428 EVENING DISCOURSES 
over a period of 3 hours produces a good, pale colour with haddocks. If the 
deeper colour of the Finnan cure is required, the temperature should be 
maintained at about 80° F. for a further 2 hours. During the process the 
fish naturally loses water, and it is clear that the final result must depend on 
the rate at which the water is lost—i.e. it will depend on the humidity and 
the rate of displacement of the air. Experiments have shown that increase 
in the velocity of the air beyond ro ft. a second has little effect, but up to 
that speed the loss of water by the fish increases with the air-speed, provided, 
of course, that the air is not already saturated with moisture. ‘That brings 
me to the third variable, humidity. The important point here is the 
capacity of the air to take up water. In practice it is found that, for a rise 
in temperature from 70° to 90° F., a relative humidity of about 50 per cent. 
gives the best results, producing a satisfactory cure, and at the same time 
keeping the loss of Weight down to the minimum, namely, about 25 per cent. 
for the fully cured fish. 
Knowing the best conditions, controls of temperature, humidity and 
movement of the air are very easy problems for the physicist, and the 
summed result is complete control of the drying of the fish. Control of 
the smoke, which is responsible for the antiseptic substances, has been 
achieved by separating the two processes of drying and smoking. ‘The 
drying kiln is heated by controllable methods such as gas-burners or 
electrical heaters, and the smoke is made in a box external to the kiln. 
Burning sawdust is used, and the rate of burning is governed by a small 
electric blower, the smoke being piped to the kiln through a conditioning 
tank in which its temperature is lowered to about 60° F. At this tempera- 
ture the smoke is fully saturated with moisture, but as the kiln is at a higher 
temperature, the percentage humidity drops to the required degree on 
entering the kiln. ‘To produce the even smoking of the fish, the experi- 
mental kiln at Torry was fitted with fans to ensure even circulation of the 
smoke, first in one direction and then in the opposite. With such an 
experimental plant it was a simple matter to produce any desired cure with 
certainty ; no matter what the external atmospheric conditions might be, 
it was easy to secure the evenness of cure, brilliance of colour, cleanliness, 
and excellence of flavour on which the quality of the finished product 
depends. Moreover, ‘ droppers’ were avoided, ‘droppers’ being the 
softened fish which fall off the hooks. 
It may be thought that the expense of such a plant would render it 
uncommercial, but I believe this is not the case. ‘The improvement and 
consistency in the product, and economies in other ways, are considerable, 
and I am glad to say that commercial kilns are being developed with success 
on these lines. 
Salting —Another old process of preservation is salting, and it is of special 
importance to the herring fishing industry, for about one-half of the catch is 
treated by this process. 
The common salting process is the ‘ hard’ cure in which the finished 
product contains about 15 per cent. by weight of salt, as against 0-2-0°3 
per cent. in the fresh fish. It is essential to keep the concentration of 
salt high if the fish is to be kept in good condition for a reasonable period 
of time at normal temperatures. Unfortunately, the export trade in the 
‘ hard ’-cured fish has seriously diminished, and at home the ‘ hard ’-cured 
fish makes no strong appeal to the consumer’s palate, being both too salt 
and too desiccated. In 1932, the last year for which figures are available, 
the export trade was only some 4 million hundredweights, as against over 
64 millions in 1913. With these facts in mind, research has been 
carried out with the object of relating palatability and keeping quality with 
