Sweet Sorghum

December 5, 2006


It seems that every time there is an energy crunch, Vincent gets involved with a sweet sorghum project. The attraction is two-fold: sorghum is very easy to grow, and sorghum contains a high level of sugar.

Other plants, like corn, sugar beets, sugar cane, vegetables, and all fruits, also contain sugar. All of these can be used as part of ethanol, biogas, and other bioenergy schemes. So it is no surprise that, with this year's high energy costs, Vincent currently has projects underway involving sorghum, corn, beets, cane, banana, oranges, and onions.

This year's sorghum project involved testing a variety of Florida sorghums. The juice yield, along with the amount of dissolved sugar (Brix*), was measured. The effect of shredding, or not shredding, was studied. The benefit of using a Vincent Twin Screw press as a combination shredder and press was also evaluated.

Sorghum is a soft cane-like plant. It is fibrous, but not fibrous enough to cause problems with shredding or abrasive wear. This gives it an advantage over sugar cane. It is a little like water reeds, only thicker (3/4" diameter) and taller (8').

Most of the sorghums tested measured only 7º to 9º Brix. This was presumed to be lower than normal because of the maturity of the plants. The juice yields ranged from 66% to 79%. The project was focused on providing a sugar solution that could be used in the production of ethanol at Bartow Ethanol.

These sorghums, as harvested, measured 81% to 83% moisture content. The press cake ranged from 45% to 59% moisture content.

A search of our files revealed interesting reports and articles, all based on testing with Vincent screw presses:

    • 1992 Savant-Vincent measured 15.2 Bx, 57% juice yield, 54% press cake moisture.
    • 1985 ASME report measured 67% to 70% yield on chopped sorghum; 54% to 57% juice yield on crushed sorghum. Press cake moisture content was 58% to 52% and 62% to 60%, respectively. The liquid may have been 11 Bx.
    • 1983 Biomass Workshop reported 72% moisture in the as received samples, 57% juice yield. Brix may have been 14 Bx.

Overall, these projects were technical successes in that they demonstrate that sorghum yields high Brix juice that is suitable for the production of ethanol. However, the projects all fail commercially because the price of fuel oil is not high enough for the projects to be justified. Nevertheless, it is comforting to know that alternative, renewable energy sources exist, should the day come when the availability of fossil fuels declines.

*Brix Definition: Dissolved solids divided by the sum of the dissolved solids plus water, multiplied by 100. Note that suspended solids do not enter into the equation.

Issue 181