515 



The fact, established by Einliolf and Goppert, that potatoes freeze with 

 greater degrees of cold without becoming sweet and that those which have 

 become sweet remain soft, is explained simply by Miiller-Thurgau's^ experi- 

 ments. He found that the potato tuber freezes only at 3 degrees C. below 

 zero. To be sure, its real freezing point lies possibly about i degree below 

 zero, but the cell juices must first be cooled down to 2 to 3 degrees below 

 freezing, i. e., be "supercooled," before the first ice crystals can be formed 

 between the cells. Naturally, a lowering of the temperature from zero to 2 

 degrees below zero retards many life processes. Among these are two which 

 come especially under consideration here; viz., the transversion of the starch 

 into sugar and the utilization of the sugar. It may be assumed that the 

 sugar from the protoplasm of the cell is partly used in respiration, partly 

 during the period of growth in the regeneration of the cytoplasm and the 

 starch reversion. Miiller-Thurgau^ found, in fact, that potatoes which had 

 become sweet after having been kept at a temperature of 20 to 30 degree C. 

 had increased their starch content at the expense of the sugar. This had 

 disappeared ; with a lowering of the temperature to o degrees and 2 degrees 

 below zero, the process of respiration (and most probably also that of the 

 regeneration of the protoplasm) decreases, while the transversion of the 

 starch into sugar does not fall off so quickly. Consequently, the sugar 

 accumulates in the tuber and becomes noticeable in the flavor. It amounts 

 to about 2.5 per cent, of the fresh substance, yet comparatively wide fluctu- 

 ations are found in different individuals of the same variety. A higher 

 water content in the tubers favors the turning sweet. This increase of sugar 

 corresponds to the loss of starch yet, according to Czubata's'' analyses, no 

 corresponding proportion can be proved in the two processes. According to 

 Czubata, a part of the protein passes over from the insoluble into the soluble 

 condition during freezing. Miiller assumes that the ferment here concerned 

 increases with the lower temperature. 



If potatoes which have become sweet are left for some days in a room 

 with a temperature of more than 10 degrees, respiration increases and the 

 sugar is oxidized, i. e., the potatoes lose their sweetness and in this way 

 again become usable for cooking. Other proposed means, as. for example, 

 the leaching of the tubers with water, did not lead to any results. Besides 

 this, however, it should be emphasized that one need not hesitate to use 

 potatoes for seed which have become sweet. Such potatoes freeze only 

 with a greater degree of cold than non-sweet tubers^. 



I should like to add here supplementarily a statement made to me 

 verbally that in Reinerz a cellar is said to exist in a cave in which potatoes 

 become sweet even without the action of frost. This phenomenon is 



1 Miiller-Thurgau, Ein Beitrag zur Kenntnis ties Stoffwechsels in stiirkehal- 

 tigen Pflanzenorganen. Botanisches Centralbl. 1882, No. 6. 



2 Landwirtsch. Jahrb. 1883, p. 807. 



" Czubata, Die chemischen Veranderungen der Kartoffee beim Frieren und 

 Faulen. Oster.-Ungar. Brennerei-Zeitung 1879; cit. in Biedermanns Centralbl. 

 1880, I, p. 472. 



■1 Muller-Thurgau, Landwirtsch. Jahrb. 1883, p. 826. 



