NO. 2(l92l) REMARKS ON CANNING 57 



either in a special oven or in the (Beypore) ' solar oven,' * in which 

 a temperature of over 300" F. can be obtained during the hot 

 weather and always, on sunny days, above 250° F. It is well 

 known that baking thoroughly hardens the lacquer, and that, 

 within limits, the higher the temperature of baking the better the 

 lacquer will stand subsequent heat, as in processing at 240° F., 

 without alteration. This double lacquering is a great improvement, 

 and when vegetable parchment paper is added as a protection, 

 even prawns keep very fairly for years, being frequently as bright 

 as when packed. But this lacquering is not quite sufficient per se 

 and other linings are needed and in some cases adopted ; a cheap 

 ' enamel ', unaffected by steam at 250° F., is now hoped for at 

 Beypore, and this will prevent all further difficulty; cans will then, 

 be wholly ' sanitary '. 



* The iolar oven is a shallow teak box, the top of which is a double sash of glass; 

 the box is blackened inside with a dead black and insulated by insertion in a larger box 

 with saw dust or rice-husk insulation. The whole is then so mounted that it can be kept 

 facing the sun at such angle that the rays will always be perpendicular to the glass sash. 

 Since direct rays will penetrate glass readily but radiated rays with difficulty, the heat is 

 trapped within the box and produces a temperature usually doul^le or more than double 

 the external sun temperature as measured by a thermometer placed in the open sun. 

 With wings of tin plate set at an angle with the glass surface, the temperature has been 

 raised to 325^ F. in March. Since soft solder softens at not much above 300° F. this heat 

 is more than sufficient. Baking in this oven costs practically nothing. 



