l'be granulating-point Is easily recognised by a practical pan-boiler: a "proof" of the syrup, taken between the thumb and finger, should draw to a thread 11-in. long; but this test is of no value if the syrup is sticky, resulting from under-tempering or sour caues.
In boiling for large grain, it is essential to grain low. The grain commences to form in minute specks ; these rapidly increase in number and size, until the whole mass of liquor is filled with them. As each lot of syrup is admitted, it deposits on the grains already formed, causing these to grow larger. During granulation, the temperature should never be more than 71°-78° (160°-172° F.), though raised later on to harden the crystals ; but this must not be done too soon after graining, or the crystals will melt.
Rules for graining syrup in the vacuum-pan are :—The thinner the syrup admitted, the bigger will the crystals be ; for large-grain sugar, few and heavy charges must be admitted, so as to give 1369.
the grain time to grow ; the larger the crystals are required, the more quietly and slowly must the boiling be carried on ; to make regular grain, granulation is brought about very slowly, and on no account must the grain be forced by boiling very Ligh before the first charge.
It is important in pan boiling to avoid forming " false grain." The two stages when the danger of it is greatest are :—(1) The time when the sulphuric acid (for producing " yellow crystals ") is admitted into the pan ; (2) the " opening " of the sugar when re-starting the pan to " double," e. when, having struck out half the contents of the pan, fresh portions of syrup are admitted on to the masse-cuite left in the pan. If the contents are not sufficiently high when sulphuric acid is admitted, false grain fornis whilst working up for striking. Unless the masse-cuite be "opened " very slowly, the new lot of syrup, instead of depositing on the already-formed crystals and increasing their size, will form an independent grain, called " false grain," which not only spoils the sugar, but prevents the molasses leaving it in the centrifugals.
When false grain is very bad, the best course is to strike it out immediately, and spin it in the centrifugals, mixing it with warm water if absolutely necessary. When not very bad, and
the rsim is little more than half-full, the heat and washing of a few heavy charges of new syrup will remove it.
Demerara " yellow crystals."—Sulphurio acid imparts to the sugar the delicate yellow bloom so much admired in " Demerara crystals," instead of the ordinary green-grey colour. If too little is mixed -with the masse-cuite in the pan, the colour is scarcely improved ; if too much, the sugar turns quite red a day or two after curing. lt is admitted last of all ; pan-boilers should not be allowed to make a charge of syrup on to it immediately previous to atrikinz. The quantity of acid to be used depende on the colonr of the masse-cuite ; as a rule, 3 gal. of acid diluted with 14 gal. of cold oondeneed water to 5 tone of augar is about right. In all cases, the least possible quo.ntity should be used compatible with securing the desired result.
The proper striking-point ie of great importance, and arrivea when the proof will scarcely run out of the socket of the proof-etick. Masse-cuite on leaving the pan ehould have a light-red colour tinged with gold, and a temperature of 66° (150° F.)—never higher. The objects of doubling are to increase the size of the grain, so that the market value of the sugar may be enhanced, and to eavo time. Some eyrup makes sugar that will bear doubling 2-5 times; while some gets sticky after the 1st cut of the pan. Great care must be taken while opening the masse-e,,,/e left in the pans ; for tho 3rd or 4th cuts, a temperature of 74° (165° F.) may be maintained while opening elowly and carefully, the operation requiring 15-25 minutes. The drawing-in of eyrup deinauda more care in aubaequent cuta than in the first.
Great loss of augar is caused by doulding, depending on the amount of acid used, and nn the quality of the ayrup ; it ia estimated to amount to 20-25 per cent. of the augar, and some hold that a better return is obtained from the larger quantity of dark auger at a lower price ; hut on the other band the " tom " means augar converted into a high class " golden syrup," and the extra market value of the yellow cryatale is affirmed by some of the beat authorities to more than atone for the extra coat and increased invereion of crystallizable sugar.