I use ROE in oils to help ward off rancidity of the oils. In conjunction with EDTA (ethylene-diamine-tetra-acetic acid) to ward off DOS. PLUS the EDTA helps reduce soap scum. The combo works very well for me.
Here is a good article on what ROE (Rosemary Olesresin Extract) is and why it is often used in and by soapmakers:
Classic Bells restores antique sleigh bells and manufactures bell home decor. Wholesale. Retail.
classicbells.com
Here is a good reference that is written by
Dr Kevin Dunn (chemistry professor & author of Scientific Soapmaking) that documents scientific results of different additives used in soap for the purpose of warding off DOS:
As many other soapers have reported doing, I add it to each container of liquid oil when I open it (and write the date the ROE was added onto the container so I know for sure it was done.) I also sometimes add it to hard oils after melting to use in soap, paricularly if the formula doesn't contain a lot of soft oils.
And another good article on EDTA (just as an FYI):
Classic Bells restores antique sleigh bells and manufactures bell home decor. Wholesale. Retail.
classicbells.com