Does de-heading sweet sorghum increase syrup yields?

Authors: Knoll, Joseph

Submitted to: Popular Publication
Publication Type: Other
Publication Acceptance Date: 5/7/2025
Publication Date: 5/7/2025
Citation: Knoll, J.E. 2025. Does de-heading sweet sorghum increase syrup yields? NSSPPA Newsletter 39(2),6.

Interpretive Summary:

Technical Abstract: Most growers who choose to remove the developing grain heads from their sweet sorghum crop do so to reduce incidence of lodging. This is particularly important for mechanized harvesting, as even partially lodged cane can be difficult or impossible to collect with mechanical harvesters. Lodged cane also tends to collect more dirt, which must be filtered out of the juice. Another perceived benefit of ‘de-heading’ or ‘topping’ is an increase in sugar accumulation in the stem, which should lead to greater syrup yields. The theory behind increasing sugar production by removing the grain head has to do with ‘source–sink’ relationships in the plant. Sugars are produced by photosynthesis in the leaves (source) and are moved via the phloem to growing parts of the plant including buds, roots, developing grain heads, and storage cells in the pith of the stem (sinks). Removing the grain head eliminates a very strong sink, thus redirecting the sugars to the stem. So, two questions are: 1) how large is this effect on sugar (or syrup) yields and 2) is there an ‘optimum’ time to de-head your sorghum. Back in 1973, Dr. Dempsey Broadhead of the USDA-ARS attempted to answer these questions by de-heading Rio sweet sorghum in Mississippi at either boot or flowering stage, and comparing with a non-treated control, repeating the test over three seasons. He observed a slight decrease in juice extraction percentage, which is juice weight divided by stalk weight, (42.2–42.5 %) with de-heading versus control (44 %), but a slight increase in juice brix (19.6–19.7 Bx) with de-heading versus control (18.9 Bx). Overall, the calculated sugar yield per acre was not different among treatments. A more recent study (2012) was conducted by Dr. John Erickson and colleagues at the University of Florida using M81-E sweet sorghum at two locations in North Florida. They also de-headed at boot and flowering and compared to a non-treated control. They found no differences in extraction percentage among treatments, but an increase in juice brix (14.2–14.7 Bx) with de-heading versus control (13.6 Bx), leading to a calculated increase in sugar yield per acre of around 13 % in the de-headed treatments. A study in India in 2000 by Dr. C. Rajendran and colleagues compared de-heading at flowering versus untreated control in ten sweet sorghum varieties. Interestingly, they found a decrease in juice brix with de-heading (18.0 Bx) versus control (19.2 Bx), averaged across the ten varieties. However, stalk yield and juice extraction percentage both increased with de-heading, which resulted in an increase in sugar yield in the de-headed treatment. They noted that the de-headed stalks were slightly thicker than control and had numerous side branches, which could explain this increase. So, to summarize, one study (Mississippi) showed decreased juice extraction, increased brix, and no change in sugar yield with de-heading. Another study (Florida) showed no differences in juice extraction, increased brix, and an increase in sugar yield with de-heading. Lastly, the study from India found increased juice extraction, decreased brix, and an increase in sugar yield with de-heading. So, why the differences? Each study used different varieties of sweet sorghum, and they were conducted in different climates, and these factors could certainly affect the results. Even the type of mill used to crush the cane could have an effect on juice extraction, though only the Florida study gave much detail on milling parameters. A common conclusion that we can draw is that de-heading will typically have no significant effect on total sugar (and thus, syrup) yields or will result in a slight increase. As for optimal time to de-head, the two studies from the U.S. found no major difference between de-heading at the boot stage versus de-heading at flowering.