DOS ? on my original first batch of soap?

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"... dos is primarily an issue of oxidised (rancid) oils used in the soap making...."

Rancidity and oxidation are two different things. A fat can be rancid or oxidized or both. Oxidation is the breakdown of fat into diglycerides, monoglycerides, fatty acids, and glycerin. Rancidity is the breakdown of fats and fatty acids into ketones and aldehydes, which are the chemicals that give rancid fat that distinctive "off" odor. See the difference?

Further, the issue of rancidity in soap is not quite so cut and dried. Using rancid fats certainly leads to soap that is rancid, but you can get rancidity in soap even if you use fats that test perfectly fresh.

Spots of rancidity (DOS), such as Loriag is seeing, come from discrete contaminants, most likely metals that come from harvesting and processing machinery, soaping equipment, the air or one's hands, etc.

Overall rancidity can be created by rancid fat, but it can also be triggered by other ingredients that are mixed throughout the soap. Examples include oxidized essential oils (older lavender EO being a prime example), or metals in tap water, or additives that supply metal ions; chlorophyll being one culprit.

You can do your best to minimize the chance of overall rancidity or DOS, but you can never entirely eliminate the possibility. You can also use additives to combat oxidation and rancidity if and when it happens. These include chelants, such as tetrasodium EDTA and citrate, and antioxidants, such as rosemary oleoresin (ROE). Pairing a chelant with an antioxidant is a good way to go -- EDTA pairs well with ROE, for example.
 
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I live in a Nortern Canadian town. We are about 5000 people but kinda end of the road for the grocery delivery. I have been buying my OO in 1 L bottles to always use fresher oil as a I would go through it faster.
Climate is cold, we still have snow. The house remains at a constant warmer temp but the room my soaps are in is a bit warmer. I guess with windows and doors shut it could get humid at times if I’m cooking a lot. I have a cealing fan that gets turned on in the drying room.
My molds are silicone, my drying wrack should be stainless steal for dishes. I do use one of the silicones repeatedly.
DOS was first found with just two bars with two spots. Than I found some on a whole batch with a fair amount in the bottoms and edges. Than another batch an the bottoms. Possibly one more now that I am searching desperately for it, the spots if they were were so light it was hard to be sure.
I have the bars sitting on paper towel in plasticcontainers no lids on to dry and I turn them often.
 
Go scrub the heck out of your silicone molds! Use hot water, dawn, and a splash of vinegar in the rinse. Take them into good light and check the edges/corners for a shiny yellowly look-if found, scrub again. Use a toothbrush/chewed toothpick to get the corners. I narrowed my issues down partially to a film left behind on silicone molds (from bad oils) in my dos fight....you may have something similar going on.

Also, what FO did you use? Was it all different FOs that dos'd or just one particular one? And how old was it?
 
Go scrub the heck out of your silicone molds! Use hot water, dawn, and a splash of vinegar in the rinse. Take them into good light and check the edges/corners for a shiny yellowly look-if found, scrub again. Use a toothbrush/chewed toothpick to get the corners. I narrowed my issues down partially to a film left behind on silicone molds (from bad oils) in my dos fight....you may have something similar going on.

Also, what FO did you use? Was it all different FOs that dos'd or just one particular one? And how old was it?
This is great advice. Then after that, bake them in the over for an hour at 350F to drive off any volatiles.
 
Ah, that's super good advice about keeping molds really clean -- I will have to add it to my tips for preventing DOS.

I use wood molds that are lined with freezer paper. Since I never reuse the paper, the issue of residue in the molds never occurred to me.
 
All my FO were purchased Feb. and March. Everything is new as I just started soaping Jan. 31.
 
Don’t use steel drying racks. Cheap stainless steel is not good protection. Don’t use plastic containers to cure your soap. You need air flow. Use plastic or timber racks so the air can flow around the bars freely. For long term storage (castile) after 3 months curing put them in cardboard boxes with holes.

Check the temperature of your curing room. It might be better if it is unheard.,
 
Go scrub the heck out of your silicone molds! Use hot water, dawn, and a splash of vinegar in the rinse. Take them into good light and check the edges/corners for a shiny yellowly look-if found, scrub again. Use a toothbrush/chewed toothpick to get the corners. I narrowed my issues down partially to a film left behind on silicone molds (from bad oils) in my dos fight....you may have something similar going on.

Also, what FO did you use? Was it all different FOs that dos'd or just one particular one? And how old was it?
Do you still use silicone? Do you now line them for extra precautions? I’ll definitely be scrubbing the heck out of them.
 
I use silicone molds, wash them in hot soapy water and let them soak. I cure all my soap on metal racks lined with needlepoint plastic. Never had an issue. When cured, I store them in cardboard baseball card boxes.
 
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The only metal is my dish rack for drying dishes. The soap hasn't come into contact with it. But the molds and of course any spoons, and container used. Time to super wash all my stuff. My order with the EDTA should arrive by Friday.
 
I use silicone molds bit wash them in hot soapy water and let them soak. I cure all my soap on metal racks lined with needlepoint plastic. Never had an issue. When cured, I store them in cardboard baseball card boxes.

Yes, sorry. I thought loriag was saying she dried her soap on the steel dish rack.
Then put them in plastic containers.
 
Do you still use silicone? Do you now line them for extra precautions? I’ll definitely be scrubbing the heck out of them.
Yep, and just ordered some more. But I'm not bothering to line them. I am however washing them twice and including vinegar in the rinse water!
 
Based on what people say who have used both, it looks like EDTA is more effective than citrate for controlling DOS and soap scum. It has a bit of an PR problem with the "natural" crowd, so if that is a concern, you'll want to use citrate instead.

I haven't compared the two, so I can't say from personal experience. I have had very good results using EDTA at 0.5% (5 grams EDTA powder per 1000 grams of fat).

I make a 50% solution of EDTA in water and use it that way because it's easier to measure. If you go this direction, the dosage would be 10 grams of EDTA 50% solution per 1000 grams of fat.

I am just a wee bit confused so please correct me if I am wrong- my oil weight is usually 360 g.
I would need to use 3.6 g of 50% solution per 360 g of oils.
So I don't use total batch weight, just oil weight, and I don't enclude EO or FO weight into any weights at all.

Edited to add or

My total batch weight is 531 g. Not including FO or EO
I would need 5.3 g of 50% solution per 531 g of total batch weight.
 
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