Rancidity is one of the most common quality issues in butter, leading to undesirable flavours, odours, and a shortened shelf-life. It occurs when fats break down into smaller compounds such as free fatty acids, aldehydes, and ketones - substances responsible for the off-flavours described as "soapy", "painty", and "oxidised". Managing rancidity requires understanding its causes and implementing effective preventative and corrective measures.

This form of rancidity occurs when lipase enzymes or microbial contamination cause the breakdown of milk fat into free fatty acids, particularly butyric acid. It often results from:

* Poor cream pasteurisation or microbial contamination (e.g., psychrotrophic bacteria).

* Improper washing of butter granules, allowing residual buttermilk to remain.

* Inadequate temperature control during churning or storage.

This occurs when unsaturated fatty acids react with oxygen, forming peroxides and aldehydes that cause a tallowy or metallic flavour. It can be accelerated by:

* Exposure to air, light, or high temperature.

* Presence of metal ions (iron, copper) from equipment or water.

* Insufficient antioxidants or loss of natural protective components such as carotenoids and tocopherols.

Use high-quality cream from fresh, well-handled milk with low bacterial counts. Avoid prolonged storage of raw cream at high temperatures.

Pasteurisation destroys lipase-producing microorganisms that trigger hydrolytic rancidity. Proper time-temperature control is essential.

3. Oxygen and Light Management
Store butter in airtight, opaque packaging to limit oxygen exposure and light-induced oxidation. Use inert gas flushing where possible.

Regularly inspect stainless steel surfaces and avoid copper or iron contact. Prevent residue buildup and water contamination in churns and pipelines.

Store butter at low temperatures (ideally below 5 ºC) to slow both enzymatic and oxidative reactions.

Natural antioxidants like tocopherols or ascorbic acid can be used to delay oxidation and extend shelf-life.

When rancidity is detected:

* Identify the type (hydrolytic vs oxidative) through sensory evaluation and chemical testing (e.g., peroxide value, acid value, free fatty acid analysis).

* Trace the source - check cream quality, storage temperatures, microbial counts, and potential contact with metals or air leaks.

* Corrective actions include equipment cleaning, adjusting storage conditions, and retraining personnel on handling practices.

Routine monitoring and preventive maintenance should be part of every butter plant's quality assurance program.

Rancidity in butter not only impacts flavour and consumer acceptance but also signals potential lapses in processing or storage control. By understanding its causes and maintaining strict hygiene, temperature, and oxygen control, manufacturers can produce butter that retains freshness, natural aroma, and nutritional value through its intended shelf-life.

* "Butter - Transport Information Service" (TIS-GDV)

* "Best Practices for Storing Butter" (Agriculture Notes)

* "Butter Science 101" (Centre for Dairy Research)