The elderberry season out here in the bay area just ended. As I've been boiling down this year's batch of syrup I figured it's time to pass on the secrete. It's not like I'm going to be able to eat all the elderberries around here myself. :)
Mexican elderberries are a small purple berry with a heavy white bloom that grow from California down to Mexico. Other species of elderberry grow nearly everywhere in the country. You've almost certainly seen them. There in Yosemite right next to the trails. They line the Steven's Creek bike trail in Mountain View. Really they're almost difficult to avoid.
They're also fast and fun to harvest. I find two people make it the easiest, but you can harvest fairly efficiently with one as well. The berries grow in large umbras, which is a fancy-pants way of saying they grow in umbrella shapes. You can just pull off the whole cluster or parts of the cluster that are ripe from the ground. I've also been known to climb the trees and pass the clusters down. For very large ones a small knife is sometimes useful. Be sure to bring waterproof bags to put them in though 'cause they will leak juice all over your backpack otherwise.
Once you get them home you can either process them right away or freeze them as they are. No harm in either - just depends on your free time and freezer space. To process them I've found a fork works very well to pull the little berries off the sticks. Elderberry sticks are decently well documented to be poisonous so I try not to get too many into my processed berries. On the other hand there are several reports that imply boiled elderberry sticks are harmless and I have certainly felt no ill effects from the occasional rouge sticklet so don't go too crazy.
Once the berries are separated from the sticks the real fun begins. :) You can put them in ziplocks and keep them in your freezer indefinitely, bake them into a pie, or boil them down to juice. To juice them I put a mess of berries in a giant pot with a touch of water and boil them for a couple of hours. I then strain the juice through a cheese cloth. I like it with some clove boiled in it and some citrus juice added. The juice tastes like it'd be wonderful with red meat; either as a marinade or a sauce. It'd also make a good jelly. Alternatively you can boil it down to syrup.
To boil it down make sure you have put cloves and some citrus juice in (pomegranate might also work) then add honey and sugar until it's fairly sweet. Simmer it on low until it starts thickening. You can add more sugar as it boils down and you get a better sense of how sweet it will be. Once it's done boiling down put it in a jar and keep it in the frige. The longest I've been able to keep any is about nine months before it was all eaten.