Aboriginal Use of the Moreton Bay Chestnut
(Castanospermum australe)
Sean McBride is a lecturer in anthropology at the University of
Queensland and teaches survival and bushcraft courses through Touch the
Wild (www.geocities.com/touchthewild/) Ph. (07) 3822 8119.
Introduction
Plant use is an important part
of Aboriginal economies. The Moreton Bay Chestnut
(C. Australe) figured prominently in the diet of Moreton Bay
Aborigines and elsewhere.
The large seeds appear to have been a staple food source, but
required processing to remove toxins.
Replicative processing experiments have been conducted
on Bungwall (Blechnum indicum) by Gillieson and Hall (1982),
and Richter (1995), but until now, not on Moreton Bay Chestnut
(except for ongoing traditional use in the rainforests of North Queensland).
Moreton Bay Chestnut
The Moreton Bay Chestnut (also known as the Black Bean
or Queensland Chestnut) is a large tree, up to 40m tall, growing
in rainforest from the Bellinger River in N.S.W. to Cooktown in
north Queensland, and up to 150km inland (Everist 1974).
It was, and is, plentiful, is
available for most of the year and produces vast quantities of large pods
containing large, poisonous seeds.
The seeds can be eaten after processing, but the
poisonous compound is as yet unknown and produces vomiting,
stomach cramps and diarrhoea. However, the Aborigines used a variety
of techniques to remove this poison.
Methods
From the ethno-historic literature I
have broken down the main processing methods into
three groups: 1) cooked first, 2) processed first, and 3)
dubious methods.
(see Table 1).
Those in the dubious section are there because of my belief that:
* Soaking a whole seed, without prior processing, will not allow
for a sufficient surface area to be acted upon by running water, in order
to remove toxins. It occurred to me that soaking the whole seed
first may have softened it, making for easier processing. I tested this
by soaking a whole seed for 4 days. It showed no sign of softening.
* Stirring the processed flour around with water, unless
conducted for a long period of time (current estimate - 18 days),
will not remove sufficient toxin, compared to using running water.
Cooking
The ground oven appears to have been the favoured method
of cooking. This method steams the seeds making them soft and
easy to process. Boiling for three hours will also produce the same
result. I have also baked seeds in a domestic gas oven for two hours
at 150O C but they develop a hard exterior that makes them
difficult to process. I suspect that `roasting' and `baking' in the
literature both refer to steaming in a ground oven.
A shallow pit, 10 cm deep and
60 cm in diameter, was prepared and lined with flat stones (not
river stones). A tipi (conical) fire was built on top of the stones, out
to the edge of the pit. The fire was lit and maintained for one hour.
The coals were scraped out of the pit and paperbark
(Melaleuca spp.) sheeting was placed on the
stones. Five kilograms of seed were placed on the paperbark and
sprinkled with 1 cup (250 mls) of water. The seeds were then
covered with more paperbark and the whole oven was covered with
soil, ensuring that heat was retained. The oven was left for seven
hours and then the seeds were removed.
Cooking has the effect of
loosening the brown, wafer-thin covering on the seeds. The covering
is removed by compressing the seed between the thumb and
forefinger of both hands, at the same time sliding the thumbs forward.
This cracks the covering making it easier to remove.
Table 1. A breakdown of the main methods of processing Moreton Bay Chestnut from the ethnographic
and ethnohistoric literature
|
Cooked first
Initial Step |
Processing |
Soaking |
Reference |
| Baked |
Cut fine with
sharp shell
|
Soaked (running water) at least 12 hours |
Roth (1901:1) |
| `Baked |
|
Baked Sliced with snail shell Soaked (running water)
"quite a couple of days"
|
|
| Roasted |
|
|
|
| Cooked in ground oven |
|
|
|
| Processed first (initial step) |
|
|
|
Roth (1901:10)
Roasted Pounded between Soaked (running water) Bundock 1885
stones 3-4 days (cited in McBryde
1978:204)
Roasted Broken up Soaked (running water) Bundock 1885
some days (cited in McBryde 1978:263)
Cooked in Sliced with Soaked (running water) Banfield (1932:260)
ground oven snail shell 2-3 days
Processed first
Initial step Processing Soaking Reference
Scraped with Soak Maiden 1898:352
jagged mussel (no other information)
shell
Cut into strips soak J.A.Boyd (in Maiden 1900:281)
(no other information)
Dubious
Initial step 2nd step 3rd step 4th step Reference
Baked soaked sliced with snail shell soaked Johnstone (1903:26)
Soaked Dried in sun roasted in hot ashes pounded Banfield (1932:260)
Baked in
stone oven pounded sifted stirred around with Colliver (1974:26)
water in a bark trough
An initial 10 kg of seeds were cooked in a ground oven in
two batches of 5 kg. The first batch, although successfully cooked,
was unable to be processed for 24 hours and in that time developed
a blue grey mould over all the seeds, which resulted in the batch
becoming unusable. The second batch was successful and did not
develop the mould, despite attempts to reproduce it.
Processing
Four methods of processing the seeds were tested:
* Grating with a jagged mussel
shell (A. pertexta). (fastest method)
* Slicing with a freshwater mussel
shell (Alathyria pertexta);
(second fastest method)
* Slicing with a snail shell
(Xanthomelon pachystylum) (third fastest method)
* Pounding between stones;
(slowest method)
The stones were used as is, but
the mussel shells and snail shells were initially ground down to an
edge, using an industrial grinder, followed by hand grinding on sandstone.
The average time taken per kilogram for collecting seeds,
preparing the fire, arranging the ground oven, removing wafer covering
after cooking, and preparation for soaking, was 17 minutes (this
did not include processing of the seeds).
One kilogram of seeds were processed by pounding
between stones. The snail shell and mussel shell were used to process
1.5kg each, and 200g were processed by jagged mussel shell for
comparison.
Times for processing 100g samples were recorded to achieve
an average processing time. The times for processing 1kg of Moreton
Bay Chestnut to a raw, inedible state prior to soaking vary from 70
minutes to 120 minutes. After processing, water was used
to leach toxins from the material.
Poisoning
The toxic effects of Moreton
Bay Chestnut on humans, cattle and horses have been
documented since the nineteenth century. According to Cribb and Cribb (1987)
"... three of the slices,
resembling a nutty potato in flavour, produced intense griping which lasted
several hours". This was after soaking thin slices in running water for
two days, then boiling for three-quarters of an hour in three changes
of water.
Queensland Herbarium records mention three servicemen in
southern Queensland in 1968, who ate small amounts of raw seeds
and became seriously ill within two hours. They were admitted to
hospital with symptoms of vomiting, severe abdominal pains and
dizziness, but recovered overnight (Everist 1974:284).
Although saponins and Castanospermine have been
suggested as possible causes of poisoning, McKenzie (1996)
states that "the toxic principle in human poisoning has not been
identified, and the effects on humans cannot, at this stage, be attributed
to Castanospermime or saponins".
My experiments produced the following results:
* Sample 1 - 100g of cooked grated seed was placed in 1litre
of water. The water was changed daily. It had a greasy/soapy
feel which remained until the 18th day (even though saponins may not
be the toxic agent they may be useful as an indicator of when to
remove the material from water). On the 18th day the seed sample
was strained and dry roasted. One teaspoonful (5g), equivalent to 11g
of fresh bean, was ingested, as this was roughly equivalent to the
three slices mentioned by Cribb and Cribb above. No ill effects
were experienced.
* Sample 2 - 420g of pounded seed was placed in a cloth bag
and left in a gently running stream, where water trickled through
it constantly. The bag was tied in place and held down by a rock
to make sure that the seed material was totally submerged. This
was the closest approximation to traditional methods, where
string bags or cane baskets were used. The sample was left for four
days (96 hours), removed, dry roasted, and again one teaspoonful
ingested. No ill effects were experienced.
Cribb and Cribb (1987:96) put a sample of seeds through a
blender, then left it in running water for 14 days, followed by baking. The
final product had no flavour, but was harmless. Much more research
is needed on the poisonous aspect of Moreton Bay Chestnut but
it appears that leaving the mashed or sliced seed in a flowing
creek for 4 days is the best way of removing the poison. Warning:
I tested the poisonous aspect on my own body which is not a
recommended method. The Moreton bay Chestnut starch that I
produced was not tested in a lab for poison content, so it is possible
that some toxins remain in this food after processing. In the interest
of safety I suggest toxicology tests be initiated on this food if you
have any interest in trying it or marketing it.
Energy returns
After the material was leached
of toxin, it was dry roasted to remove any water left over from the
leaching process. The dry weight was converted to a fresh bean
weight, and then this figure was subtracted from the weight of the initial
sample. The difference was the amount lost through leaching.
When this fresh bean weight was subtracted from the initial
sample weight, the loss from leaching averaged 52.2 % which
effectively doubles (2.09 times) the processing time per kilogram of final
product.
According to Brand-Miller (1993) the average energy return from
1 kg of Moreton Bay Chestnut is 873 kj/100gr or 8730 kj /
kilogram. If we consider daily calorie requirements we find, "a
daily 2172 calories (9014 kilojoules) ... necessary for the average adult
to sustain health" (Boyer 1986:4).
Depending on the method of processing used, the amount
of time required to produce 1kg of edible Moreton Bay Chestnut
varies from 163 minutes to 268 minutes using traditional methods.
At worst taking the longest processing time (268 minutes/kg) as
an example, the daily kilojoule requirement (9014 kj) will be
returned in 277 minutes work— roughly four and a half hours. Using the best time (163
minutes/kg) it would require 168 minute to supply daily requirements—two
and three quarter hours work. Processor experience could cut this
time down considerably.
Storage
From personal observation the seeds last for many months on
the ground. Roasted samples of leached and unleached
processed seed have been kept without refrigeration for the duration of
this experiment (three months) without any sign of deterioration.
The mould that destroyed the first batch, was I believe, a result of
the fact that the seeds were still hot and damp from the ground oven,
and left in a pile exposed to the air. The attempt to reproduce the
mould may have failed because the second sample used was smaller
and cooler when left out overnight. It appears that a dry product
will keep quite well for months.
Conclusion
As my interest in wild foods
stems from my background as an anthropologist and a survival instructor,
I consider the Moreton Bay Chestnut a good survival food
(although not necessarily in the short term) due to its abundance and high
carbohydrate content. However, a survivor would have to be
knowledgeable in the method of processing and be willing to wait 4 -5
days for any return, so perhaps for longer-term survival
processing Moreton bay Chestnut would be a worthwhile undertaking (it
obviously worked for the Aborigines).
Those involved in the bush food industry may be put off by the dangers of poisoning and therefore careful testing of the final
product would be important. Utilising machine methods of processing,
large amounts could be processed fairly quickly. Its taste is bland so
those of you in the bush food industry will have to weigh up the pros
and cons. Even allowing for a 50% leaching loss of
carbohydrate Moreton Bay Chestnut provides an abundant return, considering
its ease of gathering.
REFERENCES
Banfield, E.J. 1994,
Confessions of a Beachcomber. St. Lucia, Queensland: University of
Queensland Press.
Boyer, J.C., 1986
Capitalism, campesinos and calories in Southern Honduras. Urban
Anthropology 15:3-24.
Brand-Miller, J. ,
1993 Tables of Composition of Australian Aboriginal foods.
Canberra: Aboriginal Studies Press.
Colliver, F.S., 1974, Some
plant foods of the Queensland Aborigines. Naturalist 21(1-2):22-31
Cribb, A.B. and Cribb,
J.W.,
1987 Wild Food in Australia.
Sydney: Fontana.
Everist, S.L., 1974
Poisonous Plants of Australia. Sydney: Angus and Robertson.
Gillieson, D.S and Hall,
J., 1982 Bevelling Bungwall Bashers: a use-wear study from
southeast Queensland. Australian Archaeology 10:79-85.
James, K.W., 1983 Analysis
of indigenous Australian foods. Food Technology in Australia
35(7):342 -343.
Johnstone, R.A., 1903
Spinifex and Wattle, Queenslander, Dec.19, p. 26.
Maiden, J.H., 1898 Some
Plant Foods of the Aborigines. Agricultural Gazette of N.S.W.
9:350-356.
Maiden, J.H., 1900 Native
Food Plants, Agricultural Gazette of N.S.W. 10(4):279-290.
McBryde, I., 1978 Records
of Times Past. Ethnohistorical essays on the culture and ecology of
the New England tribes. Canberra: Australian Institute of
Aboriginal Studies.
McKenzie, R.A., 1996,
personal communication. Principle pathologist, Animal Research Institute,
Brisbane.
Pedley, H., 1992, Aboriginal
Life in the Rainforest. Cairns: Department of Education.
Richter, J., 1994, `A pound
of Bungwall and other measures'. Unpublished Honours thesis,
Department of Anthropology and Sociology, Faculty of Arts,
University of Queensland.
Roth, W.E. ,1901 Food, its
search, capture and preparation. North Queensland Ethnography 3:1-31.
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