This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
Debate has come about with respect to whether or not making wine from
elderberries can be toxic.
The short answer is NO. People have been making and drinking it for a
long time without adverse effects -- at least, not beyond the expected
ones from overconsumption. :)
If I remember correctly, you must be careful about which parts of the
plant you may use in order to avoid using the toxic parts. Use the
Elderberry wine recipes can be found, among other places, at:
Rhubarb is safe for winemaking as well, though care must be taken to
cut off and dispose of the leaves as the leaves only contain oxalic
acid which is toxic; as a sidebar, the leaves may be boiled up in water
and used as an ecofriendly pesticide.