When speaking of food losses, a first consideration is the distinction between perishable and non-perishable or preservable foodstuffs (see the comparative table in an annex, listing foodstuffs according to their suitability for storage: FAO, 1984). In one of its studies assessing losses of perishable products through handling or post-harvest operations, the special FAO loss-prevention programme presents the following conclusions: if harvest operations, placing in storage (stacking and/or packaging in warehouse), storage and transport are defective, losses separate out as follows:
|
harvesting: |
5-8% |
|
placing in storage: |
15-20% |
|
storage: |
5-10% |
|
transport: |
10-12% |
|
i.e. a theoretical total of: |
35-50% |
Although average losses are not in fact so high when an overall calculation is made, they are still far from negligible. While the situation is certainly better for non-perishable products, it is still unsatisfactory and could be improved. This can be seen, for example, from an Asian study on the post-harvest chain for grains (cereals), which analyses losses from the main operations and estimates percentages for those that could be avoided. Its conclusions are as follows: each year 5% of the losses from poor monitoring and regulation of humidity, and another 5% of the losses from problems connected with handling, storage and processing, could be avoided (study by P. Douglas, G. Dubrick and G. Sullivan, ASEAN).
In this connection, we would note that in industrialized countries, grain producers accept a 1% wastage during combine-harvesting and a 2% wastage during storage as normal, making 3% for these two operations alone. The current rule is stricter, estimating that an acceptable loss rate would be 0.75 to 1% after 9 to 10 months' storage. The loss rate accepted in the commercial sector is usually 0.75%.
An Argentinean study has calculated the financial effect of post-harvest losses on commercial management costs:
Effect of losses on commercial management costs (source: C.E. Fru, Cor, Argentina, 1993)
|
percentage loss |
Kg of foodstuff marketed |
Cost/kg in $US |
percentage rise in cost |
|
0 |
1.047 |
0.65 |
0 |
|
5 |
0.995 |
0.68 |
5 |
|
10 |
0.942 |
0.72 |
11 |
|
15 |
0.890 |
0.76 |
17 |
|
20 |
0.838 |
0.81 |
25 |
Like loss assessment, calculation or assessment of costs and cost prices entails considerable difficulties, if not uncertainties, if all the relevant factors are to be taken into account. It is particularly important to be clear as to whether the "rational" economy of an industrialized country or that of a developing country is involved. Even then, such figures are always of relative value and are dependent on a socio-economic framework that must never be forgotten. These difficulties are certainly one of the main reasons why economic data are poorly developed in works on post-harvest systems and losses.
The costs (in monetary terms or as a percentage) given in the following tables come from widely varying sources and concern three essential operations in the post-harvest pipeline for cereals: threshing, drying and storage. First is a study of a rice project in Mali (the Harpon Project) which compares the costs of traditional hand threshing and mechanized threshing with a ventilator, noting the corresponding losses:
|
|
cost of threshing |
loss of grain |
|
traditional threshing |
12% |
5-10% (at least 6 months after harvesting) |
|
mechanized threshing |
8% |
1-2% |
|
current threshing (Votex threshers) |
4.5% |
1-2% |
The new threshing techniques thus reduce both costs and losses markedly, apart from the saving in time and toil.
The NRI manual financed by FAO (Rome, 1994, unpublished) contains a detailed table on paddy drying, giving the technical specifications of the drier and the different unit costs of three methods of reducing the moisture content of freshly cut paddy from 20 to 14%. Some relevant data are extracted from the table, and the case of drying a small amount is also given for each variant:
|
|
batch-in-bin |
recirculating batch |
continuous-flow |
|
Capacity of dryer (tonnes) |
2 |
5 |
5-10 |
|
Drying performance in tonnes/day |
6 |
15 |
60 |
|
Investment, drying equipment only ($US) |
800 |
15000 |
40000 |
|
Total annual cost |
960 |
6300 |
19200 |
|
Cost per tonne ($US) |
4 |
10.5 |
8 |
We would merely highlight the differences in unit cost per tonne, which show that drying a small amount turns out to be the most economical system, and that continuous-flow drying is cheaper than recirculating a batch. The full table is given in an annex and confirms this conclusion, since for a large amount the most economical system is continuous-flow, followed by the first system (batch-in-bin) and lastly the recirculation system.
Studies on the economics and management of the cereal post-harvest system in France indicate that storage costs come to 12% of the value of the grain. The cost calculations in the summary report on the Accra Workshop cited above have the advantage of comparing the cost/benefit ratio for three different granaries after six months' storage. As before, these figures refer to trials on maize storage in Benin, i.e. a small-scale, village environment, and compare the performance of a number of improved granaries with that of a control granary of the traditional type. The maize was stored in cobs still in their husks, and the two improved granaries, BT 2 and BT 3, had capacities of 2 and 6 tonnes respectively. The document specifies that "the cost of storage comprises costs of construction, phytosanitary treatment and handling into storage", and that "the cost/benefit ratio is the greatest value achieved in differentiating the sales of maize":
Costs of storing maize cobs in husk in improved and traditional granaries
|
Type of granary |
Storage cost |
Cost/benefit after 6 months |
|
BT 2 |
4.300 CFAF/t |
2.125 CFAF/t |
|
BT 3 |
3.150 CFAF/t |
2.600 CFAF/t |
|
Control, traditional |
4.100 CFAF/t |
2.600 CFAF/t |
It can be seen that technical improvements in granaries make storage a profitable operation (see annex for the results of these comparative trials).
1st Table of G. YACIUK
|
Region |
Losses in % |
Remarks and sources of information |
|
Rice West Africa |
6-24 |
Drying 1-2; On-farm storage 2-10; Parboiling 1-2; Milling 2-10 |
|
Sierra Leone |
10 |
(NAS, 1978) |
|
Maize Benin |
8-9 |
Traditional on-farm storage 6 months improved silo storage (NAS, 1978) |
|
Ghana |
7-14 |
(NAS, 1978) |
|
Ivory Coast |
5-10 |
12 months stored on the cob (NAS, 1978) |
|
Nigeria |
1-5 |
On-farm storage (NAS, 1978) |
|
5.5-7 |
6 months on-farm storage (NAS, 1978) |
|
|
Togo |
5-10 |
6 months central storage (NAS, 1978) |
|
Millet Mali |
2-4 |
On-farm stores (Guggenheim, personal comments) |
|
10-14 |
Central stores (Guggenheim, personal comments) |
|
|
Nigeria |
0.1-0.2 |
On-farm stores (NAS, 1978) |
|
Senegal |
see Table 1 |
(Yaciuk, 1976) |
|
Sorghum Nigeria |
0-37 |
On-farm stores (NAS, 1978) |
|
Senegal |
see Table 1 |
(Yaciuk, 1976) |
Source: Yaciuk and Forrest - 1979
Table taken from "TRAINING MANUAL ON GRAINS" - Dryer specifications, estimated performance, and cost for drying freshly harvested field paddy (raw paddy) from 20% to 14% moisture.
|
|
Batch-in-bin |
Recirculating batch |
Continuous-flow |
|||
|
small |
large |
small |
large |
small |
large |
|
|
Dryer specifications |
||||||
|
Capacity (tonne) |
2 |
100 |
5 |
10 |
5-10 |
10-25 |
|
Approximate Power consumptionhp |
3 |
10 |
15 |
25 |
15-20 |
25-50 |
|
Approximate Air Flow (m/s per tonne) |
50 |
23 |
56-85 |
70-100 |
85-115 |
115-140 |
|
Approximate Drying Air Temperature (°C) |
43 |
43 |
60-80 |
60-80 |
60-80 |
60-80 |
|
Approximate Burner Capacityn (kW) |
30 |
1,200 |
600 |
1,200 |
1,200 |
2,400 |
|
Estimated performance |
||||||
|
Drying Capacity (t day) from 20% to 15% moisture |
6 |
10 |
15 |
30 |
60 |
100 |
|
Annual Drying capacity (tonnes) (40 days/year operation) |
240 |
400 |
600 |
1200 |
2400 |
4100 |
|
Estimated Costa (US$) |
||||||
|
Investment, Drying equipment only |
800 |
6000 |
15000 |
24000 |
40000 |
50000 |
|
Annual Fixed cost |
240 |
1800 |
4500 |
7200 |
12000 |
15000 |
|
Annual Variable cost |
720 |
1200 |
1800 |
3600 |
7200 |
12000 |
|
Annual Total cost |
960 |
3000 |
6300 |
10800 |
19200 |
27000 |
|
Cost tonne |
4.0 |
7.50 |
10.50 |
9.0 |
8.0 |
6.75 |
First tables the "Synthesis..." Accra Technical Days - FAO
The evaluation of the damage caused by insects (Table 5.3) shows the significant effect of the photosanitary treatment linked to the preparation of cobs before storage carried out in improved stores. There has been less than 1,5% weight loss after 6 months in an improved store than 6,2% loss in a traditional store.
Evolution of grains water content
|
Store diameter |
During harvest |
After 3 months storage |
After 6 months storage |
|
2 m |
19,7% |
15,3% |
12,6% |
|
3 m |
20% |
15,8% |
13,6% |
|
4 m |
20,7% |
16,7% |
15,4% |
|
Witness |
18,9% |
15% |
11,7% |
Damage due to mould (% of mould grain)
|
Store diameter |
During Harvest |
After 3 months storage |
After 6 months storage |
|
2 m |
2,3% |
2,9% |
3,4% |
|
3 m |
3,4% |
5,7% |
5,1% |
|
4 m |
4,2% |
11,4% |
10,7% |
|
Traditional store |
2,9% |
3,0% |
3,2% |
2 tables illustrating the "Synthesis...", technical days of ACCRA - FAO % of weight loss due to insects
|
Store diameter |
During harvest |
After 3 months storage |
After 6 months storage |
|
2 m |
0,4% |
0,7% |
1,3% |
|
3 m |
0,2 % |
0,6 % |
0,9% |
|
4 m |
0,9 % |
0,9 % |
1,3% |
|
Traditional store |
0,6 % |
1,6% |
6,2% |
(Source: Afomasse, 1994)
Socio-economic results
The cost of storage includes building, phytosanitary treatment and storage costs. The ratio cost/benefit is the added value withdrawn when selling of maize is differed.
Storage cost
|
Type of storage |
Storage cost |
Cost/Benefit after 6 months |
|
BT2 |
4.300 F.CFA |
2,125 F/tons |
|
BT3 |
3.150 F.CFA |
2,600 F/tons |
|
Traditional |
4.100 F.CFA |
|
Losses caused by parasites are slightly reduced with the use of a good storage structure associated to a timely harvest, a preparation of the cobs before storage and a phytosanitary treatment. The auto-extension of building construction of improved stores started developing in the project area, which shows the importance of the technique. The farmers trained by the project now offer their services against payment to other farmers.
