Flotation Aids

How are floating agents used, and which materials are allowed?

By Ana Negrete

Post-harvest production practices include cleaning, sorting and storing produce in order to preserve its freshness and quality, while maintaining its essential form. Among these practices is the use of water-based unloading of field bins. This practice helps reduce produce injury/bruising, and also helps transport free-floating produce through the processing line. Unfortunately, not all crops tolerate wetting, and those that do don’t necessarily float in water. 

Although not much can be done regarding water tolerance for produce, floating agents can be used to make produce float. Floating agents include salts added to the water to increase its density, allowing produce to float that would otherwise sink. 

In January 2016, the National Organic Program (NOP) published Guidance 5023 that addresses the substances allowed for use in post-harvest handling of organic products. Per this Guidance, there are three possible options for allowed flotation aids:

1. “Synthetic substances that are listed in §205.601 of the National List specifically for post-harvest…” Only sodium silicate is listed in this section of the regulation for post-harvest use. Furthermore, sodium silicate is only allowed as a flotation agent for tree fruit, and for fiber processing.
   
   
2. “Substances listed in §205.605 of the National List may be used for post-harvest handling…” This option is contingent on there not being a restriction limiting the use of the substance.  Salts that meet these criteria include sodium carbonate and potassium carbonate.
   
   
3. “Natural (nonsynthetic) substances allowed for use in crop production that are not restricted or prohibited in §205.602 of the National List…” Sodium sulfate may comply with this section of the Guidance, provided that it is from a natural (nonsynthetic) source.

The National Organic Standards Board (NOSB) received a petition to remove lignin sulfonate at §205.601(l)(1) for use as a flotation aid. The petition noted that there are other alternatives to the use of lignin sulfonate (some of them noted above), and the material is not commonly used. As a result, the NOSB voted in 2015 in favor of removing lignin sulfonate from the National List as a floating agent. This recommendation to remove lignin sulfonate for this purpose was implemented by the NOP in 2017.

This article was originally published in the summer 2017 edition of the OMRI Materials Review newsletter. It was reviewed and updated in October 2019 by Senior Technical Coordinator Peter Bungum.