6o6 SCIENCE PROGRESS 



in the former case the leaves remain tough and leathery, 

 whereas in the latter they are quite softened and fit for eating. 

 Slow methods of cooking are thus unsuitable for obtaining the 

 best results with vegetables. 



There are three methods in common use for cooking green 

 vegetables : (i) by throwing into excess of fast boiling water ; 

 (2) by steaming over boiling water * ; and (3) by boiling in a 

 very small amount of water, so that no straining is necessary 

 before serving, the vegetables being mainly cooked in their 

 "own juices." The last is the so-called " conservative method." 

 In order to preserve the green colour of cabbage and similar 

 vegetables it is a common practice to add a little bicarbonate 

 of soda to the cooking water : this also considerably hastens 

 the softening of the tissues. 



The relative merits of these methods must now be considered 

 in relation to our knowledge of the properties of vitamines. 



In experiments made by Harden and Zilva ' with fresh 

 orange-juice, it was found that, after being made just alkaline, 

 the juice quickly lost its anti-scorbutic efficacy. In the case 

 of vegetables, therefore, there is every reason to believe that 

 this destruction would be still more rapid when sodium bicar- 

 bonate is added to the cooking water, which is kept at or near 

 boiling-point. 



According to Masters and Garbutt ' soda or sodium bicar- 

 bonate is commonly added to cooking water for two reasons), 

 viz, to " soften " the water and to preserve the bright green 

 colour of the vegetables. These authors point out that nothing 

 is gained by " softening " the water, since green vegetables 

 discolour as readily when cooked in soft as in hard water. 

 The discoloration appears to be due to the formation of some 

 acid substance during cooking ; this may be prevented by the 

 addition of a volatile alkaline salt such as ammonium car- 

 bonate, in small quantity. According to these authors, 

 addition of about | gm. ammonium carbonate to a litre of water 

 would reduce the time needed to steam cabbage from an hour 

 (steamed over plain water) to 18 minutes (steamed over 

 water to which the carbonate has been added). In the case of 

 the conservative method, addition of tV gm- carbonate reduced 

 the time of cooking from i hour to 12 minutes, and left " no 

 appreciable smell of ammonia." In the light of the experi- 

 ments of Harden and Zilva, already quoted, however, it seems 



* In reckoning time for steaming, allowance must be made for loss of heat 

 involved in opening the steamer and introducing a cold substance. In the 

 experiments quoted on p. 605 small amounts were introduced and the ther- 

 mometer registered the desired temperature within two or three minutes of 

 replacing the lid. In domestic operations this is often not possible, and the 

 time for cooking must be reckoned from the time when the steam chamber is 

 again full of steam at or near 100° C. 



