|Comparative Study of Solar and Sun Drying of Fish in Ecuator (NRI)|
Comparison of the five drying methods investigated can be based on four criteria:
1 Drying rates
2 Final moisture content
3 Product quality
There was very little difference in overall drying times between
the three solar dryers, and similarly very little difference between rack drying
and drying on the rocks. However, fish dried in the solar dryers took an average
of about 60 - 65% of the time required for sun drying to achieve a final
moisture content of 20%. Under fine and sunny conditions, fish such as lisa or
pampano would be expected to dry in about 3 days in a solar dryer, compared with
5 days when dried in the sun. Drying times of 4 and 6 days respectively would be
expected with cloudy weather. It should be remembered that these times are only
strictly applicable to conditions appertaining to the Galapagos at a certain
time of the year and are only indicative of performance elsewhere.
As the initial drying rates for sun and solar drying were similar, and as a reasonably clean product was obtained by drying on the rack, it may be worthwhile considering sun drying on a rack initially and then completing drying in a solar dryer, thus increasing the throughput of the solar dryers.
Final moisture content
The reduction in moisture content possible by drying in a solar dryer (to 13%, on average) was consistently greater than that obtained by sun drying (21%, on average). As explained previously, storage life is dependent in part upon the moisture content and, therefore, solar drying could give a product with a much longer storage life than sun drying. The yield, however, would be slightly less.
It was considered that the fish dried in the three solar dryers were, almost without exception, of very high quality. However, for the fish dried in the cabinet dryer, a possible health hazard might exist because of the relatively large numbers of flies which were attracted into the cabinet. Rack-dried fish were judged to be of higher quality than those dried on the rocks, which in turn were better than those dried by the local fishermen.
The solar dryers each had a capacity of about 8 kg of prepared fish and the rate of production of dried salted fish was approximately 1.25 kg m-2 day-1 . The rate of production by sun drying was 0.75 kg m-2 day-1 for the. same 8 kg capacity. The cost of materials for the tent dryer (2,093 sucres) as built was slightly less than that for the SCD dryer (2,252 sucres) and considerably less than that for the cabinet
dryer (3,110 sucres), using prices currently* applicable in the Galapagos. All three solar dryers were more expensive than the rack (653 sucres) and there were no material costs for the lava rocks. Due to the proportionally lower cost of plastic sheet, which would form the major factor in maintenance costs, the cabinet dryer would be much the cheapest of the solar dryers to operate.
The principles of construction and operation of the tent dryer would be easier to communicate to an artisanal fisherman than those for the SCD and cabinet dryers. In addition, construction time for the tent dryer (6 man-hours) is very low in comparison with that for the SCD and cabinet dryers (15 and 25 man-hours respectively).
In conclusion, it can be said that rack drying gave a better product than drying on the rocks and all the solar dryers gave a better product and at a higher rate than did the sun-drying methods. The cabinet dryer has a major problem with flies which could be a serious health hazard. Even though both dryers performed equally well, on grounds of cost and ease of construction, the tent dryer appears more suitable than the SCD dryer for the individual fisherman. In the Galapagos Islands, the capacity of these solar dryers would be sufficient to dry part of the individual fisherman's daily catch. However, a greater capacity would be required for the larger boats, several of which often return to port together after 15 - 20 days' fishing.