In general, oxidation may cause foods to darken at the tops of jars. Oxidation is from air in the jars or too little heating or processing to destroy enzymes.  If enough the air wasn't driven out of the headspace, the peaches at the top can become oxidized (turn brown).

There is a difference in processing times between hot-packing (20 minute pints; 25 minute quarts) and raw-packing (25 minute pints; 30 minute quarts).  Due to altitude in Spokane County, there is also the need to add an additional five (5) minutes to published processing time.

Home canned fruit sometimes tends to float. This is not necessarily an indication of food spoilage or poor canning procedures but it can be visually disturbing. There are a variety of reasons why fruit floats:

(1) Overripe fruit - the acid and pectin content is lower. Pectin helps hold fruit in suspension.

(2)  Over-processing destroys some of the pectin. Follow the recipe using the recommended processing time (adjusting for altitude)

(3)  Packing fruit too loosely in the jar. If jars are packed too loosely or if air remains in the tissues of the fruit after processing. Pack the fruit tightly in jars without crushing it.

(4) Raw-packed the fruit.  All fruit contains air in the cells. Raw-packing is the practice of filling jars tightly with freshly prepared, but unheated food. It appears to fill the jar. During processing, the air in the fruit is cooked out. The fruit shrinks in size creating more room in the jar, allowing the fruit to rise to the top.

(5) Light syrups, juice syrups or water creates an environment in which fruit wants to equalize its sugar content with its environment. The fruit releases its own sugar, becoming lighter.

Possible Food Spoilage

In addition to the unappealing appearance, floating can contribute to food spoilage. When the fruit rises above the syrup, discoloration and drying out can occur. In extreme cases the fruit can rise and touch the lid and even dislodge the lid. Check seals before serving. Store all jars with the rings off once a seal has occurred. If spoilage has occurred dispose of the product correctly. When in Doubt, throw it out!

Information Source: https://nchfp.uga.edu/