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THE MONTHLY BULLETIN. 



CALIFORNIA STATE COMMISSION OF HORTICULTURE 



Vol. VI. August, 1917. No. 8 



STANDARDS OF MATURITY FOR THE WASHINGTON 

 NAVEL ORANGE. 



By E. M. Chace, Chemist in Charge, Citrus By-Products Laboratory, U. S. Depart- 

 ment of Agriculture, Los Angeles, Cal. 



Since the publication of the standard of maturity for Washington navel oranges 

 by the Bureau of Chemistry in 1915, much interesting comment upon it has beeu 

 made both by individuals and the press. This standard, popularly known as the S to 1 

 test, was first made public in the fall of 1914 as a tentative standard and was finally 

 adopted after another year's investigations. 



The standard depends upon the ratio between the soluble solids and the citric acid 

 contained in the juice of the orange. The soluble solids of the orange consist of from 

 65 per cent to JO per cent sugar, the remainder being chiefly citric acid, soluble 

 forms of nitrogen, pectin, and other non-sugar material. 



During the first season after the test had been published and given to the Cali- 

 fornia growers, many interesting phenomena were discovered by various operators 

 who were constantly testing fruit thrbughout the citrus regions. It soon became 

 apparent that very green fruit would in many cases pass the test, owing to the fact 

 that the acid had not yet reached the maximum. In the growth of an orange, there 

 is a period when the ratio between sugar and acid is comparatively high, and as the 

 fruit matures, the acid increases together with the sugar until the former reaches 

 its maximum, after which it will decrease while the sugar continues to increase. This 

 often results in an abnormally high ratio for a short period, followed by a normal 

 and lower ratio, before the final ripening period sets in. An illustration typical of 

 these cases was found in a Nordhoff grove. On December 26, the fruit from the 

 selected tree in this grove contained juice having 11.8 per cent soluble solids and 1.63 

 per cent acid, giving a ratio of 7.2. On January 2 the solids had risen to 12.3 per 

 cent and the acid to 1.75 per cent, giving a ratio of 7.0. On January 9 the figures 

 were 12.4 percent solids and 1.77 per cenl acid, the ratio still being 7.0. On January 16 

 the solids were 12.2 per cent, the acids 1.81 per cent, with a ratio of 6.7 One week 

 later, on January 23, the solids were 12.7 per cent, the acids 1.43 per cent, with a 

 ratio of 8.9. On February 1 the solids were 12.5 per cent, the aeid 1.46 per cent, 

 the ratio being 8.6. On February 16 the solids were 12.6 per cent, the acid 1.57 per 

 cent, the ratio being s.O. On February 23 the solids were 12.S per cent, the acid 

 being 1.38 per cent, with a ratio of 9.3. After that date, with one exception, the 

 solids-acid steadily increased. 



While it had been recognized during the first season that some very green fruit 

 would pass the standard, it had not been thought that such fruit would be given 

 commercial consideration. There has. unfortunately, been some attempt, however, 

 to take advantage of this fact and to ship fruit even before it had begun to approach 

 the final sta^o of maturity, and the Protective Association in Tulare County, in 

 order to meet this condition, adopted ;i color standard which prohibited the sweating 

 of fruit before it had reached a color in excess of 50 per cent. 



It was also discovered that unless the juice was thoroughly extracted from the 

 pulp of the orange, that the correct solids-acid ratio could nol he determined. 

 Oranges which are very lightly squeezed have a lower solids-acid ratio than those 

 which are thoroughly pressed. This is due in a large part to the fact that the pulp 

 nearest I he center of the fruit, which is first removed by the usual method of 

 Bqueezing contains more acid and less sugar than that near the rind. 



Another phenomenon was brought out in the fact that oranges, the juice of which 

 contained a high percentage of soluble solids, and were therefore high in sugar, wet-.' 

 found to taste aweeter than those containing a low percentage, even when tin- ratio 

 of acid in the sweeter orange was higher than that in the poorer. This lias led to 



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