“I have never made one jar of jam with pectin,” declared June Taylor, referring to the naturally derived thickener that is a staple of both industrial and home canning. (It is called for in many recipes on the Agriculture Department’s canning Web site, the National Center for Home Food Preservation, www.uga.edu/nchfp/, considered the most reliable resource.)

Pectin is present in most unripe fruits and many ripe ones, but Ms. Taylor, Ms. Mora and others consider the prepackaged stuff, available in liquid and powder form, unnatural. Some produce their own pectin as cooks did for centuries, by boiling down the juice of green apples. This is the method espoused by Christine Ferber, the French jam goddess whose tiny workshop at the eastern edge of Alsace is hallowed ground for lovers of fruit preserves. (Her jams are sold at Pierre Hermé’s pastry shops in Paris, and her book, “Mes Confitures,” begins with a recipe for green apple jelly.)

Even the pectin rebels generally follow the U.S.D.A.’s strict guidelines for canning procedures, which have become even stricter over the last two decades. “After the 1970s there was a real crackdown,” said Blake Slemmer, a lifelong canner and self-described “homesteader” in Atlanta who translates the detailed U.S.D.A. instructions into plainer language on his Web site, www.pickyourown.org.

Image Ms. Bone developed recipes using her creations, like poached pears with preserves. Credit... Evan Sung for The New York Times

“In the 1980’s there was a hard look at the science,” said Dr. Elizabeth Andress, director of the National Center for Home Food Preservation, who has worked with the U.S.D.A. for 25 years on developing the guidelines. “Canning is much safer and more reliable than when we began.” Current regulations forbid the simple open-kettle canning, in which hot food is spooned into hot jars, sealed, and left to cool. Now virtually all food must be processed after it goes into the jar, and cooks are firmly discouraged from canning vegetables other than tomatoes. (The high acidity of most ripe fruits helps discourage spoilers; most vegetables have no such natural protection.)

But experienced canners say that the warnings unnecessarily discourage novices. “You should be clean, but you shouldn’t be paranoid,” Ms. Mora said. “Imagine the conditions in which these techniques were developed.”

Although the science of preserving doesn’t change, tastes, economies and ideologies do.

Community canneries, where local farmers and cooks could once bring their produce to be canned, or do it themselves using large-scale equipment, have mostly disappeared. But in the Hudson Valley, a group in Schoharie County recently received a grant to help open a new one. Peter Pehrson, who is leading the project, said he was inspired and alarmed by the wasted produce on local farms that are geared for the commercial food market.