Not being a chemist, I can't say for sure. But below is what I had written in a previous post. Perhaps a more knowledgeable member can chime in.is it the tallow causing it for to rancid? I have plenty of other tallow soaps and none have gone rancid on me. I think someone said it was the almond oil in cella that makes the soap go rancid. maybe some others can verify this.
I had a tub of TSE shaving soap that lists tallow as the main ingredient, go bad in a little over 3 months. My tub of Cella red is kept in the fridge just in case. I also have a tub of Cella green which doesn't contain tallow, that sets out on a shelf.