Milk sours when microorganisms convert lactose into lactic acid.
Acidity
As acidity rises, milk proteins lose stability and begin to thicken or form curds.
Temperature
Warmth speeds microbial growth, but uncontrolled warmth can also encourage unwanted organisms.
Controlled culture
Modern cultured dairy products use known starter cultures and sanitation to make the process more predictable.
Frequently asked questions
What is bonnyclabber?
Traditional sour or curdled milk.
Where does the name come from?
It is generally linked to Irish Gaelic bainne clabair, meaning thickened milk.
Is bonnyclabber the same as yogurt?
No. Yogurt uses specific cultures and controlled warm incubation.
Can I make it from raw milk?
Traditional methods did, but uncontrolled raw-milk fermentation can carry food-safety risks.
What is the safest modern approach?
Use pasteurized milk, clean equipment, and a reputable cultured starter.
Can buttermilk replace clabber?
Yes, especially in baking.
Was it eaten in Appalachia?
Yes. The food and word are associated with Scotch-Irish and Appalachian foodways.
Is sour milk always safe?
No. Sour odor or curdling alone does not prove safety.