This is similar
to the basic wood-fired evaporator, except that it uses economical
fuel oil as a fuel source. Sap (either fresh sap or pre-processed)
enters the evaporator pan where it is heated, water is released as
steam, and the finished syrup is drained off.
Generally, there
are two evaporator pans. Fresh sap enters the sap or flue pan. It
has narrow, deep channels to improve heat transfer from burning the
oil. More concentrated sap then flows into the flat-bottomed syrup
pan. The flat bottom allows shallow layers of thicker sap to evaporate
with little danger of burning.