The National Center for Home Food Preservation, a USDA-supported center based at the University of Georgia, keeps a short list of canning methods and tools that home canners should leave on the shelf. Its “Equipment and Methods Not Recommended” page, checked Nov. 11, 2026, covers 10 practices and pieces of gear, from open-kettle canning to so-called canning powders.
The list matters most in fall and winter, when home canners are working through late harvests and holiday gift jars. One entry, steam canners, now carries an update that allows them for acid foods under strict conditions, and the details are below.
1. Open-Kettle Canning
Open-kettle canning means pouring hot food into jars and sealing them without any further heat processing. The National Center’s list of methods not recommended puts it first, saying the practice does not reliably stop spoilage. A lid that pops down on a hot jar is not proof that the contents were processed.
Produce that will not be canned by a tested method still has other routes to the pantry; Frenz Hub’s guide on how to freeze fresh green beans is one example of a method that skips canning entirely. Gardeners bringing in late crops from elevated garden beds or a windowsill full of kitchen herbs that keep growing all winter can freeze or dry what they cannot can by a tested method.
2. Ovens, Microwaves and Dishwashers
The center also rules out processing freshly filled jars in conventional ovens, microwave ovens or dishwashers, for the same spoilage concerns. None of these appliances delivers the controlled, tested heat that a boiling water canner or pressure canner provides. Kitchen appliances have changed home cooking in big ways, as a recent look at the kitchen appliances that changed how American families cooked shows, but none of these three is a canner.
3. Steam Canners, Unless Every Control Is Met
The original entry said steam canners were not recommended because processing times were still being researched. The center later added an update: after research led by Dr. Barbara Ingham at the University of Wisconsin, it says atmospheric steam canners can be used for acid foods as long as certain critical controls are kept.
According to the center’s steam canner guidance, the food must be naturally acid or properly acidified with a pH of 4.6 or below, and a research-based recipe must be followed. The canner must be vented of air before timing starts, the steam must stay at the temperature of boiling water throughout, and processing time must be 45 minutes or less, including any altitude adjustment. The canner cannot be opened to add water during the process. Steam canners are not pressure canners and are not for low-acid foods.
4. Pressure Above 15 PSI
The center says it does not recommend applying pressure processes above 15 PSI when using new pressure canning equipment. Canners should run their equipment at the pressure given in tested directions rather than turning a gauge higher as a shortcut.
5. Canning Powders
So-called canning powders “are useless as preservatives,” according to the center, and they do not replace proper heat processing. No powder or additive turns an untested method into a safe one.
6. Jars With Wire Bails and Glass Caps
Jars with wire bails and glass caps make attractive antiques or containers for dry ingredients, the center says, but they are not recommended for canning. Shoppers who pick them up at estate sales can still use them in the pantry; Frenz Hub’s tips on seasonal storage cover ways to keep that kind of glassware organized.
For canning itself, the center’s page on recommended jars and lids says regular and wide-mouth Mason-type, threaded home-canning jars with self-sealing lids are the best choice. Jars can be reused, but each use needs a new flat lid, while screw bands can be reused if cleaned, dried and stored properly.
7. One-Piece Zinc Porcelain-Lined Caps
These older caps are no longer recommended, according to the center. They show up in vintage collections and family basements, but they are not part of current tested canning procedures.
8. Zinc Caps With Flat Rubber Rings
The same goes for zinc caps that use flat rubber rings to seal jars. The center lists them alongside the porcelain-lined caps as closures that are no longer recommended. The two-piece system of a flat metal lid and a screw band has replaced both.
9. “Dry Canning” Vegetables Without Liquid
One method circulating online involves packing raw vegetables or other food pieces into jars without the covering liquid used in the tested process. The center says this can lead to under-processing, and for vegetables it raises the threat of botulism.
A Preserving Food at Home post describes the practice as putting raw corn, green beans, carrots or beets in jars with no added liquid and pressure canning them for the same time as the tested method. The post urges canners to stay with properly researched and tested procedures.
10. Oven “Dry Canning” of Dry Foods
The term “dry canning” is also used for heating dry foods such as grains, beans and nuts in canning jars in an oven for storage. The center says this is not a science-based method of storing dry foods.
Home canning is the process of packing foods such as fruits, vegetables and meats into glass jars and heating them to create a vacuum seal and stop spoilage organisms, according to Wikipedia. The center notes that its tested processes are meant to be used together with the food preparation and jar-filling directions in each recommendation, and that it will take time to fold the steam canner update into the USDA Complete Guide to Home Canning. Until then, its online pages are the most current word.
This article was produced with AI assistance and edited for accuracy against the sources linked above.
Image: Nutrition, Food Safety & Health – CC0/Wikimedia Commons
