Tools and Techniques- Canna Flour

A big emphasis in home gardening is on vegetables. Home grown ones often taste great compared to those in the shops, there are loads of different types to try, and they tend to give the biggest economic reward compared to store bought. A dedicated and skilled home gardener, using large inputs of manure, mulch and irrigation can produce impressive amounts of food from a relatively small space. By comparison if the same skilled gardener grew a starchy staple crop like potatoes the yield would still be impressive but not as high in comparative volume, value and quality compared to their store bought equivalent. If they were to be even more dedicated and grew a grain crop they would be even more disappointed with both the size of their harvest and the relative value and quality compared to store bought.

The key though lies in the relative water content of the different forms of produce. Dry grains when cooked will swell to many multiples of their size and contain highly condensed energy and nutrients. The potatoes by comparison are about 80% water, while that juicy lettuce is more like 96% water and likely 50% air by volume for frilly types. Dry wheat only contains 12% water by comparison. Just eyeballing the volume of produce coming from a garden can be completely misleading as to the nutritional value. In a world where a bag of rice that will feed a family for a week costs a few dollars it makes sense for people to take life sustaining staples for granted, especially when at the same time a single lettuce costs more.

As a zero input grower with an interest in our post-industrial future I like to put a lot more emphasis on starchy staples than most home gardeners. In our humid coastal zone with unpredictable rainfall and swarms of birds of more species than I can count growing grains as a staple crop is more miss than hit. Staple crops need to be reliable or are worse than having nothing since you can put a lot of work into growing a large crop only for it to fail at harvest. Tuber crops perform more reliably in humid places and one leading contender is the humble Queensland arrowroot, Canna edulis. I will do a full plant profile on them shortly but wanted to outline how I use this incredible crop.

The tubers of arrowroot can be eaten whole much like other root crops. They can be variously boiled, mashed, roasted etc. People eating them this way normally find them a bit overly firm without being crunchy, bland without being either offensive or admirable, remark that they were nice enough to eat (especially when drowned in bacon or cheese) and then go on to never eat them again. Rats, ducks, geese and bandicoots will also nibble at the roots a little during hungry seasons and then usually not come back as well.  People can’t explain where this aversion comes from but I suspect there is some kind of anti-feedant chemical in the roots, as are found in any starch storing plant. Luckily there is a way around this issue that opens up a whole new set of possibilities.

Arrowroot has the largest starch grains of any plant, making it very easy to separate from the rest of the material in the roots. The roots are best harvested in winter when they swell up full of starch as the plant goes into dormancy in early winter. If you wait until the new shoots emerge in late spring then the yield will drop significantly. Roots can be crushed or grated, with the finer sized holes in a common cheese grater working well enough. Peeling the more fibrous outer skin with a vegetable knife makes grating go easier while also removing any dirt and revealing damaged tubers before they go into the mix. The tubers are quite firm and easily damaged, causing bruises to spread through the tissue. This makes the tubers difficult to store and transport whole so only harvest as much as you can process immediately. Luckily the tubers store well when the whole plant is left in the ground. I piled up the grated material in a bowl with a bit of extra water as I went. The white roots quickly turn a peculiar shade of beige on exposure to oxygen, likely a similar reaction as found in an apple that browns after being cut.

For small scale starch extraction the following method worked well for me. Using a coarse sieve or pasta strainer a couple of handfuls of grated roots are taken each time. The strainer is placed in a bowl with enough clean water to come up into the strainer a few centimetres. This allows you to mix the water through the grated roots, allowing the starch grains to drop out into the bowl. I found giving the wetted grated roots a light squeeze, a second fluff and shake in the water, and then a tight squeeze was enough to remove almost all the starch. I did a test second extraction on the pulp and yielded only a small amount more and wasn’t worth the time. You can feel the starch grains in the water around the root pulp as a kind of silky sliminess that disappears after washing, making it easier to squeeze the pulp thoroughly. Once this process is completed I stir the accumulating starch sludge layer on the bottom to get it back into suspension and filter the mix through a fine sieve to remove smaller fragments of debris. After sitting for ten minutes all the starch will form a thick layer on the bottom of the bowl, allowing you to pour the liquid off the top. A layer of flecks of debris will be present on top of the starch that can also be carefully poured away. After I combined a few batches of starch sludge I repeated adding water, allowing it to settle, then pouring off the brown liquid and a little debris to clean the starch. The starch sludge was then drained thoroughly and tipped into a few baking trays for drying. Once the material was dry to the touch after regular stirring in a day or two the flour was dried in an oven at under 100 C with the door ajar until it crumbled to dust. It is important not to heat the flour until it is fairly dry or it can start cooking and swell, making storage difficult. I will outline a few ways to use the flour in future posts.

Once extracted and dried the arrowroot flour represents a highly stable form of staple energy that can be kept almost indefinitely. By comparison sweet potatoes store about a month, potatoes about three months and brown rice about six months before flavour declines. In our humid and unpredictable climate this represents a potentially crucial resource to keep people fed during prolonged droughts or crop failures. The crop in question represented about 15 kg of tubers, half the yield from a space about 2 x 2 m. That 15 kg of tubers produced about 0.5 kg of starch (I will weigh it once dry and update the entry). By comparison fresh potato contains about 18% starch, similar to canna at 12-16%, relative to canna yielding about 3.5 % pure extracted starch from this basic method. The left over pulp still contains a lot of starch and makes good animal feed, with my chickens taking to it readily. Grinding rather than grating should increase yields.

Starch contains 17 kJ/g in energy, so a human needing about 10 000 kJ per day would need about 600 g of starch if that was their entire diet (obviously not sustainable since it would contain no other necessary nutrients, but useful as an upper limit). If the starch crop produced today was to represent 50% of a person’s diet then the approximately 500 g yield would last for two days. Processing the starch took about four hours (mostly tedious grating), a job that should take half as long with better equipment. Growing the crop probably took an hour maximum. As such it should take around three hours to produce one day’s worth of energy (supplying 50% of total energy needs). With 12 useful hours in the day, this means one quarter of the day would be spent gathering this food energy. Such a lifestyle would have a time equivalent energy return on energy invested of about 4, slightly above subsistence levels but too low to support complex societies. Further improvements in processing yield and speed would potentially push this to about 10, a level more in line with other subsistence staple crops. In terms of space requirement a human consuming 50% of their energy from arrowroot would need about 730 square meters of the crop, or a bit under a quarter of an acre. Keep in mind this particular plant was three years old, so the person may actually need three times as much space in rotation, so more like ¾ of an acre per person (and still only supplying 50% of total energy, so more space would be needed for more diverse food types, plus space for maintaining fertility and all their other needs, so my usual estimate of 5 acres per person seems consistent with this crop).

Despite the relatively low return on investment arrowroot has some important advantages over other crops. It continues to soldier on, growing larger for years through periods of drought and flood. It grows on shallower soil than many other crops with no added fertility. And most importantly it can be turned into a highly stable product with very primitive technology, providing a rare form of long term stored energy to even out the inevitable bad seasons.

An overgrown and dormant clump of Queensland arrowroot, three years old.

Half the tubers from the clump, about 15 kg. Old and small tubers were rejected.

Grating station showing peeled and unpeeled tubers.

Washing station with white pasta strainer doing a great first separation.

Chickens sampling the washed pulp that still contains half the starch.

Final rinsing. The texture of the settled starch is similar to cornstarch and water (oobleck)

Chunks of pure starch spread out to dry with regular stirring.