MAKING USE of TONS of CITRUS WASTE 269 Total of 10 to 12 Percent Soluble Solids
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Making Use of Tons of Citrus about 8 percent moisture, 6 percent ash, 6 percent crude protein based on total nitrogen, 6 percent crude fat, 14 percent crude fiber, and 66 percent Waste nitrogen-free extract. Although it must be supplemented with some other feed, Harry S. Owens, M. K. Veldhuis, it contains significant amounts of pro- W. Dayton Maclay tein, fats, and minerals. To make dried pulp, fresh peel is first ground in a hammer mill. One- half to 1 percent of lime is added to More than 2 million tons of pulp, the peel immediately after grinding; peel, and rag remain caeh year after the amount is carefully measured in citrus fruits are processed into juice, order to get the best pressing character- frozen concentrate, and sections. What istics. The lime neutralizes the acids to do with those mountains of waste? and catalyzes the de-esterification of When the industry was young, the the pectin in the peel to form calcium only wastes were the culls and surplus pectate, which facilitates pressing and fruit, which were dumped on w^aste- drying. Formerly the peel was allow^ed lancl or used as soil conditioners on to stand in bins for about 45 minutes cultivated land. Solid wastes from early before pressing or drying to allow time canneries w^erc handled in the same for the lime to react. Now the time of way. The liquid wastes were ponded or reaction is shortened to 15 minutes or flushed into streams, lakes, or sewers. so by stirring the peel constantly as it All such makeshifts were unsatisfac- moves slowly through a pug mill. Con- tory and dangerous. A pile of rotting tinuous presses remove as much liquid orange peels soon begins to stink; as possible. In some processing plants underground water supplies are con- the pulp is heated by direct steam in- taminated ; and the increased biochem- jection to about 120° F. during this ical oxygen demand kills acjuatic life step to facilitate the pressing. The or exceeds the capacities of sewage- weight of liquor removed is about equal treating plants. to the w^eight of the pressed pulp. Industrial, State, and Federal re- Direct-fired or steam-heated rotary kiln search organizations investigated the driers are used to remove the moisture increasingly serious problem. From from the pulp. In some mills the pulp their efforts came several economically is given a preliminary drying in direct- valuable products. Now 80 to 90 per- fired units and finished in steam- cent of citrus wastes are converted into heated units. Careful control of the usable products, such as dried pulp, drying rates and temperatures is neces- molasses, pectin, essential oils, brined sary to produce the fluffy, light-colored peel, citric acid, limonene, feed yeast, feeds that are considered desirable. and biologically active materials. About 1 ton of feed is obtained from 10 From the waste peel, marc, and seeds tons of cannery waste. In the past 10 that came from the processing lines, re- years, production of dried peel has in- search men developed dried pulp, creased to approximately 200,000 tons which is used extensively for feeding a year. dairy and beef cattle and is suitable Press or drain liquor from citrus peel for feeding other animals. It contains contains 5 to 7 percent sugar and a 268 MAKING USE OF TONS OF CITRUS WASTE 269 total of 10 to 12 percent soluble solids. show^ed an average of 71.4 percent It cannot be flushed into sewers or total solids, 42 percent sugars, 3.8 per- ponded unless care is taken to reduce cent crude protein, 1.1 percent pectin, the biochemical oxygen demand or to and 4.8 percent ash. The pH value prevent bad smells. Most of the press was 4.7. liquor is concentrated to produce mo- Citrus molasses is dark brown and lasses. Multiple-effect evaporation is bitter. It is used mainly in cattle feeds, commonly used. One plant in Texas in which it is usually mixed with other uses direct heating with a submerged materials, although it can be fed full- gas flame, followed by tw^o stages of strength. Som.e is mixed with wet citrus evaporation. pulp and then dried to make a feed. The first stage of a multiple-effect The amount of total digestible nutri- evaporator is operated under positive ents in the molasses is about 57 percent. pressure (up to 26 pounds) and the Some is used as a fermentation sub- last stage under negative pressure strate in the production of alcohol. (down to 26 inches of mercury). Inter- Production of citrus molasses in- mediate stages may be used to increase creased from none in 1940-41 to nearly the number of pounds of water evapo- 42,000 tons in the 1949-50 season. rated per pound of fuel consumed. Evaporators may be constructed of ANOTHER USE for press juice is in the mild steel. Corrosion is something of production of yeast, particularly Toril- a problem if not all of the acid is neu- lo psis utilis, which grows rapidly and tralized by the lime, A more serious is therefore less susceptible to contam- problem is scaling of the heat-ex- ination than other yeasts. It is rich in changer tubes in the evaporators, be- vitamins of the B complex and is a cause the scale builds up rapidly, inter- good supplement in feeds. About half feres with heat transfer and circula- the dried yeast is crude protein. It is tion, and must be removed about twice deficient in methionine, one of the es- a week by boiling with lye. The exact sential amino acids, which, however, nature of the scale has not been deter- is present in cereal proteins. A ration mined, but it probably is composed containing this yeast with some cereal largely of calcium citrate, calcium pec- would provide all the essential amino tate, and fibrous material. Trouble is acids. encountered primarily in the first effect Research workers in the Southern of the evaporator. Some operators give Regional Research Laboratory, the the press juice a preliminary heating United States Citrus Products Labora- to 212° F. or higher in an auxiliary tory in Winter Haven, Fla., and a com- heat exchanger, which can be cleaned mercial cannery worked together to easily. The heating precipitates some develop a process for the production material, which is removed in a con- of feed yeast. Their experiments in- tinuous clarifier, and lengthens the cluded the operation of a 200-gallon- time the evaporators can be operated per-hour pilot plant. They developed between cleanings. a continuous method, which gives a In a recent installation, submerged good yield. The juice from the feed mill gas burners are used to give the press is first passed through an 80-mesh juice a preliminary heating and con- screen to remove particles of pulp. centration to about 22 percent solids. Then it is diluted with water to a sugar Carbonation by the products of com- concentration of about 2 percent, bustion forms a precipitate, which is heated to 200° F. to destroy micro-or- removed in continuous thickeners. ganisms, cooled, and pumped contin- Either method reduces the amount of uously into the yeast propagator. A suspended matter in the final product concentrated nutrient solution is me- and improves the quality. Analyses of tered into the propagator in proportion 13 samples of Florida citrus molasses to the feed rate. The propagator is 270 1950-1951 YEARBOOK OF AGRICULTURE kept thoroughly aerated by air intro- crude protein and 3.3 percent phos- duced through porous stone candles in phate (as the pentoxide). The product the bottom of the tank. The product is light in color, fluffy, and, though not from the propagator flows continuously w^ashed, only slightly bitter. into a collecting tank and thence to special centrifuges which separate the THE ISOLATION OF OIL from the rind yeast as a thick cream. The yeast cream of the lemon is one of the earliest chem- is dried on a drum drier, pulverized, urgic applications of citrus fruit. Hand and packaged. pressing of the peel against sponges has As nutrients, phosphates and nitro- been practiced in Sicily since the 18th gen compounds must be added. Some ce:ntury; at one time the United States benefit can be obtained from the phos- im]:)orted nearly a half million pounds phorus in the juice, but it must be sup- of lemon oil annually. Machinery has plemented. AlDout 0.19 pound of am- made possible the production each year monium sulfate, 0.045 pound of of more than 1,500,000 pounds of oils anhydrous ammonia, and 0.045 pound from citrus peels. of 75 percent phos]Dhoric acid are re- The whole fruit, waste cannery peel, quired per pound of yeast. The acidity or flavedo, the colored part of the peel, in the propagator is easily controlled can be used. The material is ground within the range of pH 4 to 4.5 by and pressed in screw extractors or varying the ratio of ammonia to am- pressed between fluted rolls to yield an monium sulfate. With the method of oil emulsion. A recently developed aeration used, from 500 to 700 cubic juice extractor, which presses the feet of air w^as required per pound of whole fruit, delivers separately the yeast produced. Cooling coils w^ere in- edible juice and an oil emulsion. The stalled in the propagator to dissipate emulsion is screened and the oil sepa- the heat of fermentation and maintain rated by centrifuging. The centrifuged a constant temperature of 95° F.