September 12, 2015
Although unknown to most people, citrus oils are a significant industry to themselves. Historically, Vincent screw presses in citrus feedmills have been a key component in the recovery of d-limonene. That is the "lemon oil" (actually it comes from oranges) everyone has smelled in industrial hand cleaners. It is a valuable by-product produced in the WHE (waste heat evaporator) which is used in large feedmills to produce citrus molasses.
Our screw presses have found application in Mexican lime and lemon processing plants. These facilities squeeze fresh fruit or peel, without the use of hydrated lime, to separate an emulsion-like flow from the peel. This emulsion contains citrus oil which can be separated in a calandria (still). Forty years ago Vincent designed and sold calandrias. Today JBT offers a stand-alone, skid-mounted READYGo™ d-LIMONENE system to recover d-limonene from oil-rich emulsions generated in the citrus extraction process.
The Cook Machinery Company of Dunedin, Florida has pioneered and led in the development of d-limonene and citrus essence oil recovery for many decades. JBT has been a key partner in their activities. Brown International is another key player in the industry.
Major processors of citrus oils include Firmenich and Givaudan. The Coca Cola Company purchases over half of all the lemon oil produced worldwide.
An overview of citrus oils follows.
Higher quality oil is more valuable as it contains more flavor and fragrance components. Usually this oil is not heat treated and has minimal contact with the fruit and water. Globally, high quality oil is purchased by flavor and perfumer houses for further refinement. Lower quality oil is less valuable and usually sold on the secondary market.
There are several of different types of commercially produced citrus oil:
The first type is cold pressed oil, or peel oil. This oil is extracted, without heat, from citrus peel. Oil is expressed from the peel and captured in water. Usually either Brown or JBT (FMC) extractors are used to express the oil from the fruit, although other types of extractors can be used. The resulting oil and water emulsion is sent to a series of centrifuges to separate the oil and water. GEA Westfalia and Alfa Laval are usually the OEMs for this equipment.
Oil produced this way is eventually fractionated into flavor components and d-limonene, using a complex distillation column. The phase separation process is described as folding oils. The flavor fraction is the more valuable component, and usually it is between five percent of the oil for some types of non-Valencia oranges up to 45% to 55% of the oil for limes. The balance of cold pressed oil is d-limonene. D-limonene is less valuable, but it has several uses including as a solvent and as an ingredient in cleaners.
The next type is essence oil. This oil is entrained in juice extracted and finished by juice extractors and finishers. Again, JBT (FMC) and Brown are the main providers of the extraction equipment, although some smaller companies also provide machines. Essence oil is captured by essence units installed on juice evaporators. These essence units also recover a water phase essence. Both oil phase and water phase essences contain flavor components. Oil phase essence can be particularly valuable to flavor and fragrance companies. Water phase essence can also be used in flavor applications, but this phase is more unstable and can degrade rapidly.
An essence-type oil archaically known as Wheeler oil is recovered from juice after juice extraction and finishing. This oil is also called juice oil. Centrifuges are used to separate this oil from the juice. No heat is used. This type of oil is not commonly produced because there is not a lot of it, mass-fraction wise. Wheeler oil is unique and has valuable flavor components due to the oil's extended contact with the juice.
A fourth type of oil is d-limonene, which is made in citrus feed mills or in distillation processes such as JBT’s READYGo d-LIMONENE unit. D-limonene is not really an oil, but a component of oil. This product is made when liquid pressed from citrus peel is concentrated in a WHE. The d-limonene is stripped from the press liquor in the WHE. Any oil or water phase essence contained in the press liquor is flashed off in the evaporator and not recovered. D-limonene recovered in this traditional system requires a full-scale feed mill, including hammer mill, lime addition and reacting screw, screw presses, dryer, waste heat evaporator, and pellet mills.
Note that lime oils are a little different. Three types of oil can be produced from whole lime fruit crushed by a screw press. Both oil and juice are expressed from the press, and peel and membranes are expelled separately. Centrifuges are then used to separate Type A lime oil from this juice and oil slurry. No heat is used to produce Type A oil. Distilled lime oil is usually produced from the oil remaining in juice exiting the centrifuges, but juice and oil directly exiting the press can also be used. For distilled lime oil, processors use steam in a still, a condenser, and a separator. Type B lime oil is cold pressed oil, extracted and separated like other cold pressed citrus oils mentioned above.