26 BULLETIN 1370, U. S. DEPARTMENT OF AGRICULTURE 
and is fairly well cleaned. As the sirup becomes more concentrated, 
more flocculated material separates. This should be carefully re- 
moved by skimming. Although not absolutely necessary, the skim- 
ming troughs, divided into two parts, should, for convenience, extend 
the full length of the pan. Such troughs are inexpensive and easily 
constructed. For efficient skimming, a hot fire must be maintained to 
“roll” thefoam. ‘The fireman can easily remove skimmings from the 
cool end of the pan, in this way greatly assisting the sirup maker. 
Firing at the proper time, however, should be his main consideration. 
Scorching thick sirup is a difficulty sometimes experienced in open- 
pan evaporation; such sirup acquires a red color and a burnt flavor. 
Scorching is accompanied by a white puff of vapor, and can always be 
detected by careful observation. Experienced sirup makers detect it 
by odor almost instantly. Scorching is caused by local overheating 
at portions of the pan where the sirup has reached high density. 
Sometimes poor furnace construction is the cause of this; sometimes 
the sirup has become too concentrated. Sediment adhering to the 
bottom of the pan may readily result im a scorching area. Such 
scorching may be stopped by thoroughly seraping the surface over 
which it occurs with a piece of metal (galvanized iron or copper) 
fastened to a handle. In case the sirup is of too high density at the 
point where the scorching occurred, sirup of lower density should be 
forced in from the next compartment. 
In operating a continuous evaporator, the fiow of juice should be 
kept as nearly constant as possible without dipping from one com- 
partment to another. Such dippmg detracts from the clarity of the 
sirup, owing doubtless to the mixing of juice and sirup at different 
stages of clarification. This mixing of high and low density sirup 
usually causes a persistent cloudiness in the finished product. It is 
a good pian to divide the skimming trough mto two sections by 
means of a transverse partition, to avoid mixing the clarified sirup 
with the juice. Even if no injurious effect on clarity or color should 
result, it is useless to again subject well-skimmed semisirup from the 
finishing end to the skimming process. It is little trouble to.divide 
the trough into two sections and to make suitable holes, through 
which the overflow may return to the pan. 
One of the difficulties most commonly experienced im using a 
continuous evaporator is that of concentrating the sirup to uniform 
density. Many operators are able by experience to judge accurately 
the density of sirup while it is still boiling. They do this by dipping 
the skimmer into the boiling sirup, holding it up, and noting how the 
cooling sirup “‘fiakes off.’? No amount of experience, however, can 
entirely take the place of accurate knowledge, and the uncertainties of 
guessing the density by the “‘flaking-off’’ method can be easily elimi- 
nated by the use of a thermometer. A good thermometer is more 
useful in the operation of an evaporator than is the hydrometer, often 
recommended for the purpose. In using the hydrometer it is neces- 
sary to draw off a cylinder of sirup from the evaporator and then 
float the hydrometer in it. This procedure is troublesome when 
using an evaporator, because the sirup is in such a shallow layer that 
it is not easily. dipped out. The hydrometer, although very useful 
when sirup is made in a deep evaporator by the batch or noncontin- 
uous process, is considered less valuable than a thermometer for use 
with the ordinary continuous evaporator. 
