During evaporation much of the aroma (or essence) is stripped from the juice as it is being concentrated. It is generally desired to recover a high quality (little damage from heat or oxidation) essence fraction. Essence is considered to be those naturally occurring compounds which form the fraction lighter than water vapor (Some of the essence compounds actually have a lower volatility than water, but are steam distilled and end up in the volatile fraction). This fraction is concentrated in the evaporator and essence system by distillation. Then it is refrigerated to condense the most volatile compounds. The liquid drains by gravity to a decant tank. The essence will naturally divide into two phases. One phase is the aqueous phase and the oil as the oil phase. In the decant tank, gravity separation of the oil and water is accomplished by the fact that the oil phase will float on top of the water phase. A second finishing step of centrifuging is sometimes employed. Essence recovery should be integrated into the evaporator design. The tube bundles need to built to facilitate the collection and concentration the aroma vapors before the essence recovery system. A “mixed” flow evaporator is best for the recovery of a high quality essence. By having the first stage at a lower temperature there is less heat damage and oxidation of the essence compounds. The essence bearing vapors are “boiled-off” with the water vapors. The vapors are condensed in the shell side of the of the following stage. The essence bearing vapors rise toward the top of the shell side and pass through a series of baffles in the tube nest designed to remove as much condensate water vapor as possible. The noncondensed portion of these vapors are removed through the vent line at the top of the tube nest and pass to the essence system. There are two principle essence recovery systems in the Florida citrus industry. Dr. Redd’s essence recovery system and the Cook essence recovery system. Details of the essence systems will be discussed later. The strength of the aqueous phase of the essence is measured by the alcohol concentration in proof. That is 20 proof essence has 10% alcohol. The oil phase is mostly d-limonene. d-limonene is a component of the peel which thru extraction ends up in the juice. The oil phase of the essence is sent to an oil house, where an oil still is used to increase concentration of the non d-limonene compounds. The amount of essence collected is expressed by the fold. Typically a 400 to 500 fold is accomplished. The fold is the ratio of juice feed to essence collected. PROBLEMS WITH ESSENCE SYSTEMS You should always remember that essence system depends upon a well functioning juice evaporator. The number one problem is air leaks. The air that is vented into the essence system takes the place of some of the essence vapors. The number two problem is hardware. Disrepair, broken valves, broken refrigeration controls, improper refrigeration control settings. High alcohol fruit (very ripe) can be a problem. During late May and June the fruit can get old and start to spoil thus producing a lot of alcohol. With this large amount of alcohol you will need to open the product valve thus collecting more essence. If the essence becomes too strong then you will be losing a portion of the essence and the performance of the evaporator may be reduced. If the alcohol concentration is too high it can cause problems in the decanting of the oil phase. As alcohol concentration increases the aqueous phase becomes closer in density to that of the oil. And you sometimes may see some carry over into the oil phase. ESSENCE CONCENTRATION Essence concentration is controlled by adjusting the reflux. This is done by opening or closing the essence valve. The desired concentration for essence is about 24 proof. The amount of essence available varies greatly in the amount and quality during a season. The greatest amount and best quality essence is collected during the Valencia season. CLEAN UP When cleaning the evaporator the essence flow should be diverted. This will prevent the collection of “aroma of caustic” and “aroma of clean-up water”. COOK ESSENCE SYSTEM The Cook essence system is integrated with the evaporator. The vapor baffling in tube bundles is arranged to push to essence compounds toward the essence recovery unit. The essence condensers are part of the juice preheating circuit, thus recapturing the heat loss with the condensing. There is a great effort made to recover the maximum amount of essence. The vents go to the essence system. Where they are too weak, they are recycled to be concentrated and then collected. The condensate is scrubbed to reduce the loss in the condensate. Fractionating condensers provide the distillation and thus the concentration of the essence. Ammonia cooling is used to capture the most volatile compounds. REDD ESSENCE RECOVERY SYSTEM The Redd essence system uses the vent from first boil off, usually the first effect. The vapor goes into a distillation column with a reboiler at the bottom and a reflux condenser at the top. From the reflux condenser a small flow is taken off and cooled in an ammonia chilled condenser. Another two ammonia cooled condensers are used in series to condense the most volatile compounds from the vapor.