Date palm sap

The date palm sap stores the bulk of its reserve of photosynthetically produced carbohydrates in the form of sucrose in solution in the vascular bundles of its trunk. When the central growing point or upper part of the trunk is incised this palm sap will exude as a fresh clear juice consisting principally of sucrose. Upon standing and favoured by the warm season (when tapping takes place), breakdown of sucrose will soon commence, increasing the invert sugar content, after which fermentation will set in spontaneously by naturally occurring yeasts and within a day most of the sugar will have been converted into alcohol (around 5% v/v). The liquid will turn milky white. References to palm tapping date back long before the birth of Christ and also the famous Roman chronicler and historian Plinius makes mention of it.However, the curious fact exists that, traditionally, tapping of the date palm has not developed in all date producing countries, apart from enforced bans on tapping that have been imposed, be it on religious grounds or to protect a national food source. Palm tapping, even if still existent in several parts of the date producing world, has always been marked with two phenomena: a potential danger of abuse of and addiction to the fermented sap, and a consequent decline of a recurrent food supply. With regard to the latter point it should be emphasized that tapping a palm, especially according to the methods used in the date producing countries, is a severe intervention. It deprives the palm of most of its (productive) leaves and food reserves and to recuperate these losses it is knocked out for at least 3 or 4 years before it will bear a full crop of fruit again. A severe wound inflicted on the palm is kept open every day to maintain the sap flow. The palm's survival depends on the skill of the tapper (Usta) because if the daily scarring is carried on too far, the palm will die. Literally the palm's life balances on razor's edge (in this case the Usta's sharp sickle) and it adds a sentimental issue for some people who resent seeing a palm exploited to these extremes. If not forbidden outright by Governments, the authorities have attempted to regulate palm tapping by restricting measures such as for example: i: subjecting it to a permit, ii: imposing tax, iii: permitting tapping of only diseased, declining or poor yielding palms, iv: authorizing only registered tappers, v: marking and wiring of palms, vi: restricting the period of tapping to 60 days, vii: obligatory substitution of the tapped palm by a new palm, viii: imposing heavy fines and/or imprisonment of trespassers . These measures may assist in preventing a deterioration in date palm cultivation, but they fall short of preventing consumption or abuse of the fermented version of palm sap.

It is indeed not an easy task for the legislator to intervene in the consumption of a liquid derived from a natural juice for which he gave permission to be harvested and which spontaneously has changed its properties within a matter of hours. The fact that the natural (sweet) and the fermented juice in Arabic are known under the same name, lagbi or lagmi, does not simplify the matter either.

It is generally agreed that palm tapping can have, potentially, undesirable side effects and the safest way to prevent these from happening is to prohibit it altogether, a measure that more than often has been applied.

However if one looks at the thousands of tons of sugar produced from the Wild date palm (Phoenix Sylvestris), the Coconut palm, Palmyra, the Sago (Caryota Urens) and the Nipa palm, the question is raised whether sugar from date palm sap would under certain circumstances not be profitable. Or put in another way: the date palm offers its "produce" in two ways, as fruits and, alternatively, as a sugar (sucrose) containing sap; does a choice exist?

Compared with the Indian experience where tapping the Wild date palm is a very well developed cottage industry, two points emerge immediately: the Wild date palm does not offer an alternative product because its fruits are not attractive for human consumption hence it is not a choice anymore; secondly palm tapping has developed in India in a much less drastic way. It is done annually and it does not remove the whole crown of leaves, thus leaving a great part of the productive capacity of the palm. To illustrate the differences further both methods of tapping are briefly described

Comparison between Indian Method of tapping the wild date palm (Phoenix Sylvestris) and tapping the date palm (Phownix Dactylifera) as practiced in some date producing countries (Local Method)

LOCAL METHOD

INDIAN METHOD


a) Preparing the tools


a) Preparing the tools


b) Removal of leaves


b) Removal of leaves


 
c) Cleaned tapping surface


c) Cleaned tapping surface


d) Cover with sheath


d) Make incision


e) Inserting the spout


e) Inserting the spout


f) The collecting pots are hung


f) The collecting pots are hung


g) (Twice) daily juice collection, changing of pots 
and periodically renewing the cut


g) (Twice) daily juice collection, changing of pots 
and periodically renewing the cut

h) - Partially fermented sap (left)
    - Sap froma limed pot (middle)
   - Clarified, filtered sap (right)

 

i) Indian stove under construction

j) Adding phosphoric acid to haeted limed juice

k) Measuring PH with PH paper

l) Filtering the neutralized juice

m) Cleaning the pan

 

Palm tapping as practised in some of the date producing countries consists of removing all the leaves except some of the outer circle to give support to the tapper whilst working. The top of the trunk is cut in a cone shape, carefully leaving the terminal bud intact. At the base of  the cone a canal is cut around it, in which the juice oozing from the cone is collected and guided via a spout made of the leaf midrib into an (earthenware) jar, hung on the side of the palm. The cone is protected from the sun against drying out, by an inverted basket or by palm fibre. The flow of juice starts slowly but may reach full capacity after six or seven days. Twice daily the tapper will climb the palm to collect the juice and to shave a thin sliver of tissue of the cone's surface to keep the vessels from drying up. Whilst this daily process is going on, the terminal bud is growing upward also and every 20 days or so a readjustment of the cone, canal and spout implant has to be made. As in most cases, if not all, this tapping method is used for an eventual fermented beverage, no precautions are taken to keep the yeast population down as is done in Indian tapping. On the contrary some of the earlier (already fermented juice) may be left in the jar as a starter to hasten the process for the newly collected juice (the yeast accumulated from lagbi was also used as leavening agent in breadmaking in Tibesti). Length of tapping period largely goes by the individual character-istics of the palm and cases have been known of up to 3 or 4 months. However, the law has usually put a limit to that in order to prevent too much exhaustion and a risk of high mortality amongst the tapped palms. In terms of yield (both in total litres and kgs of solid matter) only indicative figures can be given because several factors are determining such as variety, age/height and location (e.g. water supply). From comparative tapping tests between the local and Indian methods some actually measured results for the local method are given all palms were located in the same area

Variety

Known as

Palm height
(grnd level to terminal bud, m)

No. of tap.days (x) dried up (o) ongoing

Yield in l.

Yield in solids (kgs)

Solids 
(% age)

Average
juice/day (1)

Average solids/day (kg)

Limsi
Limsi

exc.
yielder

3.40

3.50

42 (o)

45 (o)

352.1

397.6

35.9

47.7

10.1

12.0

8.4

8.8

0.85

1.06

Bikraari
Beyuudi

good
yields

5.80

7.20

41 (x)

52 (o)

400.1

732.2

44.7

62.3

11.2

8.5

9.8

14.1

1.09

1.20

Hammuuri

 

5.30

46 (x)

268.1

32.7

12.2

5.8

1.00

Aami
(seedling)

poor
yielders

8.20

39 (x)

229.3

36.9

16.1

5.9

0.95

 

 Palm sap yields:
 

Together with the (scarce) literature references  major conclusions on yield for the varieties recognized as the more adapted for tapping are that:

  1. Total yield in litres for one tapping period may easily reach 500 l but higher yields are known (1,212 l in one particular case

  2. A daily yield of 8-10 l is an acceptable range as an overall average

  3. The average solids contents of the juice is around 10%, with higher levels possible but these are mainly due to lower moisture excretion.

  4. The daily yield of solid matter (mainly sugar) turns out to be rather constant for the different palms and amounts to about 1 kg/day

Apart from quantitative appraisal there is also a qualitative appreciation of the juice and there are varietal preferences.The tapping operation eventually will leave a scar on the trunk in the form of a circular indent . By the number of those rings one can tell how many times a palm has been tapped, normally not more than once every 5 years. A number of six rings is seldomly seen, but three and four is rather common. In this respect it should not be forgotten that each ring adds another relatively weak spot in the trunk and the risk for the tapper proportionally increases.

 Effect of Palm Tapping on 
Trunk Development (Local Method)

 

After tapping is finished in March the cut surface will dry out and heal but leaving an indent in the trunk. The next cut will be made on the other side of the trunk (180° ) a little higher because the palm has grown, and leaving again a similar scar. Eventually after several years of tapping the trunk will assume a zig-zag configuration .


Effect of Palm Tapping on Trunk Development (Indian Method)

 

Yields of juice are, because of the reduced exposed surface area, much less than for the method described before, but the palms can be tapped every year, which can go on for an average of 25 years, though higher productive life spans have been recorded (32).

Together with some yield figures from literature  for the Wild date palm and the measured results from the earlier referred to tests between local and Indian tapping  some indicative figures on yields are given in Table.


Yields of palm sap (Indian and Local Method) 

Palm

Method of
tapping
L, local
I, India

Palm height
(grnd level
to terminal
bud, m)

No. of tapping
days
(x) dried up
(o) ongoing

Sap yields in l.

Yields in solids(kgs)

Solids (% age)

Averageyield/day (1)

Average solidyield/day (kgs)

Wild date palm
(Ph. sylvestris)

I

-

45 
(over a period
of 105 days)

75

7.5

10
(estimate)

1.7

0.170

Wild date palm
(high yielder)

I

-

45
(id)

13.5

13.5

10
(id)

3.0

0.300

Date Palm
(Ph. Dactylifera)

 

 

 

 

 

 

 

 

- Limsi

L

3.50

45 (o)

397.6

47.7

12.0

8.8

1.060

- Limsi

I

3.50

15 (o)

49.5

8.5

17.2

3.3

0.560

- Limsi

I

4.00

30 (o)

138.0

19.2

13.9

4.6

0.640

- Bikraari

L

5.80

41 (x)

400.1

44.7

11.1

9.8

1.090

- Bikraari

I

2.70

23 (o)

152.4

21.4

14.0

6.6

0.930

- Hallaawi

L

1.30

31 (x)

94.2

10.3

10.9

3.0

0.330

- Hallaawi

L

2.10

26 (x)

120.3

14.3

11.9

4.6

0.550

- Hallaawi

I

1.30

19 (o)

57.3

10.2

17.8

3.0

0.540

- Tabuuni

I

1.40

14 (o)

39.9

4.0

10.0

2.9

0.290

 

 

With due appreciation for the possible variations caused by varietal differences, height/age of the palms and length of the tapping period, certain tendencies can be discovered from these yield figures:

i. the yields of juice and solid matter by the Indian method on the date palm (Ph. Dactilyfera) are consistently higher than for the Wild date palm (Ph. Sylvestris).

ii. the daily and seasonal yields by the local method are higher than for the Indian method, but taking into consideration that by the local method the palm will not produce sap or dates for 2 years after tapping and in India the palms are tapped every year, the picture looks different. If indeed Ph. Dactilyfera could be tapped every year by the Indian method with the same result, most likely the total yield over three years would be higher than for the local method. This belief is reinforced by the fact that at least part of the crown leaves is left on and the palm's photosynthetic capacity is only partially impaired in contrast to the local method.

iii. in consequence of the lower daily yield but with the same if not more daily work required to harvest the palm sap for the Indian method, the labour hours involved per unit sap harvested is definitely higher.

With the production of sugar from palm sap as an alternative to the date crop in mind, the process of the different forms of sugar as practised in India as a cottage industry, will be briefly described. It is of vital importance to start work with a sound raw material, which involves a continuous fight against infection and multiplication of yeast. A freshly harvested sap will for the greater part consist of sucrose (say around 10%), minimal invert sugar, say less than 0.5% and small amounts of protein, gums, and minerals. To keep it in this form tools and pots should be kept clean, stagnant juice on the palm should be avoided and collected early in the morning. Time between collection and processing of the juice should be kept to a minimum. Artificial means to keep down the yeast are smoking the collecting pots by putting them head down on smouldering leaves before being used or by adding a small amount of quick lime to the pots. The latter method is definitely more effective to reduce the sugar inversion but for good quality gur (jaggery) production the lime has to be removed again by precipitation and filtering during processing.Four main sugar products are made from palm sap:

i. jaggery (gur), the crystallized whole (sometimes clarified) sap
ii. crystalline sugar with remaining molasses
iii. sugar-candy, large sugar cyrstals
iv. sugar syrup

In the most traditional method the juice is boiled down in earthenware pans filling in the holes of an arched clay oven (Fig. 99n). Fuel, e.g. palm leaves, is fed on one side of the stove and the smoke leaves from another hole or primitive chimney. The end point of boiling which may take a couple of hours is different for each of the intended products and usually recognized by the type of bubble which appears during boiling. In the case of jaggery making a separately prepared starter to accelerate crystallization is mixed in the boiling liquid just before pouring into a mould and left to cool and crystallize. Removed from the moulds jaggery presents itself as a light to dark brown crystallized block. The less invert sugar was present in the raw juice the better quality jaggery results. As an average the outturn of jaggery is 10-15% of the weight of the raw juice.

A typical composition of jaggery is:

Composition of jaggery

Moisture

8-10%

Total sugar

85-90%

Protein

<0.5%

Fat

<0.5%

Ca, Fe, P

Traces

Vitamin, B, C

Traces

Riboflavin

Traces

 

 

Strong promotional campaigns to encourage cottage industries in India have helped much to modernize jaggery making.

The use of lime is now common, which during processing is neutralized with phosphoric acid with PH indicator paper as a guide. The precipitated calcium phosphate is filtered off. In determining the end point of boiling also use is made of refractometers. Improved stoves have resulted in reduced fuel use and better controllable fires. Though remaining a cottage industry performed with simple means the qualitative aspects have greatly improved.

On the basis of the foregoing the question posed at the beginning of this Chapter (d) whether sugar from palm sap could become an alternative to a date crop, has become a little more but not fully answerable.

Physiologically it would seem that in sugar value the yield in the form of dates or in the form of sugar from sap are about equal, also in terms of the total productive lifespan of the palm (following the Indian method). Production-wise it would appear that it requires more labour hours and a longer annual involvement to produce one unit of sugar from sap than from dates. An economical evaluation therefore depends on the appreciation, organoleptically or monetary, attributed to the different products and the effect of their diversity and applicability. Each situation will have its own conditions and an on-the-spot feasibility is necessary. Technically however the date palm offers the possibility of alternative sugar production.

Pharmaceutical use:

Be it, that the date palm historically has been so closely interknit in the farmer's life and environment, or that the "Tree of Life" with its single head and trunk and division into male and female sexes with a corresponding reproductive system, was felt to resemble that of humans, the fact has transpired that the date palm has always had an aura of mystique around it, which at times devleoped into a palm cult. In Assyrian times, for instance, the palm was worshipped and depicted frequently in decorative art and for the embellishment has been witnessed in different times and places and, perhaps less pronounced, skill persists to date in the traditional date producing countries.

This esteem and adulation has probably also contributed to a sometimes overestimated belief in the medicinal powers of dates and other parts of the palm. There are many references to this effect in literature and if not for a desire of the search for alternative medicines, it is interesting (and sometimes amusing) to have a closer look at what benefit people obtained or thought to obtain from the different cures based on date palm products. In the foregoing text, in passing, mention has already been made of the depurative properties attributed to the terminal bud by Saharian palm growers or the use of pollen to enhance fertility in (ancient) Egypt. Medically, dates were recommended in mouth washes (an application most likely frowned upon by a present-day dentist); as a purgative or in gynaecologically related interventions . Dates formed part of various ointments, bandages and opthalmic prescriptions and Plinius reports: "dates are applied with quinces, wax and saffran to the stomach, bladder, belly and intestines. They heal bruises" .A notable Sheikh in the 16th Century elaborates: "dates fortify the body, enrich the blood, cure pains in the back, invigorate the loins whey they are atrophied and when boiled with milk they cut short fever and ague" .And from the same source: "the sap of leaves is a remedy for nervousness, kidney trouble and putrid wounds and calms the effervescence of the blood. Burnt seeds are made in an ointment for ulcers or a collyrium that produce long eyelashes". And this sampling of medicinal use of date palm products could not end without reference to the invigorating power bestowed on man when consuming male flowers and male spathe. Though the possible responsible agents to this effect have not been isolated scientifically, one wonders whether the chewing of spathe is practised for its flavour only.

Shade:

A chapter on the traditional uses of date palm products could not close without making mention (again) of an abstract but ever so real attribute of the date palm: giving shade and protection from wind, thus creating a micro-climate in which the harsh conditions of a hot and dry climate are tempered to make living conditions somewhat more sustainable. In the traditional date orchards especially in the oasis the density of palms is so great as to form an almost closed canopy.Extreme density and irregular stands of palms, however, diminish the opportunities for growing secondary crops and the introduction of mechanization in date palm cultivation.

 

source: http://www.fao.org/docrep/t0681e/t0681e11.htm

 

 

 


 

 

 

 

 

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