48 BULLETIN 1870, U. S. DEPARTMENT OF AGRICULTURE 
MILLING PLANT 
Some plants, especially the small ones, have only one 3-roller mill. 
Others have a 2-roller crusher and a 3-roller mill. Another in- 
stallation consists of one 2-roller crusher and two 3-roller mills. 
Sometimes (in sugar factories) as many as seven mills are used with 
one crusher. In some sugar factories two crushers are used with 
as many as six 3-roller mills. | 
The object of using several milling units is to increase the extrac- 
tion of sugar from the cane and at the same time produce bagasse 
sufficiently dry to be burned efficiently. Higher extraction can be 
obtained with a crusher and one or two 3-roller mills than with one 
3-roller mill. When only one 3-roller mill is used the extraction is 
low and the resulting bagasse, which usually contains too high a 
percentage of moisture to be burned efficiently, is discarded. When 
a crusher and two mills are used the crusher prepares the cane by 
partly crushing it before it reaches the first mill, thereby making it 
ossible for the first mill to express more juice. Upon leaving the 
t mill the bagasse may be partly saturated with water before 
entering the second mill. The purpose of this process (maceration) 
is to dilute the juice remaining in the partially ground cane, thereby 
facilitating its extraction by the second mill. 
The process of maceration may be extended and water may be 
applied to the bagasse before it enters the third mill (when a third 
mill is used), a still greater proportion of the juice being thus .ex- 
tracted. Sometimes, in order to reduce the fuel consumption re- 
quired to evaporate this added water, dilute juice, perhaps from the 
last mill, is pumped back and used for maceration on some of the 
preceding mills. Adequate equipment is necessary for high extraction. 
The importance of high extraction in large-scale operation is 
indicated by the fact that 1 per cent increase in extraction, when 
grinding ordinary Louisiana cane, yields one-third gallon more of 
sirup per ton of cane. When grinding 200 tons of cane per day for 
a 60-day season the additional sirup thus obtained would amount to 
4,000 gallons, which, at $0.50 per gallon, would be worth $2,000. 
High extraction also makes it possible to utilize the bagasse as fuel. In 
obtaining the highest extraction, however, it is necessary to use Water 
for maceration, and evaporation of this water requires increased fuel 
consumption. The cost of evaporating this water would have to be 
subtracted from the $2,000 to determine the net gain. 
Owing to their acidity, juice and sirup dissolve iron, which darkens 
the sirup. For this reason juice and sirup should be exposed to iron 
surfaces as little as possible. The clarifying tanks and settlmg 
tanks may be made of sheet iron if they are kept well coated with a 
special heat-resisting paint. It is impossible to make a high-grade 
sirup if these precautions against contamination are not observed. 
The surface of the mill rollers is the only iron material with which 
the juice should be allowed to come in contact. Clarified juice should 
be evaporated to sirup in copper vessels. Copper evaporators of 
the Louisiana type are best, but satisfactory evaporators have been 
made of heavy yp! ess lined with copper sheeting and provided with 
copper heating coils. 
