Apparently, freeze-drying is the absolute best way to preserve all the nutritional value of the food being preserved. These could be rehydrated for food, or could be a part of an herbal tea blend.
A gentle solar dryer or other dessicator is probably the next best thing. I believe canning, as well as making fruit leather, require an amount of heat that does destroy some of the nutritional value.
I don't know what the absolute minimum safe temperature for canning is, but I suppose that it is possible to look into low-temperature canning, such that there's just enough heat to kill pathogens and microbes on the outside of the fruit, and so that when the berries and liquid cool, they vacuum-seal the jar.
Other than that, there are preserves, as jam or pie filling, but those are often a hot preparation, too.
I suppose if you froze the pies, they'd have to thaw before being devoured, so that would keep them a little longer...
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein
Could you hold this kitten for a sec? I need to adjust this tiny ad: