138 Bulletin 135, Utilization of Cull Citrus Fruits

each square foot of heating surface could be evaporated in an
hour, approximately 85 percent of the weight of the juice being
removed. The required heat was obtained from steam at less
than one pound pressure. However, the juice concentrated in
this copper pan had a very undesirable metallic taste and dark
color, and the remaining tests were made in a special solid
aluminum pan, also heated with steam.
 An important point brought out by this work was the ne-
cessity of keeping the temperature as low as possible in order
to avoid injury to the taste. It was found that, altho 50C. was
not high enough to cause injury, it was difficult to avoid over-
heating around the outside layers of the concentrated mass, and
hence an indicated temperature of 40 to 50C. was much safer.
For this same reason it is better to concentrate to only about
20 percent of the original volume, altho it is possible, with care,
to evaporate to 15 percent.
 The presence of suspended matter in both orange and grape-
fruit juice constitutes a chief difficulty in all concentration
work, and the more thoroly the juice is clarified the more read-
ily is it concentrated. In the case of grapefruit juice, however,
there is normally a smaller amount of suspended solids than in
orange juice, and it is therefore practicable to concentrate
grapefruit juice to as low as 12 percent of its original volume.
 It was found that the concentrated juices were subject to
the same discoloration as the fresh ones, but that it could be
prevented by the same method, viz., sealing in absence of oxy-
gen. It has been found by other investigators that concentrated
lemon juice will keep without pasteurization, on account of its
high acidity. One might expect that this would also be the
case with orange and grapefruit juices. Mr. McDermott's ex-
periments along this line were not extended enough to be con-
clusive but they indicated the probability that concentrated
orange juice cannot be relied upon to keep without pasteuriza-
tion; grapefruit juice, on the other hand, will very probably
keep under these circumstances, even when diluted with a small
amount, one-fourth, or less, of orange juice.
 One disadvantage of the concentrated juice is that it is
necessary to add flavoring after concentration, as the vacuum
process removes nearly all flavoring materials from the juice.
 (C) THE PREPARATION OF DRY JUICE
 Considerable work was done along the line of preparing a
dry product from orange and grapefruit juice. It was found to