Rancidity

The one failure in this category that is a genuine quality problem rather than a cosmetic one.

The customer tastes it

Crayon, old nuts, putty, paint. A rancid balm smells wrong before it tastes wrong, and on a lip product the customer gets both.

It is also unrecoverable and it arrives as a complaint about a product that was fine when it shipped.

What is actually happening

Oxidation of unsaturated fats. Oxygen, warmth and light drive it; the more unsaturated the oil the faster it goes.

A lip balm lives in a pocket at body temperature for months, which is close to the worst storage condition available. The product design works against you here in a way it does not for a jar on a shelf.

There is no microbial component. An anhydrous balm has no water for anything to grow in, which is why it needs no preservative, and why an antioxidant is not one.

Slowing it down

Choose stable oils: jojoba, fractionated coconut, castor. Use the delicate ones for character rather than as the base.

Buy small and fresh, and ask for the pressing date rather than the best-before.

Store stock cold, dark and sealed, and decant working quantities.

Add vitamin E, understanding what it is: an antioxidant that slows the reaction, not a preservative and not a reset.

What it means for your dating

The finished product is only as long-lived as its shortest-lived ingredient, measured from that ingredient's production date rather than from your pour date.

Which is the argument for a period-after-opening or a best-before that reflects the formula rather than a round number, and for not building twelve months of finished stock in one run.

References