Why shouldn't I invert my jars of grape jelly for a few seconds like my recipe describes?
The method you describe is basically "open kettle" canning, as jelly is sealed in jars with no further heat processing. Inverting the jar is supposed to destroy mold or yeast that may have contaminated the product while the jars were being filled. However, this is not a sufficient heat treatment to kill yeast and mold or to prevent spoilage. Additionally many jars will not seal using this method, making them susceptible to contamination and spoilage.
In Missouri, it is recommended that all sweet spread,
including jelly, be sealed with two-piece lids and be
processed in a boiling-water canner for five minutes to
prevent the growth of mold if you live below 1,000 feet.
Above 1,000 feet, process for 10 minutes.
Barbara Willenberg, Nutritional Sciences, University of Missouri-Columbia
Last update: Tuesday, May 05, 2009