March 31, 2009
Updated December 2023
One of the by-products of a citrus processing plant is known as “pectin peel”. Production of pectin peel involves washing the sugars and oils from the peel and then drying the peel at low temperature. The dried peel is shipped to companies which use an acid-alcohol precipitation process to extract the pectin. The pectin produced in this manner is sold world-wide as a food ingredient.
This processing of pectin peel is an area of technical expertise of Vincent Corporation. For many years we designed the plants and manufactured the machinery that is required. Today we offer only our applicable specialty machines, screw presses, shredders and Fiber Filters – along with free advice.
Historically, pectin peel was made from lime or lemon peel, with lesser amounts made from grapefruit and orange peel. In recent years the use of orange peel, especially in Brazil, has grown exponentially.
The dried peel is sold to firms such as CP Kelco in Denmark, Germany, and Brazil; Cargill in Germany, Italy, France, and Brazil; IFF in Mexico; Herbstreith & Fox in Germany; and Yantai Andre Pectin in China. These firms, in turn, extract pectin from the peel, for sale as a food additive.
Pectin peel generally sells in the range of US$ 300 to $600 per short ton. [April, 2015: It is now around $2,000 a ton!] This can be compared to selling pelletized citrus peel, for animal feed, where the market is in the range of US$ 50 to $100 per ton (in the United States).
The process of producing pectin peel revolves around washing the peel in water so as to diffuse out the soluble sugars. Normally about 3 kilos of fresh water are required to wash one kilo of peel. In advanced systems, only 1.25 kilo of water is used per kilo of peel.
This contrasts to drying citrus waste to make animal feed, in which the first step is to react the peel with lime. Hydrated lime degrades the pectin, releases the bound juices, and thus permits efficient pressing and dehydrating. In contrast to this, the production of pectin peel must preserve the pectin; therefore lime cannot be added to it.
As a consequence of the washing process, the peel becomes very slippery and difficult to press (dehydrate). Accordingly, in pectin peel applications, we de-rate the capacity of our screw presses by 50% or more.
Further, pectin peel must be dried very carefully at low temperatures and with carefully controlled humidity. The Vincent-design rotating drum drier was the norm for the industry; however, we withdrew from the dryer business in 2007. That dryer permitted recirculating some of the partially dried peel and mixing it with the material coming from the screw press. The design was a triple pass dryer with a stationary outer shell, which contrasts to the single pass rotating drum dryer most commonly used in the production of animal feed.
Processing plants where Vincent, over 50 years, installed pectin operations include Ci Pro Sicilia and Cesap in Italy; Laconia, Paco Hellas, Nikopolis (ex-Esperis) and Greek Juice Processing in Greece; Citrex and San Miguel in Argentina; Quimica Hercules, Productos Esenciales, Industrial Citricola, and Industriales Limonera in Mexico; Jn-Jacques and Moscoso in Haiti; Priman Canning and Yahkin in Israel; Avante in Brazil; and Unipektin in Morocco.
Currently there are no processors producing pectin peel in the United States: Ventura Coastal and Sunkist in California, and Parman Kendall in Florida, have all discontinued their peel washing operations. Environmental considerations, especially disposal of the sugar laden, used wash water, were driving factors.
Typically we look at peel coming from juice extraction in the range of four tons of peel per hour on the low side and sixteen on the high side. More recently flows of 26 MTPH have been of interest.
The following equipment is key to the process:
Vincent VS-18 Shredder. This machine uses a discharge screen which determines the particle size which is achieved. Screens with different sized openings are used depending on the variety and maturity of the fruit.
Pulp Wash Conveyors or Tanks. These are used for diffusing the sugar from the peel. We recommend either three or four counterflow wash stages, in either vertical or horizontal configuration.
Pulp Wash Sumps. Stainless steel sump tanks, with Moyno or progressive cavity peel transfer pumps.
Dewatering Between Stages. We recommend the use of either static screens or rotary drum screens for dewatering between wash stages. Water usage is reduced by pressing the solids from these screens with Vincent Series KP “soft squeeze” presses.
Vincent Screw Press. Traditionally the Series VP presses were used to remove moisture from the peel prior to further dehydration in the dryer. Oversize, low speed KP presses have proven to be a more economical alternative.
These presses use a horizontal configuration, with all liquid contact parts made of stainless steel. The screw features multiple stages of compression with an interrupted flight design. The units are equipped with an air cushioned cone, complete with pneumatic controls. Rotating cones are used on the single screw machines.
The pectin peel is made from the cake, which usually comes out in the range of 80% to 86% moisture, depending if we are talking about Italian lemon, Persian, Limon Mexicano, Tahitian, Key limes, grapefruit, or orange peel.
Furnace. The dryer comes with its burner and refractory lined furnace for burning natural gas, light weight fuel oil, or a combination of these fuels. A very low gas temperature, in the neighborhood of 1200º F or less, must enter the dryer. A low wet bulb temperature is important in the production of high quality pectin peel, whereas a feedmill dryer must produce high wet bulb temperature in order to drive the Waste Heat Evaporator.
Dryer Feeder. This is a stainless steel screw conveyor and feeder with a companion flange matched to the dryer throat. It has a variable speed drive.
Dryer Drum. A triple pass dehydration unit with a stationary outer drum works best. The unit is equipped with recycle extractor conveyors so that partially dried material is extracted at the end of the second pass and mixed with the incoming press cake. Also important is a 180º elbow between the furnace and the inlet to the drum. The selection of this dryer must be made using the appropriate de-rating associated with (low temperature) pectin peel production.
Exhaust System. This separation system features a low level entry cyclone separator that has been proven in producing pectin peel. The expansion chamber is complete with an air lock screw conveyor product discharge.
Exhaust Fan. The induced draft fan has radial blades with inlet elbow and exhaust stack.
Standard Instruments. A solid state programmable controller modulates combustion through a sensor mounted at the inlet to the third pass of the dryer. This is required for precise control of product quality.
Cooling Reel. The cooling reel uses ambient air for final drying. It is complete with a fan, dust collector, ductwork, supports, and electric motors. An important function of the cooling reel is to remove black specs from the flow of dried peel.
Product Elevating Screw and Surge Hopper. A carbon steel conveyor and hopper, leading to the bagging or baling equipment, are used.
Baler. Balers are used to compact the peel into 50 kilo bags. These bags are stacked in cargo containers for transit to European pectin factories. The bags are roughly 370 x 370 x 830 mm.
Sewing Head and Bagging Scale. Most pectin peel is baled, so that a maximum amount can be loaded into a cargo container. If bagging is used, a Fischbein sewing head and conveyor with a bagging scale are typically included.
Despite the length of this newsletter, there are a great many details that have been left out. We would be glad to work with your specific requirements.
Robert B. Johnston, P.E.
ISSUE #209