Why Butter Goes Rancid or Mouldy — And How Adele Macer Ceramics Butter Bells Keep It Fresh

🧈 Why has my Butter Gone Rancid?

Rancidity is a form of spoilage that happens when fats oxidise — meaning they react with oxygen in the air. Butter is about 80% fat, and when those fat molecules break down (especially unsaturated ones), they form free radicals and peroxides, which give off that sharp, sour, "off" smell and taste.

Things that speed up rancidity:

• Air (oxygen exposure)  
• Heat   
• Light
• Time  

This is why leaving butter out uncovered in a warm kitchen or in direct sunlight will shorten its shelf life.

 🍄 Why has my Butter Gone Mouldy?

Mould is caused by airborne spores landing on butter and growing in the right conditions — particularly when moisture and warmth are present.  

Even though butter is mostly fat, it still contains a bit of water and milk solids (like proteins and sugars) that mould *loves*. If it's exposed to air, especially humid air, those spores can start multiplying.

 💧 How will a Butter Bell Help?

A butter bell slows both processes down by:

- Sealing the butter off from air using a layer of cool water  

- Blocking light (especially with opaque ceramic styles like mine)  

- Keeping a stable temperature on the bench — cooler and less fluctuating than being opened and closed in a fridge  

- Reducing moisture loss and exposure, which helps maintain texture and freshness  

👉 As long as the water is changed every 1–2 days, and the butter isn’t kept near a hot stove or in high humidity, it can stay fresh and safe to eat for up to two weeks.

More FAQ here

References:

1. Healthline: Does Butter Go Bad If You Don't Refrigerate It? - Healthline+1The Kitchn+1

2. University of Minnesota: Field Studies of the Sources of Mold in Butter - University Digital Conservancy

3. Food Network: Is It Safe to Leave Butter on the Counter? - Food Network

4. America's Test Kitchen: Butter Bell Storage