HASTENING THE COLORATION OF LEMONS 1 
By F. E. Denny 
Associate Chemist, Laboratory of Fruit and Vegetable Chemistry, Bureau of Chemistry, 
United States Department of Agriculture 
INTRODUCTION 
Lemons are picked not only according to color, but also according to 
size. Thus all fruits that have become yellow on the tree are picked, 
and in addition those with a green color if they have reached a certain 
size as determined by a wire ring carried by the picker. As a result, 
when lemons reach the packing house a proportion, which varies with 
the field and with the season, is green in color. Such fruits are sorted 
into light green and dark green grades, and the yellow color is subse¬ 
quently brought out by one of two general methods, the choice of method 
depending upon market conditions, that is, the time at which the house 
manager wishes to have the fruit ready for shipment. 
If a delay in shipment is desirable, the green lemons are placed in 
storerooms, usually in a basement, at a temperature of from 50° to 55 0 
F., with a humidity of about 80 per cent. The fruit becomes yellow 
in from 30 to 60 days. 
If, however, the demand for fruit is brisk, the ‘‘forced coloring’' 
method is used. This system has been much improved since its intro¬ 
duction many years ago. According to the original procedure, the 
fruit is placed in rooms or tents heated with kerosene stoves, with the 
result that the lemons turn yellow in one or two weeks. A source of 
humidity is often, although not always, provided to prevent shrinkage. 
It was thought that the coloration was brought about by the tempera¬ 
ture and humidity conditions in the heated rooms, but Sievers and 
True (17) 2 conclusively showed that the results were produced mainly 
by the gaseous combustion products from the kerosene stoves. Their 
experiments showed further that the gases did not lose their effective¬ 
ness by being conveyed from one room to another by pipes, using either 
forced or natural draft. Hence the more general method now in use 
consists in generating the kerosene-stove combustion products, hereafter 
referred to as “stove gas,” in a separate building, called a generator 
room, and carrying the gases through conduits to the various fruit 
rooms. 
Answers to a questionnaire sent to packing-house managers showed a 
general lack of agreement on most of the important details of operation. 
Uniformity in color and quality of fruit was not obtained, and it seemed 
impossible to fix upon any standardized procedure as being the one 
that gave the best results. This condition probably was due to the 
fact that no one knew what gas or gases in the sweat-room atmosphere 
caused the change. Since this seemed to be the critical question, experi¬ 
ments were started to determine if possible the identity of the gaseous 
constituent responsible for the coloration of the fruit. 
1 Received for publication, Jan. 23, 1924. 
* Reference is made by number (italic) to “ Literature cited,” p. 768-769. 
Journal of Research, 
Washington, D. C. 
(757) 
Vol. XXVII, No. 10 
Mar. 8, 1924 
Key No. E-28 
