222 



Bulletin 230. 



cannot distinguish between tubers of good quality and those of 

 poor quahty when they are mixed in bulk. It is therefore very 

 desirable that some physical feature or aspect be found which will 

 enable one to recognize potatoes of good quality upon superficial 

 examination. The degrees of quality in the table on page 223 is 

 expressed numerically upon an estimate of all of these factors, and 

 also upon the mealiness or sogginess of the tuber when boiled in 

 water. 



What Causes Mealiness? 



In cooking, mealiness is the most important consideration in 



estimating quality. In 

 general, mealiness fol- 

 lows upon the presence 

 of sufficient starch in 

 the cell to rupture its 

 walls when boiled in 

 water. The grains of 

 potato starch expand 

 and coalesce when 

 boiled in water (Fig. 

 175), and if the cells are 

 sufficiently full of these 

 bodies (Fig. 176) the 

 boiling will cause the 



cellular structure to be 

 Fig. 177. — From the internal medullary area shoiving Uy(~.]rar, Inwn nn 1 



the paucity of starch in the cells of this part. 



degree oi mealmess is 



the result. When the requisite amount of starch is not present 



in the cells (Fig. 177), its walls are not broken down in 



cooking, hence the tuber retains its form, or is soggy. When 



the '.internal medullary area is large and branching (in the 



variety Doe's Pride) the external medullary area is not uniform, 



and when the tuber is boiled in water it is hard and soggy 



or it contains portions which will not mash uniformly and readily. 



That there is a marked difference between the starch content of 



these two portions is shown by chemical analyses, by microscopical 



examination and by the specific gravity. Coudon and Bussard 



(Ref. cited p. 220) found upon chemical analysis of five varieties, 



the following percentage of starch, protein and water in the different 



portions : 



