Canning at High Altitudes
B is for botulism, C is for canning safelyThere. We said it. Botulism. The word that scares so many people away from home canning. According to the USDA, botulism is "an illness caused by eating toxin produced by growth of Clostridium botulinum bacteria in moist, low-acid food." What is the purpose of careful canning? To destroy such microorganisms in the food and allow you to store and eat it safely. Some foods are naturally high in acid and will be safe when properly canned in a hot water bath (pickles, berries, peaches, salsa, and chutney for instance) as shown above. High sugar levels in jams and jellies also retard the growth of microorganisms to some extent. Did you think tomatoes were high acid? They might be, or they might NOT. With the taste for sweeter tomatoes on the rise, the USDA now recommends checking the acidity of tomatoes and figs before choosing a canning method. This is an example of why it's important to stay up to date with the latest on canning guidelines. Here's the scoop: Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Figs also have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products must be acidified to a pH of 4.6 or lower with lemon juice or citric acid. Properly acidified tomatoes and figs are acid foods and can be safely processed in a boiling-water canner. Check pH with litmus paper, then if needed add citric acid or lemon juice and check again. Low-acid foods need the extra processing of a pressure canner to keep the bacteria at bay. Note the screws and clamps in the pot and lid of the pressure canner in the photo here. Low acid foods include most vegetables such as asparagus, beans, carrots, corn, peas, and pumpkin. The USDA has an overall guide to canning that clearly outlines which foods need which canning method. Follow the directions to the letter, from cleaning your kitchen, to sterilizing your jars, using correct canning methods and times, cooling your jars, and checking your seals -- and you should be botulism free. If you do suspect any botulism in a jar from your own pantry, or from a friend, use caution when dealing with the spoiled food. The USDA has a sobering reminder, Contact with botulinum toxin can be fatal whether it is ingested or enters through the skin. Remember the maxim: When in doubt, throw it out and throw it out with care, wearing a pair of rubber gloves.
High altitude canning timesCheck your altitude with your local County Extension volunteers such as Master Food Preservers or Master Gardeners. If you have these services in your county they will be listed in the front of your telephone book in the county government section.
Altitude changes for hot water bath canningCanning recipes assume you live at sea level. When you can above 1,000 feet you need to add more minutes to the processing time in a hot water bath. The extra time is needed because water boils at lower temperatures as the elevation increases, so you need to boil longer to kill the microorganisms. The USDA chart above shows how much the boiling temperatures drop with altitude. According to Colorado State University, you should adjust your hot water bath canning times: If the sea level time is less than 20 minutes, increase the processing time by 1 minute per 1,000 feet above sea level If the sea level time is more than 20 minutes, increase by 2 minutes per 1,000 feet
Altitude changes for pressure canningHot water bath canning is based on the minutes in the boiling water. Pressure canning is based on pounds of pressure on the canning jars so that you reach 240F inside the canner. As altitude increases you must increase the pounds of pressure in your canner, as directed by Colorado State University in the table above.
Go can something
In our latest video, Tricia shows you how to make grape juice in a steam juicer and then how to can it in 1 liter Weck carafes. Learn how to make and can applesauce (hot water bath) in another Tricia video; watch Tricia do pressure canning with green beans. All our videos and blog articles are based on university research. Take advantage of the local harvest in your area and can some juice, preserves, pickles, or vegetables. Follow the directions, check your altitude, can safely, and ENJOY the results!
For more canning information The National Center for Home Food Preservation is at the University of Georgia and is a gold mine of current knowledge about canning. Check us out for the basics, and for specialty jars from European makers, like Weck. If you prefer to use a book in place of online sources we have a curated collection of the best canning books.