Sugar Lime and Calcium Oxide

What is sugar (beet) lime, how is it made, and why is it prohibited for use in USDA organic crop production?

Beet sugar refineries typically operate on-site limekilns that burn limestone to produce calcium oxide—also known as burned lime or quick lime. In addition to calcium oxide, carbon dioxide is also produced. Both calcium oxide and carbon dioxide are used in sugar refining processes, and the chemical reaction can be written as follows:

CaCO₃ + heat → CaO  + CO₂

Cane sugar refining also uses quicklime but at a lower rate. In both cases, calcium oxide and carbon dioxide are used to “clarify” the juices. Clarification is essentially a purification step that aims to remove as many non-sugar components as possible from the raw sugar juice. Depending on their identities, these non-sugar components will flocculate (clump together), neutralize, and eventually precipitate out from the raw sugar juice. 

In beet sugar production, lime is used at a ratio of 0.25 ton per ton of sugar. Since calcium oxide rapidly hydrates to calcium hydroxide, and also in presence of air and carbon dioxide will re-carbonate. The final post-clarification waste lime product mixture is in fact a calcium carbonate—chemically identical to limestone—rated at 80-90% calcium carbonate equivalent, mixed with 4–10% organic matter. While calcium hydroxide is approved as a nonorganic processing aid, it has not been approved as a crop material.  

Burning of minerals, which accomplishes a chemical change in the structure of the chemical, has been considered a synthetic process by the NOSB since 1995. Because the substance is synthetic and not on the National List, sugar lime is prohibited in USDA organic production.

This article was originally published in the spring 2003 issue of the OMRI Materials Review newsletter, and was updated in April 2023 by Technical Director Doug Currier.