116 REPORTS ON THE STATE OF SCIENCE.—1918. 
IcH-CREAM. 
Ice-cream manufacture provides an interésting case of the prac- 
tical value of the so-called ‘ protective action’ of colloids. 
Alexander (J.S.C.Z. 28, 284 (1909) ) writes :—‘ It is a well-known 
fact to practical ice-cream makers and amply proven by experience, 
that ice-cream made without eggs, gelatin, or some similar colloidal 
ingredient, is gritty, grainy, or sandy, or else soon becomes so on 
standing, whereas ice-cream made with small quantities of colloids 
possesses that rich, mellow, velvety texture, so much in demand.’ 
(Cf. also Alexander (Zt. Chem. Ind. Koll., Feb., 1909).) 
Now ice-cream contains casein, and the action of the added 
(hydrophile) colloid is to ‘protect’ it from coagulating. Gelatin 
IS especially advantageous, and as little as 0°5 per cent. suffices to 
render the ice-cream smooth in texture. Incidentally, the diges- 
tibility is increased too by addition of gelatin. (Cf. discussion on 
the digestion of milk curd in the stomach.) Besides the protection 
of the casein, it is most interesting to note that the small ice crystals 
are also ‘protected’ by the colloidal binders added. An ice-cream 
having been whipped during freezing, contains numerous small ice 
crystals which on standing coalesce to form coarse grains. This 
coalescence is decidedly inhibited by gelatin, gum tragacanth, and 
starches, thus retaining the smooth texture so desirable in a first 
grade product. (C.f. Stocking ‘Manaul of Milk Products, Chap. 14, 
CEO AN): 
An interesting paper on ‘The Effects of Binders upon the Melt- 
ing and Hardness of the Ice-Cream,’ was published by Holdaway 
and Reynolds (Virginia Hapt. Stat. Bull. 211, 3 (1916) ). It is here 
shown that as the per cent. of fat in plain ice-cream increases, the 
cream becomes softer, and if too much fat is present a soft fluffy 
product results owing to ‘whipping.’ Ice-cream made from 8 per 
cent. cream was no harder than from 19 per cent. cream, while 
30 per cent. plain cream was much softer than either. The fat, 
however, raises the melting point. 
Now if gelatin be added a harder ice-cream results, With a 
higher melting point. The hardest and most heat-resisting cream is 
given by a medium per cent. of fat and a large amount of gelatin. 
Gum tragacanth (also a protective agent) may be used, in which case 
the ice-cream produced is harder. than usual (plain) but softer than 
when gelatin is used. One would expect this result, since the 
protective powers of the two colloids are very different, as will be 
seen by a comparison of their gold-numbers, viz.:— 
Gelatin fie a = ... 0°005 to 0-01. 
Gum tragacanth ... iH ... about 2:0. 
If too much gum tragacanth is used, a very slimy cream results; in 
any case it is far inferior to gelatin ice-cream of any composition. 
Some manufacturers use starch as the agent to ‘smooth’ their 
ice-cream, but although a better product than normal (plain) cream 
results, the texture is much more grainy than the ice-creams contain- 
ing gelatin or gum. One expects this to be the case, since starch is 
only a poor protecting colloid, the gold value of wheat starch being 
about 5, and of potato starch about 25. 
