Sorghum Production: Milling and Cooking

A great natural sweetener, sorghum is unique and delicious. Sorghum production begins with milling, and many cooking techniques can be used to make sorghum syrup. Sorghum production is practiced by farmers and supported by consumers who are looking for a natural self-sustaining sweetener.


| November 6, 2012



Sorghum Syrup

You'll be surprised at how tasty sweet sorghum syrup can be.


Photo by Lara M. Ervin

Covering a modern homesteading tradition in his book, Sweet Sorghum (Lara M. Ervin, 1992), George Kuepper discusses ways to transform this natural sweetener from plant to plate.  Sorghum production is a practice used by many farmers to produce sorghum syrup. Sorghum is a natural sweetener that benefits health, body and food. This excerpt is from Chapter 12 and Chapter 13; it describes milling and cooking methods of sorghum production. Learn more about growing and harvesting sweet sorghum by reading Growing Sorghum: A Natural Sweetener. 

You can purchase this book through Kerr Center Publications: Sweet Sorghum.   

Sorghum Production: Mills

The three-roller mill has become the standard in extracting cane juice. It was invented by Pietro Speciale, the Prefect of Sicily, in 1449. The rollers were fastened vertically, and this type of mill supplied almost all of the world’s sugar for close to 350 years. The design is typified by horse- or mule-driven mills, commonly seen in very small sorghum operations and in traditional demonstrations at festivals and fairs. They are still easily found in the South and Midwest. Many have been adapted to gasoline engines or electric motors. Larger and more modern mills are of a horizontal design but still have three rollers. Power is usually supplied by stationary engines, electric motors, tractor pto, or hydraulics.

Most small- and medium-scale producers purchase and refurbish old mills, although a few have built new ones. The major problems with using old mills are metal fatigue and the difficulty in finding replacement parts. While most foundries have the capability of making them, the cost is often prohibitive. Like row binders, get a second mill for backup, or keep several old mills of the same model for parts. Maintaining a mill requires the same common sense applied to other equipment upkeep. Because bearings work at low speed, lubrication can guarantee a long life if not otherwise abused. Running the mill at a correct feeding rate and speed will make it last longer and decrease downtime. It is important to use only food-grade grease on any portion of the mill where the lubricant might come into contact with either stalks or juice. This includes all roller bearings. Food-grade grease can be bought from most apiary (beekeeper) supply houses and from suppliers to the food industry.

Milling Sorghum

Efficiency of juice extraction is the goal of milling. It is accomplished by proper maintenance of the roller surfaces, accurate spacing of the rollers, correct roller speed, and skilled feeding of the mill. Most rollers on three-roller mills are grooved. The surfaces are neither convex nor concave, so any adjustment is uniform along the length of the rollers' interface. After several seasons of use, the center of a set of rollers may become concave since cane is normally concentrated there during milling. Regrinding and regrooving are required for continued extraction performance. When rollers have been repeatedly ground and can no longer be properly adjusted, they can be sleeved with new metal and lathed to original size. Spacing of rollers on three-roller mills is standard; however, each unit should be checked for imprinted instructions to the contrary. A 3/8 inch gap is needed between feeder and top rollers, and a 1/16 inch gap between the expeller and top rollers. Adjustment bolts are positioned on each end of the smaller rollers and are used to set the gaps.

The current recommended speed for a three-roller mill with a top roller diameter of 12 inches is 7.5 rpm for the top roller. The speed of top rollers on smaller mills is closer to 9 rpm. This contrasts with earlier recommendations that called for top roller speeds of 9 to 11 rpm for large mills and 10 to 12 rpm for small mills (Freeman et a1., 1986). A study in Tennessee found top roller speeds ranging from 4.8 to 11.4 rpm, with most averaging close to 8 rpm (Wilhelm and McCarty, 1985). Trials carried out by farmers have shown that as much as 20 percent of the potential juice yield is lost by increasing mill speeds from 7.5 to 12 rpm (Wilhelm, 1987). One way to check a mill for extraction efficiency is to weigh 100 pounds of stalks, mill them, and weigh the extracted juice. An effective mill will squeeze about 45 to 50 pounds of juice per 100 pounds of cane.  Efficient feeding of the mill requires steady pushing of the stalks, butt end first. Capacity of mills will vary, but maximum capacity should be maintained as much as possible. A properly set and operated mill will expel stalks with joints breaking over as they leave the last roller. Cane waste should be dry to only slightly sticky.





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