Rosemary oleoresin (ROE)
What does it do? Rosemary OleoResin (ROE) is an antioxidant. An antioxidant will lengthen the shelf life of a fat by preventing the fat from reacting with oxygen, whether the fat is mixed into your soap or lotion or stored in your soaping pantry. An antioxidant is a chemical that oxidizes (reacts with oxygen) more easily than the fat, so it "sacrifices" itself first and thus protects the fat.
ROE is a dark, thick liquid with a distinct "herby" odor in the bottle. It can be added directly to fats or added to soaps and other bath and beauty products that contain fats. If you add ROE to lotions, salves, balms, scrubs, etc., use with a very light hand because the odor may be detectable in these products. ROE is so diluted in soap, you will not be able to smell it.
Can I use Rosemary EO rather than ROE? Until further research proves otherwise, the answer is no. Some people speculate that rosemary essential oil (EO) has preservative properties, but it is unknown whether rosemary EO is as effective as ROE is for preserving fats. Kevin Dunn, author of the book Scientific Soapmaking, has stated that rosemarinic acid that is the key antioxidant in ROE. This acid is not present in rosemary EO.
Even though the EO and ROE are made from the same plant, they contain quite different blends of chemicals due to the way each is made. Rosemary EO is made by steam distillation. Steam distillation removes only the very lightest of the volatile chemicals in the plant material -- the chemicals we call essential oils.
Rosemary oleoresin is made by soaking the same plant material in a solvent. The solvent dissolves the essential oils AND the less volatile chemicals in the plant material. The solvent is evaporated leaving the "oleoresin" behind. An oleoresin contains the EO mixed with the heavier resins, waxes, and oils also dissolved by the solvent.
What kind of ROE to use? ROE is usually sold in varying strengths as measured by its carnosic acid content which can range from 2% to 7%. I have yet to find any supplier that provides the rosemarinic acid content, unfortunately.
I recommend purchasing ROE with 5% to 7% carnosic acid for use in soap.
If you plan to use ROE in other products, you may want to purchase a less concentrated product for ease of weighing and measuring. Another option is to purchase a higher-strength ROE and dilute a portion with a mild oil, such as sunflower oil. Use this diluted ROE in your non-soap products.
A few US suppliers of ROE are Lotioncrafter (7% strength), Wholesale Supplies Plus (7%), Majestic Mountain Sage (2% and 5%).
What if I can only find Rosemary Seed Extract, not ROE? An alternate common name for Rosemary Oleoresin is Rosemary Seed Extract. Since ROE is an extract of the leaves, this alternate name is confusing.
The key is to look at the INCI (official) name -- Rosemarinus officinalis (Rosemary) Leaf Extract (and) Helianthus annuus (Sunflower) Seed Oil. (Note -- The oil and the extract may be in reverse order or the oil may be omitted, depending on the supplier.)
How much should I use? I suggest 0.4 to 0.5 grams ROE per 1000 grams of fat (0.04% to 0.05% ppo) to help preserve fats in storage.
The dosage range is 0.2 to 1.0 g ROE per 1000 g fat (0.02% to 0.1% ppo).
These numbers are based on a ROE with 5% to 7% carnosic acid. If the carnosic acid content in your ROE is lower than that, then adjust the dosage accordingly.
Kevin Dunn recommends 1.0 g ROE for every 1000 g oils (0.1% ppo) to be added when making soap. He found it to be an effective "natural" treatment for rancidity (DOS, dreaded orange spots) in soap. He suggests an even more effective but less "crunchy" combination of 1.0 g ROE and 0.5 g tetrasodium EDTA powder for every 1000 g oils.
Do not use more ROE than necessary -- too much antioxidant can actually accelerate oxidation of fats, a process called "pro-oxidation."
How should I use it?
Stored fats: Add ROE to your fats after you buy them to protect against rancidity right from the start. This is especially important for oils with short shelf lives, such as grapeseed and hemp, but ROE can be added to any fat to protect it during storage. If you render your own lard and tallow, stir the ROE into the warm liquid fat right after rendering.
Since ROE is a thick syrup, it will not mix in easily if you just put the ROE directly into a large container of room temperature fat. A better way is to pour out a little (100-200 mL) of the fat into a cup, mix the ROE into that fat until you can't see any trace of the ROE syrup, add this mixture to the large container of oil, and shake or stir well.
Soap: Stir the ROE into the fats before adding your lye solution.
When making soap with fats treated with ROE, you may notice the soap batter briefly turns bright orange right after the lye solution is mixed into the fats. In my experience, this blush of color fades away after several minutes, and the finished soap is not discolored.
How much lye does it neutralize? None! Do not adjust your lye weight for ROE.