1156 
Journal of Agricultural Research 
Vol. XXX, No. 12 
moved by prolonged washing with 
water. The calculation of the non-tan¬ 
nin astringency to grams per 1,000 c. c. 
by the use of the factor used for tan¬ 
nin, involves a large error, as the sub¬ 
stances making up the astringent non¬ 
tannins are highly diverse in character. 
It has been known since the work of 
Neubauer (50) in 1872 that the pig¬ 
ment of a certain red wine, studied by 
him, when prepared in a fairly pure 
state, had only 30 per cent the reduc¬ 
ing power of pure tannin (0.00754 
gram of Neubauer’s preparation 
equalled 0.002296 gram tannin in 
reducing power for KMn0 4 ), while 
Kelhofer (39) found that when he 
titrated purified pear tannin with 
KMnO ( the results indicated only 
64 per cent of the weight of tannin 
actually employed in the determina¬ 
tions. For these reasons the results 
obtained when the method is employed 
for a large number of juices which vary 
considerably in nature and amount of 
coloring matter and other oxidizable 
nontannins present are at best only 
roughly comparative. 
A study of the literature on methods 
of determination of tannin in fruit 
juices was undertaken in the hope that 
a method could be found which would 
differentiate somewhat more accurately 
between tannins and nontannins and 
which could be used in work with 
fresh juices under rather primitive 
field conditions. A review of the 
summaries by Nierenstein (51, 52) 
and Czapek (18), and of the work of 
Spiers (66), Laborde (41), Fresenius, 
and Griinhut (22), Meyer (47), and 
others indicated that there is no 
method which can be depended upon 
for quantitative results which can be 
used in field work. Since the results 
reported in the literature are expressed 
in terms of the Loewenthal-Schroeder 
method as modified by Proctor, its 
employment would permit direct com¬ 
parison of results and it was therefore 
employed for the field work. Another 
consideration which led to the aban¬ 
donment of any attempt to obtain 
anything more than roughly compara¬ 
tive results upon the fresh juices is the 
very large and rapid change in soluble 
astringent constituents which freshly 
pressed juices undergo upon exposure 
to the air. As a consequence of this 
alteration, which has been recorded by 
Lindet (43), Hotter (32, S3), and 
studied especially by Kelhofer (35, 36, 
37, 39), the tannin content of a freshly 
pressed fruit juice is a maximum which 
decreases as the juice passes through the 
processes of bottling and pasteuriza¬ 
tion to reach a stationary point some¬ 
time after pasteurization. Therefore 
such determinations do not give 
any indication as to the degree of 
astringency a given juice will possess 
when it reaches the consumer, if pre¬ 
pared in the usual way. Their chief 
interest is through the indications 
such determinations may give as to 
the nature and extent of the effect of 
seasonal conditions upon the content 
of astringent constituents. It is a 
fact of considerable practical signifi¬ 
cance that juices which have been 
clarified by filtration with diatomace- 
ous earth by the methods described 
by the writer (17), do not undergo loss 
of astringency upon pasteurization. 
This method of filtration therefore has 
the merit, not fully appreciated when 
the paper referred to was prepared for 
publication, that it not only gives 
permanently clear filtrates but that it 
also preserves the juices from subse¬ 
quent alteration in their sugar-acid- 
tannin ratios. A detailed study of the 
chemical changes in apple and grape 
juices as a result of pasteurization is 
now being made as one phase of the 
investigations upon fruit juices in 
progress in this laboratory and will be 
published separately. A discussion of 
the effects of diatomaceous earth filtra¬ 
tion as related to pasteurization will 
be included in that paper, reference 
being made here by reason of its prac¬ 
tical importance. 
Tannin determinations upon fresh 
juices were not made in 1919 and 1920, 
so comparisons for only three seasons 
are possible. The data obtained in 
1921, 1922, and 1923 are presented in 
Table III. 
There are in the literature very few 
similar determinations with which 
comparisons may be made. Hartmann 
and Tolman determined tannin and 
coloring matter in the series of Concord 
juices studied by them, but these were 
hot-pressed juices, and the determina¬ 
tions were made after pasteurization, 
and hence are not comparable. Noyes, 
King, and Martsolf (53) made tannin 
determinations on Concord grapes 
throughout the harvest period, and 
Alwood and his collaborators (2) made 
similar determinations in their studies 
of ripening in Catawba, Clinton, Dela¬ 
ware, Ives, Norton, and Concord. 
The results in both these pieces of 
work indicate that the tannin and 
coloring matter fluctuate very irregu¬ 
larly throughout the ripening and 
harvest period, without definitely in¬ 
creasing or decreasing after the berries 
have begun to color. Tannin determi- 
