220 TECHNICAL BULLETIN 15 



allowance being made for that present in the juice. The juice was then con- 

 centrated to a sheeting, spoon jelly test (104° to I05°C. or 219° to 221°F.). 

 The finishing point was checked by determining the weight of the pan 

 and contents from time to time. Inasmuch as jelly formation usually occurred 

 when the sugar concentration reached 67 to 69 per cent by weight, this fur- 

 nished a simple and accurate check upon the finishing point. The jelly was 

 weighed in the pan at once and poured through one thickness of medium 

 mesh cheesecloth into straight sided, 2-ounce jelly glasses. After skimming, 

 these were covered with melted paraffin and capped. Jelly strength, chem- 

 ical, and organoleptic determinations were made after 1 to 3 months storage 

 at 21° to 23° C. 



At first, jellies were made from all three extracts individually, together 

 with combinations of the first and second, as well as all three extracts com- 

 bined. Third extractions produced juice which seldom gave satisfactory 

 jellies unless acid was added. Moreover the pectin content was usually too 

 low to give a firm jelly. Naturally a jelly made from the third extract was 

 of poor color and flavor. Although combinations of all three extracts gave 

 fair to good jellies, it was decided that a combination of the first and second 

 corresponded more closely to home or factory practice and this was the pro- 

 cedure finally adopted. 



Chemical Methods 



Each sample of juice, i. e., first, second, and third extracts, was examined 

 for total titratable acidity, hydrogen ion concentration, soluble solids by 

 Abbe refractometer, Brix and specific gravity hydrometers, pectin by the 

 alcohol precipitate and centrifugal methods, pectic acid by the A. O. A. C. 

 (2) and centrifugal methods, sterility, and such physical characters as taste, 

 color, turbidity and sediment. Determinations of insoluble solids, soluble 

 solids, alcohol precipitate, pectic acid, total aciditj', pH value, and sterility 

 were also performed on the pulp. Determinations of total sugars, reducing 

 sugars and sucrose were made in some case?. The A. O. A. C. methods were 

 used wherever possible. 



The hydrogen ion concentration was determined in most cases colorimet- 

 rically, though several check determinations with the potentionmeter were 

 made. Notwithstanding the statement of Myers and Baker (8) that the 

 colorimetric method was of no value in the study of fruit juices, it was found 

 to l)e very useful and economical of time. Occasional checks by the electro- 

 metric method showed good agreement in pH values. 



In order to prepare samples for pectic acid, acidity, sugar determinations, 

 etc., from the pulp or fresh fruit, 300 grams of the well pulped and mixed 

 samples in a 2-liter beaker with 800* c. c. of water were boiled one hour, 

 the volume being kept constant by the addition of hot water at intervals. 

 The contents were transferred to a 2-liter flask, cooled, diluted to volume, 

 and filtered. 



It was found that, in drying the residue for the determination of total 

 solids, losses occurred where a temperature above 60° C. at 25 inches of 

 mercury in the vacuum oven was employed. This was due probably to 

 levulose decomposition. Similarly in drying alcoholic precipitate or pectic 

 acid it was found that decomposition occurred at 100° C, hence a tempera- 

 ture of 90 to 95 °C. was used. The absolute necessity of washing these 

 precipitates free from hydrochloric acid was also observed, as charring and 

 loss invariably occurred when this precaution was not fully carried out. 



