2 to 3 52 lbs./bushel 17 to 20 with rice, pasta or starch. tight-pack filling. Some vegetables Carrots (without tops) 21⁄2 to 3 50 lbs./bushel 16 to 20 expand during processing, or will not Corn, sweet (in husks) 4 to 5 35 lbs./bushel 8 to 9 as kernels heat evenly if packed too tightly. Peas, green (in pods) 4 to 5 30 lbs./bushel 6 to 8 Potatoes, white 3 60 lbs./bushel 15 to 20 Spinach or other greens 4 20 lbs./bushel 5 to 8 Squash, winter or pumpkin 2 40 lbs./bushel 16 to 20 4 Wisconsin Safe Food Preservation Series CANNING VEGETABLES SAFELY 5 Use enough liquid — boiling water Follow these steps for successful or cooking liquid — to cover raw- Processing in a Pressure is measured home canning of vegetables: and hot-packed food.