Making sugar from sugarbeets in the Northern Great Plains
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By David Graper
SDSU Extension Horticulture Specialist
Edited from the Southern Minnesota Beet Sugar Cooperative website: http://www.smbsc.com/default.aspx
The sugar process
The following information shows how the sugarbeet becomes beet sugar; factories may vary slightly, but the process is basically the same.
The process involved in the production of sugar from sugarbeets is not truly a manufacturing process but rather extracting the sugar (sucrose) manufactured by the sugarbeet itself from sunlight, water, and nutrients in the soil. The sugar is stored within its root at a concentration averaging from 10 to 20 percent, depending upon the variety of beet planted and the weather conditions experienced while growing.
The manufacturing processes are really just a series of physical and chemical separations and processes designed to extract the sucrose from the other soluble and insoluble materials produced by the beet during its growth cycle and from the weeds, dirt, and beet tops left adhering to the beets during harvest.
Planting and growing sugarbeets
Planting of the sugarbeet crop begins in mid to late April of each year. Shareholders plant varieties, which have been previously tested and approved for planting. Sugarbeet varieties are approved based upon the varieties ability to meet or exceed a minimum standard for both extractable sugar per ton and extractable sugar per acre.
Planting a sugarbeet field
Sugarbeet seedlings begin emerging from the soil 10 days to two weeks after being planted. Sugarbeets are very susceptible to wind damage, chewing insects and seedling disease until they reach the 4-6 leaf stage. At this time, they become very hearty and will survive many weather extremes. Herbicides are applied to sugarbeets to control weeds until the sugarbeet canopy becomes large enough to shade the area between the rows. Once full canopies are established (July 1), weed pressure and competition with the sugarbeet is greatly reduced.
Harvesting sugarbeets
When the beets are first harvested in early August and September, they are delivered directly to the processing plant. This limited harvest allows shareholders to open roadways through fields in preparation for the main harvest, which begins October 1. Beets harvested later in the season are stored in large piles. Shareholders deliver their sugarbeets to a designated receiving stations located throughout the growing area. Sugarbeets are harvested with two primary pieces of equipment. The defoliator removes the green leaves and slices a slab from the top of the sugarbeet root. This removed slab is the growing point of the sugarbeet and contains high levels of impurities, which impede the factory’s ability to extract the sugar from the remainder of the harvested root. The sugarbeet root is then harvested by lifting it from the soil. The sugarbeet harvester also separates some soil and conveys the sugarbeet into a truck to be transported to a receiving station.
Trucks hauling sugarbeets to receiving stations are weighed and off-loaded on sugarbeet pilers. These machines also screen soil from the sugarbeets and pile the sugarbeets in large storage piles, which are 18 to 30 feet tall and 1500 feet long.
Samples of sugarbeets are taken upon delivery to be analyzed for sugar content, purity and tare. Later, sugarbeets are reloaded into re-haul trucks, which deliver the stored sugarbeets to the factory for processing. Large front-end loaders load belly dump trailers which haul 32 tons per load. Piles are monitored for temperature during the storage term. Some piles are forced air ventilated to enhance storage conditions and allow sugarbeets to be stored for longer periods. Harvest is concluded in late October. Sugarbeets can be stored in piles as long as the end of April when the slicing operations will be completed. Then, it is time to begin the process all over again.
Handling sugarbeets
When the beets in storage are transferred from the storage pile with a loader into a re-haul truck, they are delivered to the factory’s receiving hopper. The beets are then conveyed to the factory’s washing and cleaning station via an underground conveyor belt system. Since the sugarbeet has a nearly identical density to that of water, their transport inside the cleaning station is made much easier by being carried in a current of water, called a flume. The beets then enter a series of two beet washers to remove large dirt clumps in large tumbling drums partially filled with water, then on to a series of two rotary rock catchers, all of which to remove anything that could dull the slicing knifes. A large screw conveyor extracts the beets from the water and onto an elevated final spray wash table, before being conveyed (by a series of belts) to hoppers above the beet slicers.
Extraction of sugar by diffusion
After cleaning, the next step in the “extracting” process is slicing. In order to extract the soluble materials from the insoluble materials in the sugarbeet, a maximal amount of the surface area must be exposed to the hot water extracting solution. The sugarbeets are sliced into thin rectangular strips called “cossettes”, which resemble shoestring potatoes. This is done in large drum slicers, a type of industrial grater, set with several pairs of rotating opposed groove knives.
Slicing beets into cossettes
The cossettes are then conveyed across a weightometer, which feeds back information that controls the rate of slicer activity, and into the cossette mixer. Here the cossettes are scalded with hot juice to break down the cell walls in preparation for extraction of the juice, and then pumped to two diffusers. Hot water is introduced at one end of the diffusers and the cossettes at the other. The cossettes are propelled upward by a large, vertical screw conveyor.
Diffusers
As the cossettes continuously come in contact with hot water containing a lower sugar content, more and more soluble sugar and other compounds are extracted from the cossettes. By the time the hot water leaves the diffuser, after passing by all the cossettes, the cossettes are essentially depleted of all of their sugar and other soluble materials which is now in the water, now referred to as “raw juice”.
Carbonation / clarification and filtering of the juice
The next major step is to separate approximately 40 percent of the soluble non-sugar materials produced by the sugarbeets, which were extracted along with the sugar in the diffuser, from the high sugar content raw juice. This involves heating the juice and adding various compounds like calcium hydroxide and carbon dioxide bubbles. The non-sugar materials are then removed with a settling process. More carbon dioxide bubbles are added to further remove non-sugar components. The juice is then heated again and the unwanted components are filtered out. The remaining juice has sulfur dioxide gas added to prevent browning during additional heating steps. The juice at this stage in the process is now called thin juice.
Evaporation
The thin juice flows to a surge vessel and pumped through a series of multiple effect evaporators. The thin juice enters the evaporator set at about 12 to 18 percent solids and leaves between 61 and 72 percent solids. The juice at this stage is called thick juice. Sugar from a second crystallization step is added to the thick juice, then additional evaporators remove more water from the juice so that eventually they reach at least 72 percent to form a syrup or “standard liquor” which is ready for crystallization.
Crystallization
The most important step in the separation process is that of crystallization. It is more than 99 percent effective as a purification step and without its use, further separations would have to be made in order to purify the sugar acceptably for commerce today.
Crystallization takes place in specially designed vessels called “pans”. Each pan of sugar boiled is called a “strike”. Standard liquor is introduced into the pan to a level known as the charge level. It is then boiled under vacuum, while continuously adding more standard liquor feed to maintain the charge level, until it reaches a concentration where no further sugar would dissolve in the syrup if it were added. This point is known as the “saturation point”.
The pan is then carefully raised in concentration above the saturation point to a preset “supersaturation point”. Then a pre-measured quantity of very fine milled sugar crystals are added as a seed on which the sugar will deposit and become macroscopic crystals. The standard liquor feed is then increased to maintain crystal growth. When the pan is nearly full, the feed is stopped. Then, the percent solids of the mixture of sugar crystals and syrup in the pan is raised to about 92 percent by evaporation. A great deal of crystal growth occurs during this “brixing-up” process.
Centrifuges separate massecuite from syrup
At this point the mixture of crystals and syrup from which the crystals have been grown is called “white massecuite” or white “fill-mass”. The pan is now “dropped”, which means that vacuum on the pan is released, and the massecuite allowed to flow by gravity to a mixer above the white centrifugals. The mixer keeps the massecuite in suspension until the syrup can be separated from the crystals by centrifugation. Centrifugals are large electrically driven machines with baskets or “tubs” enclosed within. The baskets are then spun at high speeds. The result is that the syrup is spun out through holes in the screen and the sugar crystals are trapped on the face of the screen. The sugar crystals are then washed with hot water and/or steam. The syrup and crystal washings are collected and returned for further crystallization and the sugar is removed from the screen either mechanically or centrifugally, dependant upon machine design.
Molasses is one of the three final end products of the factory. It contains about 60 percent of the soluble non-sugars originally extracted with the beet and its sucrose content approaches 50 percent. The non-sugars concentration, however, prevents further crystallization within reasonable time limits.
Sugar crystals must be dried and cooled prior to storage
White sugars, after purging and washing in the centrifugals, are conveyed to the “granulator” for drying and cooling. The granulator is a long rotating cylindrical device, which forces the sugar crystals to tumble through a continuous draft of hot (drying) or cold (cooling) air.
Following their passage through the granulator the sugar is first weighed (for accounting purposes) then conveyed, through a silo distribution system. The sugar must remain in the sugar silos to cure for a minimum of 48 hours prior to packaging or shipping.
The amount of sugar produced from sugarbeets ranges from 70 to 86 percent of the sugar that was in the beets when processed. The wide range is due to the quantity and nature of the non-sugars that were also contained in the beets, along with factory processing techniques.
Mark your Calendars
• Have cold temperatures or life in general been stressing you out? Hammer out your frustrations with us at McCrory Garden’s Wine & Madness event! This workshop will show you how the dye from plants can be transferred to fabric, making a beautiful art piece. Wine, beer, and soda will be available, and your first glass and a light snack is included! Is your holiday Poinsettia losing its beauty? Bring it along and make it into a lasting art piece! Supplies will be provided, but you may bring your own hammer, dish towel, or flowers if preferred! The workshop is held at the McCrory Gardens Education & Visitor Center, 631 22nd Ave., Brookings, SD, Jan. 26, from 6:30 – 8 p.m. Workshop is $20 per person and is limited to 20 participants! Please register for this event by calling the welcome desk at (605) 688-6707, or go visit our website at www.McCroryGardens.com.
• Spring Fever 2018 Gardening Event will be held in the Rushmore Room at Ramkota Hotel in Rapid City on March 3, from 8 a.m. – 4 p.m. This year’s conference features two presentations by Dr. Linda Chalker-Scott of Washington State University, speaking on “Evidence Based Gardening Information” and “The Root of the Problem, When Plants Don’t Thrive”. Dr. John Ball, SDSU Professor and Extension Forestry Specialist will present “Selecting Trees for Western South Dakota.” Short “table talks” topics include: “Growing Vegetables in Containers on Your Deck or Patio”, “Caring for House Plants”, “Conserving Water in Your Garden”, and “Using Compost and Mulch in Your Garden”. Lunch catered by Minerva’s is included in the $35 registration fee. The event includes a Silent Auction, Door Prizes and a Free Table. Registration limited to 200, please register before Feb. 27. Visit www.blackhillsgarden.com under the “Welcome” tab for registration blanks and more information.
