Detecting Starch in Milk: The Iodine Test


Milk is a widely consumed beverage known for its nutritional value. However, its quality can be compromised by adulteration or unintentional contamination. One common adulterant found in milk is starch, which is added to increase volume or viscosity. Detecting starch in milk is crucial to ensure its purity and prevent fraudulent practices. The iodine test is a reliable and widely used method for the detection of starch in milk. In this article, we will explore the iodine test and its significance in identifying starch contamination in milk.

Understanding the Iodine Test:

The iodine test is based on the reaction between starch and iodine, resulting in the formation of a characteristic colour. Iodine molecules fit into the helical structure of starch, forming a starch-iodine complex that produces a blue-black colour. This colour change provides a visible indication of the presence of starch in a sample.

Procedure for the Iodine Test:

Performing the iodine test to detect starch in milk involves the following steps:

  1. Sample Preparation: Obtain a representative sample of milk. Ensure that the sample is well-mixed to ensure uniformity.
  2. Addition of Iodine Solution: In a test tube or a small container, take a small amount of the milk sample. Add a few drops of iodine solution to the milk. The iodine solution is usually prepared by dissolving iodine crystals in an aqueous solution of potassium iodide.
  3. Observation: Observe the colour change in the milk sample after the addition of the iodine solution. If starch is present in the milk, the mixture will turn to a blue-black colour. A lack of colour change indicates the absence of starch.

Significance of the Iodine Test in Milk Analysis:

The iodine test is an essential tool for milk analysis, offering several advantages:

  1. Identification of Adulteration: The presence of starch in milk is considered adulteration, as it is added to increase the volume or thickness of milk, deceiving consumers. By employing the iodine test, milk producers and regulatory authorities can identify such fraudulent practices, ensuring that consumers receive unadulterated and high-quality milk products.
  2. Assessment of Processing Practices: The iodine test can also provide insights into the milk processing practices employed by manufacturers. Any presence of starch in milk suggests inadequate processing or improper handling, which may compromise the quality and safety of the product. Regular testing using the iodine method helps dairy producers monitor their production processes and maintain high standards of milk quality.
  3. Consumer Trust and Safety: The iodine test acts as a quality control measure, promoting consumer confidence in the milk they consume. By conducting regular tests to detect starch, milk producers demonstrate their commitment to delivering pure and authentic products, safeguarding consumer health and trust.


The iodine test is a reliable and widely used method for detecting the presence of starch in milk. By employing this test, milk producers can identify adulteration, assess processing practices, and ensure the delivery of high-quality and unadulterated products to consumers. Regular monitoring using the iodine test helps maintain consumer trust, promote food safety, and uphold the integrity of the dairy industry.