Which technique is used for preserving fruits in jars with sugar?

The technique used for preserving fruits in jars with sugar is canning. This method involves placing fruits in a jar with added sugar, often along with water or juice, and then sealing the jar to create a vacuum. During the canning process, the jars are heated, which kills any bacteria, yeasts, or molds that could lead to spoilage. This not only preserves the fruits but also enhances their flavor as they soak in the sugary syrup. The sealed environment of the jar prevents air from entering, further extending the shelf life of the canned fruits.

In contrast, freezing is more about storing fruits at low temperatures to slow down the enzymatic processes that cause spoilage, but it does not necessarily involve sugar or jars. Dehydrating involves removing moisture from fruits, which can also preserve them, but this doesn't typically involve sugar or jars in the same way as canning. Pickling refers to the process of preserving food in a solution of vinegar, salt, or sugar, which differs from the primary focus of canning fruits in a sweet syrup. Thus, canning is the most appropriate technique for preserving fruits in jars with sugar.