The Not-So-Many Uses of Dehydrated Knotweed
I have a foraging shame: The plants I’ve been calling Japanese knotweed (Fallopia japonica, or Polygonum japonica if you are an old-school genus-lumper like the King County noxious weed people) are probably actually Bohemian knotweed (Whatever x bohemicum), a hybrid between Japanese and giant knotweed (Whatever sachalinensis) species. You can tell the difference by waiting for the plants to flower and then checking the length of the flower clusters relative to the leaves.
This bit of botany has zero (0) culinary ramifications. Giant knotweed is edible, Japanese knotweed is edible, their various hybrid offpsring are edible, and as far as I can tell from reading people’s knotweed recipes they all cook up about the same.
Anyway I dehydrated a load of bike trail knotweed (Whatever x/- whatever) in April and have been experimenting with it since. After the jump, my two failures and one success, plus some gratuitous science about resveratrol and a fancy cocktail gadget DIY’d out of trash.
Failure: Oatmeal Addition
My initial idea with the dehydrated knotweed was to toss it into oatmeal. The taste was fine, and I could tell that the bulk of the knotweed had reconstituted into a nice soft goo, but the reconstituted peel had an unpleasant stringy/squeaky texture, like chewing on a bit of dental floss.
Maybe if I peeled it before dehydrating it would reconstitute with better texture. I am too lazy to ever find out.
Failure: Rapid infusion in 40% ethanol
Rapid infusion is a nice little novelty trick for fancypants cocktailcrafters. Rather than having to wait for weeks or months for flavor to migrate from your ingredients into your alcohol base, you can test out your terrible ideas in just a few minutes by pressure-cycling the infusion to force liquid into and out of the flavoring material.
This is our rapid infusion setup, which the Mr. made out of trash:
It’s a soda bottle, the valve from an old bike tube, and glue. We use a bike pump to pressurize to ~80-100psi and it works like a charm. As a bonus, depressurizing also chills your vodka a little bit so it’s ready to drink.
I tried to infuse a bit of dried knotweed and it was completely awful – it primarily tasted of over-macerated vegetable matter. I am really going to have to figure out the chemistry behind that flavor, because it keeps showing up and ruining everything.
Winner: Rapid infusion in water (Itadori tea)
I’ve been making an effort to drink more herbal tea lately. It helps that I bought myself a new teapot, with its own strainer basket rather than one of those mesh balls that likes to spill its contents into the pot if it thinks you’re looking at it funny while it’s brewing.
Itadori (“well-being”) tea is widely touted as a good source of resveratrol, which is in turn widely touted as a miracle supplement. This claim is based on an analysis of tea made from knotweed roots (Burns et al 2002 – and the authors here use the term “roots” but I strongly suspect they are actually talking about the rhizomes), which is the part of the plant traditionally used for medicinal tea in China and Japan. Meanwhile, English-language foraging blogs and sketchy herbal supplement spam-bloggers alike seem to have decided that Itadori tea ought to be made from the young shoots.
A couple things about these resveratrol claims:
- The resveratrol levels in young knotweed shoots are about a fifth of what they are in the roots.
- The resveratrol in knotweed primarily occurs as trans-resveratrol glucoside (i.e., just one of the two mirror-image versions of the molecule, and with a glucose unit tacked onto the end of it). The resveratrol in red wine occurs as a mixture of cis and trans isomers, no weirdo glucose. I am shit at biochemistry so I don’t know how this affects the metabolic pathways by which the supplement industry handwaves its outlandish claims, but the epidemiological evidence in favor of eating this (class of) molecule(s) comes from populations of red wine drinkers and not from itadori tea. Also, red wine is delicious.
- Here is a review of resveratrol effects observed in rodents; to reach the dosages used in most of these studies you’d need to drink a completely ridiculous but perhaps not impossible quantity of tea.
This health stuff is really just a distraction from the important thing: Tea made from dried knotweed shoots is very yummy and a nice way to add a little bit of tartness to an herbal tea blend. I’ve taken to drinking it in a “Seattle invaders” mix of approximately equal parts knotweed, fermented Himalayan blackberry leaves, and lemon balm.
Also, after falling into all of these Google scholar holes, I’m quite curious what a tea made from the rhizomes would taste like. I’m loath to go out with the goal of digging some up, because disturbing the root system is a good way to help propagate the plant, but I sometimes pull up a root by accident when I’m harvesting the shoots. So maybe next spring I’ll come back with a review.
- Burns, J., Yokota, T., Ashihara, H., Lean, M., & Crozier, A. (2002). Plant Foods and Herbal Sources of Resveratrol Journal of Agricultural and Food Chemistry, 50 (11), 3337-3340 DOI: 10.1021/jf0112973
- Baur, J., & Sinclair, D. (2006). Therapeutic potential of resveratrol: the in vivo evidence Nature Reviews Drug Discovery, 5 (6), 493-506 DOI: 10.1038/nrd2060