Citrus Molasses

November 19, 1998

In the states of Florida and Sao Paulo in Brazil all citrus juice extraction plants have citrus peel feedmills that produce citrus molasses. This molasses is made from the press liquor that results from pressing orange peel. The molasses is produced in waste heat evaporators (WHE) that are driven (heated) by the exhaust gasses from the cake dryers. Typically the molasses are concentrated into the range of 40º to 50º Brix and they are either sold to a distillery or re- combined with the peel. If the molasses are to be stored for more than a few days, they are concentrated to 72º Brix as fermentation will not readily occur at this high a sugar content.

Many smaller citrus processors in other countries process their peel into animal feed without producing citrus molasses. The technology they use is to either (a) simply dry the peel from its natural 80% moisture to 12% in a rotary drum dryer, or (b) press the peel from 80% to about 72% moisture and then put the cake into the dryer.

Those processors who simply dry their fresh peel find themselves at an economic disadvantage because it takes a great deal of energy to evaporate all of the moisture. Using a WHE, larger firms will use as little as one third as much energy to produce a ton of citrus pellets.

Those processors who use a press in front of the dryer fare better. Pressing from 80% to 72% moisture separates over half of the water from the peel. (It also results in the loss of almost one third of total solids because of the dissolved sugars that are carried away with the press liquor.)

However, the processors using a screw press face a serious environmental problem. Most of these, in Greece and Panama for example, send the press liquor to the sewer. The high sugar content of the press liquor (10º to 12º Bx) puts a high load on the wastewater treatment system. Odor and pollution complaints result in government pressures.

Acquisition of a WHE is out of the question for most small processors. Typically the WHE is the single largest capital item in a citrus processing plant. Furthermore, the dryers existing at many small processors are not suitable for generating the high wet bulb temperature gasses necessary for the proper operation of a WHE.

An interesting alternative exists for these small processors. Instead of a WHE, they can use a steam evaporator to produce molasses from their press liquor. A vertical tube evaporator, using falling film heat transfer, represents less capital investment yet it can be very effective in making citrus molasses. For example, the steam ratio is approximately 5:1 for a six effect evaporator. This means that for every pound of steam used to drive the evaporator, five pounds of water are evaporated from the press liquor.

The citrus molasses produced can be used as cattle feed or sold to a distillery. As a cattle feed, the molasses can be supplied to the farm in a liquid form. It is more common to add the molasses back onto the peel. The solids are diffused into the moisture in the peel, and the moisture is ultimately evaporated in either the dryer or the evaporator.

Distilleries buy molasses in order to ferment it in the production of citrus alcohol.

An important by-product is d-limonene, an oil that comes from the citrus peel. This oil is recovered in the evaporator. d-Limonene adds to the revenue stream used to justify the acquisition of an evaporator.

Issue 86