Plum preserving/storage method that tastes like plums, not prunes (I just picked 30 lbs)

I think freezing would be your best bet - not fantastic for the texture, but when defrosted you could make a pie/cobbler or other cooked item with them. Plenty of web sites (eg http://www.fruitexpert.co.uk/using-up-a-plum-glut.html) say you can just halve them and freeze them on open tray, then when they're frozen move them into plastic bags. It's the lowest-effort option so probably worth trying on at least a fraction of your harvest.

The "fresh fruit" aromatic compound in plums is likely ethyl propionate, which has a boiling point at sea level of just under 100°C. The prominent flavor compound for prunes, according to this study, is 3-methylnonane-2,4-dione, which has a much higher boiling point of about 235°C (likely much higher than the temperatures you would reach during jam/preserve making). Therefore, to preserve the fresh fruit taste, I would recommend not heating the plums higher than 100°C. This presents a couple issues, however:

1. such low temperatures are not sufficient to preserve the plums through Pasteurization; and
2. traditional jams/preserves are set using the naturally occurring pectins in the fruit, however, pectin does not gel until around 104°C.

Here are some ideas (although I have never tested them):

• If you have access to a vacuum sealer, you can lower the required temperature for pectin to set by reducing the pressure of the mixture. Blend the ingredients for the jam in a blender and then vacuum seal. Boil the sealed bag at ~80°C, which should hopefully be high enough for the pectin to set, but low enough for the desired flavor compounds to stick around.
• Use an alternative gelling agent that sets at a lower temperature, such as agar.

Note that neither of these methods will produce a product with a long shelf life, since it was not heated to a sufficient temperature to kill off bacteria. Therefore, they should be refrigerated and eaten relatively quickly. You could also experiment with boiling the product for a short period (seconds) at the very end.

This won't be a very scientific answer, but I likewise experience an over abundance of plums every year and I am likewise not a fan of prunes.

I've had a lot of luck though turning my plums into plum sauce, rather than actual jam (not the kind you put on spring rolls). I use less sugar, no added pectin, and only cook until the plums breakdown into a mushy consistency, then can in a water bath. Absolutely delicious on ice cream, yogurt, cake, or pretty much anything.

My other solution is to use some for plum chutney, but that seems to last a whole lot longer in my pantry.

I freeze my plums. I just pit them, halve them, pack them into bags in usable portions, and freeze them. A certain number of them go into making compote or fruit spread, but as Mark A noted, the pruney flavor dies tend to come through then. Freezing does not produce that effect, so when I use plums from the freezer for cakes and the like, they have a fresh, light taste instead of the heavier, back-of-the-throat prune taste.

Warning - this is a somewhat speculative answer, I haven't actually checked these methods for fresh plum vs prune taste, just logic'ed that they might work - especially given Mark A's answer about the boiling point of the relative flavor compounds.

A while ago, I saw a method of preserving strawberries that talked about the flavor differences from fresh to cooked preserves (jams and such). I don't know if the method used there will work for plums, or if the results will be similar using plums instead of strawberries - but it might be worth trying and at worst, might suggest a place to start looking for similar "uncooked" preserves specifically targeted at plums.

So this particular historical preservation method used unblemished fresh strawberries, cut up, sugar, and chopped up raisins - in a ratio of three parts (by weight) strawberries, to four parts sugar, to one part raisins. The raisins are used as a sort of preservative, and the recipe makes a kind of sweet pickled strawberry - they layered the sugar, fresh strawberries, and raisins in a covered jar, stored in a cool place for up to several months (for safety reasons, refrigerator would be wise nowadays) and over time the strawberries released enough liquid to cover the fruit with a thick syrup. The strawberries ended up a bit tougher and more dense (partly dehydrated, after all) but the flavor profile was apparently closer to "fresh" then "cooked" strawberries.

So, while I'm not sure of sugar and raisins will preserve your plums flavor in quite the same way, you can certainly look for sweet plum pickle recipes, or look into storing them in alcohol, or other sorts of uncooked preserves, and you can store these in the fridge or freezer if you want to be careful. The flavor will be more different the more other things you add, but you might like them anyway.

Another possibility might be to look into candying or crystallizing or glaceeing your plums - or making a mostarda, if you want, with the addition of mustard oil or powder - prick them all over, keep them in concentrated sugar syrups, and keep filtering out, reducing and replacing the syrup and letting the plums soak - I should note you want the old, slow method of soaking and reducing just the syrup and soaking some more, rather than the quicker method of repeated simmering if you don't want the plums to taste cooked. Over time, the water will leech out and be replaced by sugar (and be reduced out of the syrup), leaving you with a batch of shelf-stable candied plums. Again, since the plums aren't cooked, you should get more of the fresh plum flavor than the prune flavor. Find a good recipe for this, though, it takes a known recipe with good ratios to be safe leaving sugar syrup and fruit at room temperature for weeks or more.

Have you tried adding a strong acid medium like whey, kefir or wine/vinegar that might speed up the pickling process? Also, I'm not sure what cooking them will do to the flavor.

I have heard that adding oak leaves to pickles will keep them crisp...maybe there's something like this for plums to keep them tart.

Does store bought plum jam taste like prunes as well?

Sorry for not providing any solid answers...I hope my thoughts have sparked a light bulb.