Extracting starch from bracken - an experiment

I made a thread on the possibilities of bracken for food here. Many people know that the fronds are fairly edible (although proper preparation is advisable because of possible carcinogens) but not so many realise that the roots contain an edible starch too. This video shows a family extracting the starch and preparing noodles from it:



My research indicated that the carcinogens are likely to be least in the winter. Almost all the videos I saw seemed to involve digging the roots after the fronds had completely died down, so early February, before the plant gets going again seemed to me to be a good time to be trying this out.
Because we don't have enough growing on our land to be worth digging I asked a neighbour if they minded me digging up some of their bracken; not surprisingly they were very happy for me to dig up some of their weeds The roots form a surface mat with lots of growing points, and a few inches underneath, larger smoother roots are found. I tried to clear the patch properly for them, so did have some of the more branched surface roots, but it didn't take long to dig up a couple of bags full of roots to play with try and make starch from.

putting roots in the burn to wash

So I got the roots home and washed them. I estimate that I had about 12 kg of roots. I admit that I didn't scrub every root with a brush, just rubbed them under water until they looked pretty clean.

roots after washing

I have an apple crusher, which I thought would be ideal for crushing the roots. In actual fact it didn't turn out that easy. The roots were very woody, so turning the handle to break them was quite hard. They also wrapped around the axle and some posted right through with minimal damage. I fed them though twice.

new use for apple crusher

I still wasn't happy that the roots were well crushed, so I did end up bashng them pretty thoroughly with an old rolling pin.

kitchen tool abuse

The Chinese videos I found mostly used large pestle and mortars, although at least one used some sort of electrical macerator. The Maoris ate bracken root as a staple of their diet until late in the 19th century, and bracken is part of their mythical history. There are lots of wooden clubs, apparently used for crushing bracken roots in various collections and museums. I'm not clear what the surface they were bashed against was though. The roots may have been cooked before beating and extracting the food. Also I believe the bracken in New Zealand is a slightly different variety, being rather larger than the bracken found elsewhere.

Anyway, the roots did become quite gelatinous, although flakes of white were still adhering firmly to the roots like coconut flesh.

white stach on bracken root fibre

(to be continued...)

Rubbing the roots between my hands with some water seemed to remove some of the starch, although the water didn't become really cloudy. I fished out the sticks and filtered the water through a fine net curtain. Since it was freezing out, I did all this in the bath - makes a mess!  

filtering starch from bracken root

The resulting liquor was three buckets of liquid that looked like tea without enough milk:

three buckets of 'cold tea'

Left over night I had three buckets of water with a layer of sludge at the bottom. Hmm... Looks like bracken starch is very close in density to my native silty soil. There was a little white in there, more than you can see in these pictures since it mostly was underneath the mud.



So I rinsed the mud out of the three with more water into one bucket and ended up with a bucket that still looked very much like British Rail tea.

second rinse put to settle

I must admit at this point I was wondering whether I would get anything like starch at all!

edit -mistypes, doh!

After another day settling I thought I could see a starch layer!

combined bracken starch layer second rinse

When I tipped out the water however, it looked like mostly mud with some starch underneath



So I added more water to rinse it, and put it on to settle again in a narrower jar to try and get separate layers - looked more like chocolate now!

bracken settling - third rinse

bracken settling - third rinse starch layer?

This time I scraped off the top settled layers separately which seemed to consist of mostly mud. I could feel that the wet starch has that thixotropic nature that fine cornflour has.

separating off most of the mud

I rinsed the best bit that seemed to be mostly starch, and put the liquid through a finer cloth, in the hope it would filter off more of the mud:

fine cloth filter for bracken starch catching mud

I've since rinsed this twice more but am still getting mixed results. The liquid is still quite chocolatey in colour and, although it looks like it is mostly starch against the glass, when I remove the sludge it is rather more mud than I feel happy ingesting.

nice starch layer after another rinse

still lots of mud

I've rinsed and got it settling again, but don't feel I'm going to be able to separate enough of the mud out for a good result.

Very interesting. We have loads of bracken here (Southern Gulf Islands just off the West Coast of Canada). I'll be honest that the carcinogen warnings have scared me off eating them, especially since we get lots of asparagus and nettle tips that time of year so aren't really in need of greenery. I've had a lot of success getting starch as a by product from cold leaching acorns, but never heard of bracken root. I hope you're able to get something from all your hard work!

This is indeed interesting.

I've been thinking about this, and I don't think the mud layer is actually mud; those roots looked pretty clean in the pictures.  It looks like some kind of oxidized plant goop, like maybe a sap or latex-like secretion from the skin.  

If I were to do this, I'd put the initial batch of liquid in something kind of wider and shallower (like a dish pan/ basin/ even a square plastic tote, as long as the bottom was flat) and let it settle overnight, then pour off as much water as I could and use a really flat spoon or even a putty knife to scrape that brown layer off.  If the goop scrapes off cleanly, you wouldn't need to do another rinse and settle.

I've never tried anything like bracken, so far I've only got starch from beans (failed tofu experiment) and sweet potatoes.  I do watch a lot of Chinese youtube though, and processing starches is popular subject matter, so I'm an armchair expert ;)

If the brown stuff is actually "mud" (fine silt, clay, other mineral matter?), shouldn't it be heavier than the starch, and settle first? Unless of course the "mud" particles are significantly smaller than the starch particles. Although I guess the fact that the starch sinks at all, and in *roughly* the same time frame as fine silt or clay (?) indicates it has similar weight. I have no idea how to begin researching particle size and weight for what presumably is not the most well known type of starch, but if someone here has any relevant experience that might be one way to find out what the different layers are. You could maybe also try to get a reasonably pure sample of the suspected mud and burn it, if it turns to ash it will at least be something organic rather than actual silt or clay.

I'm pretty sure that the brown is mud. I think at this small scale strange things start to happen - surface effects and molecular attractions become more significant. I looked up some starch dimensions:
ref

since silt particles are 4-40 micrometres, and clay are 1-4 micrometres these are in the same ball park as the starch particles seem to be. I'm finding that the starch behaves like UK cornflour (maize starch) in it's thixotropic behaviour so i'm guessing it is a similar size.
I think there is some sort of static effect, since I was getting a white layer against the glass, which seemed to be a falsely optimistic reading of the purity of the starch. When I tilted the jar as it settled I did get a better separation, but it may just be that the substance is getting purer. I also looked at the magnetism (my soil is derived from basalt rock which can be quite magnetic. Although some particles were attracted to the magnet, much was still just mingled in the starch.
(see images attached below)
I have however started to get some separation, and I think that the key may be just to have far more starch than silt! Cleaning the roots better - using fewer of the thin roots and more straight ones that are easier to clean perhaps - is probably going to make a small difference too.
I've also been reading up about how the Maoris processed their root starch  (Maori ancestral knowledge site)and they seem to dry and then pound the roots, so this is something I can try. Also harvesting at different times of year; again the Maoris are reported to have harvested in summer or Autumn rather than winter, and it maybe that the starch is more easily dislodged at different times of year.
I think I have reached the point of diminishing returns for this batch, but there is definite promise there if can get the technique right. After about 10 rinses and settles I have probably got a couple of table spoons of something that I could cook with!

I'm curious, Nancy, are you mostly playing around to satisfy your curiosity or are you after an income stream for your homestead? You mentioned in your earlier thread that the starch sells for £100/kg...

Hi Christopher, Seriously I'm just playing! I don't think I'm likely to bother set up a business, even if I do crack the bracken starch refining process. It is an interesting theoretical possibility though I think. In the UK bracken is an invasive weed, and people do get paid just to cut it at the moment. It's always nice to find a benefit out of a problem.
On a commercial scale I guess you'd want something like a potato harvester that would lift the roots, maybe a jet wash to wash them, mincer to macerate them, then whatever filter and cyclonic separator might be appropriate for the final stages of cleaning. Drying the starch would be needed and then packing and storage/selling.

Interesting.  I suspect highest starch content will be at late summer or early fall, maybe before the fronds die back.