Water bath or pressure canner?

Clostridium botulinum is a bacterium whose spores live in soil and on garden produce, harmlessly, until they find the one place they like: a sealed jar with no oxygen, low acid, and room temperature. The spores survive boiling — 212 °F does not kill them no matter how long you hold it — so a jar of plain vegetables that came out of a boiling-water bath can look, smell, and taste perfectly fine while the spores wake up inside it and release a toxin that is among the most poisonous substances known. There is no smell, no bulge you can count on, no taste. Two things stop it: heat above the boiling point, which is what the roughly 240 °F inside a pressure canner provides, or acid at pH 4.6 or below, which is why fruits, tested pickles, and acidified tomatoes are safe in a water bath.

That is true in a great many families, and it is not evidence that the method works. Botulism is rare — rare enough that a household can water-bath beans for decades and never meet it — and the jars that did go wrong got thrown out for looking odd, with nobody connecting the dots. Not being harmed is not the same as being safe. USDA and NCHFP publish no boiling-water process for plain green beans, at any time, because none was ever validated; the only tested processes for them are pressure processes. Keep her recipe, keep her jars, keep her hand for salting — and change the canner.

Only where a boiling-water bath would have been allowed, and only inside NCHFP's published limits. An atmospheric steam canner is not a pressure canner and is never an option for low-acid foods. NCHFP accepts it for naturally acid or properly acidified foods with a pH of 4.6 or below, using a research-based recipe's process time adjusted for altitude, and states that the process must be 45 minutes or less including any altitude adjustment. The published conditions also require that the air is vented out so the canner is running on pure steam at the temperature of boiling water, that jars are preheated before filling, that the canner is not opened during the process for any reason, and that jars cool in still air rather than being cooled faster. Outside those conditions, use a boiling-water canner.

No. NCHFP states plainly that it does not support the use of USDA canning processes in electric multi-cooker appliances carrying "canning" or "steam canning" buttons, even where the manufacturer's manual gives canning directions. The published reasons are worth knowing: no USDA thermal-process work has tracked the actual temperature inside jars in an electric cooker; reaching a pressure reading does not prove the food inside the jars got hot enough, since jar position and steam flow change how heat arrives; a power surge or dip gives you no way of knowing the temperature fell; and a small cooker cools too fast, losing heat that the tested process counts on. USDA processes were determined for stovetop pressure canners holding four or more quart jars standing upright — use one of those.

No. Altitude changes the numbers, never the method: a low-acid food is low-acid at sea level and it is low-acid on a mountain. What altitude changes is how you run the canner. In a boiling-water bath you add minutes by band — at about 5,000 ft, that is 10 extra minutes on the recipe's time, using the 3,001–6,000 ft band. In a pressure canner the processing time does not change at all; the pressure does — 15 lb on a weighted gauge and 13 lb on a dial gauge at that same elevation. Look up your town's adjustments, or adjust a recipe's time.

Not on your own. Tested acidified recipes do exist — pickled beets, pickled beans, tested salsas — and in each one the amount of acid, the amount of vegetable, the jar size, and the process time were tested together as a whole. The acid was measured against that specific load of food. Splashing vinegar into a jar of plain green beans changes the flavor and not much else: nothing tells you the finished pH landed below 4.6 throughout the jar, and pH is the whole safety margin. Follow a tested pickling recipe exactly, or pressure can the plain food.

Treat it as low-acid until a tested recipe tells you otherwise — that means a pressure canner, and it means finding a tested process for that food rather than borrowing one from something similar. Mixed dishes take the method of their most demanding ingredient: a tomato sauce with meat or with pureed vegetables in it is a low-acid food. Your county extension office will identify anything unusual, and NCHFP publishes directions food by food. If no tested process turns up, the honest answer is that the food belongs in the freezer.