620 SCIENCE PROGRESS 



ence. As respiration must be the cause of this constant 

 heat production in the fruit, there must be a definite relation 

 between the respiration number and the temperature difference. 

 The temperature difference increases after a certain time of 

 storage, for instance, in apricots it is o«7° C. at the commence- 

 ment of storage, while after four to five weeks it is i° C. Thus 

 a very simple and convenient means might be found for indicat- 

 ing when the time has arrived to remove the fruit from the 

 store, as experiment would show at what temperature differ- 

 ence it becomes inadvisable to keep fruit longer. 



It is easy to understand that it would be possible to keep 

 the temperature in the cold store for fruit below zero, partly 

 on account of this temperature difference, and partly because 

 the freezing point of the fruit lies a little below o° C, namely 

 between — i° and — 2° C. It has indeed been the tendency 

 in the history of the cold storage of fruit to use lower and 

 lower temperatures. The first temperatures used were 8° to 

 io° C, later it was found that fruits kept longer if kept at 

 from 4 to 5° C, while now temperatures about zero are very 

 generally used, but it is scarcely generally realised that it 

 is possible to go still lower without any danger of freezing the 

 fruit. 



Thus there is not much scope for varying the conditions 

 in the cooling chamber as regards temperature. The other 

 factors which allow of variation are humidity, light, and 

 movement of air, but in respect to these, conditions have to 

 be worked out independently for each species, or even variety. 

 Generally speaking, for soft fruits, which are easily destroyed 

 by fungi, it is preferable to have a moderately dry atmosphere 

 which is kept in motion, while for stone fruit and apples which 

 shrink owing to loss of water, it is preferable to have moist 

 and still air. In regard to illumination a diversity of opinion 

 exists, some writers urging complete darkness and others a 

 high light intensity. 



As the value of some fruits depends on specific aroma due 

 to the presence of volatile acids or alcohols, cold storage may 

 be of no commercial value in these cases unless special precau- 

 tions are taken to prevent evaporation such as by wrapping 

 the fruit in paper or dipping it in a liquid which easily 

 solidifies and covers it with a protective glaze. 



(To be continued) 



