Last Friday at the N.C. Museum of Natural Sciences, I discovered some of the most awesome pickles in existence. Not only are they super crunchy, they’re also high in fiber! What more could you ask for?
Unfortunately, they probably aren’t that tasty, although I’ll admit that I didn’t get a chance to taste them. But you’d have to like to chew on wood to appreciate the taste of these, because the museum’s pickles are pickled trees.
Why on earth would you pickle a tree? you may be wondering. That, my friends, is an excellent question, and I’m glad you asked. Museum folks pickle trees as a way of preserving them so they can be put on display, or sometimes, so they can be studied later (you don’t usually need to save the whole tree for this, though).
Trees may seem like fairly durable objects, but in the museum world, things need to meet a whole new standard of “durable.” Think about a Christmas tree as an example. Fairly sturdy, right? Well … a Christmas tree that gets put up in early December usually has more fir needles than presents under it by the time Santa shows up. By the time you finally take it down, you’ll probably sweep half the tree off the floor of your living room. Now imagine you wanted to install that Christmas tree in a permanent exhibit. Or better yet, you wanted scientists to be able to study that same tree (or parts of it) in several decades. Yeah. You’d better figure out a way to preserve it.
The N.C. Museum of Natural Sciences has a huge exhibit displaying some of the ecosystems in the state. Since N.C. is pretty much entirely tree-covered, said exhibit necessarily contains dozens of trees. Lots are fake, but some have pickled branches. On a tour of the exhibit floor during Science Online last week, exhibit director Roy Campbell even pointed out one he thought was entirely pickled.
You can’t just say ”that tree is pickled,” to a group of #scio12 folks and expect to get away with it. I tracked Roy down after the conference, and he referred me to Jane Eckenrode, the museum’s exhibits project coordinator.
So how do you actually pickle a tree? Jane admits she’s not an expert, but she gave me the museum’s rough recipe:
- Make a solution of 50 percent glycerin, 25 percent acetone, and 25 percent alcohol.
- Soak whole tree branches (or even small trees) in the mixture for several months.
- Wash the pickled trees in dishwashing liquid.
- Paint the leaves or needles of the pickled tree (they turn brown while soaking in the solution).
I am enjoying imagining the size of the container you’d need to soak an entire tree, even a small one.
Why does this work? It actually turns out that there are tons of ways you can vary the recipe and still have it work. A casual Google search for “glycerin plant preservative” turns up lots of how-tos with different ingredients. The common theme, though, is glycerin or another glycol (antifreeze, for example). Glycerin is most common because it’s safe, cheap, and widely available.
When glycerin soaks into a plant through the stem and leaves (or trunk and needles), it replaces a plant’s water. Since glycerin is thick and sticky, it takes much longer to evaporate than water. This means that plants full of glycerin won’t dry out quickly like our hypothetical Christmas tree. They will still dry out slowly, but it takes a lot longer than it would otherwise.
Alcohol and acetone are commonly added to help speed things up, best I can tell from the two patents I dug up. Both mix well with water and evaporate easily, so they help drag the water out of a plant so it can be replaced with glycerin. Acetone has the added benefit of dissolving chlorophyll, which takes some of the natural color out of a plant (since it’s going to turn brown anyway). Often, that color is replaced with a dye. The N.C. Museum of Natural Sciences painted their pickled trees, but you could use a dye if you liked.
All of this begs the question, why bother? Pickling a tree — or even a branch — is a lot of work, and it doesn’t even work for all species. Pickled trees are also fairly fragile and a pain to clean, Jane tells me. In a big open-air space like the one at the museum, she said, they’d really rather use fakes. Unfortunately, there’s just not a good fake available for every species. And accuracy matters when you’re a natural history museum.
Besides, at the end of the day, don’t you think a pickled tree is just downright cool?
Huge thanks to Roy Campbell and Jane Eckenrode for taking the time to swap emails with me about this. Thanks also to everyone with the N.C. Museum of Natural Sciences who showed us #scio12 folks around, answered all of our bizarre questions, and put up with psychological experiments in the elevator.