What technique is used for preserving food by heating it and then sealing it in jars?

The technique used for preserving food by heating it and then sealing it in jars is canning. This method involves placing food in jars and heating them to a temperature that kills bacteria, yeasts, and molds, which helps to prevent spoilage. The process creates a vacuum seal as the jars cool, which keeps the food safe from contaminants and extends its shelf life.

Canning is particularly popular for preserving fruits, vegetables, and jams, as it allows for a long storage period while maintaining the food's flavor and nutritional value. By using proper canning methods, such as the water bath or pressure canning, it ensures that food can be safely stored for months or even years, making it a practical choice for both home cooks and commercial operations.