How to Identify Pure Milk: 7 Home Tests for Adulteration

Why milk adulteration is a real concern:

Here are some simple tests to identify the purity of milk.

1. Test 1: The Sloping Surface Test

   Dilution of water reduces the nutritional value of fats, proteins, and minerals.

   • Place a drop of milk on a clean, polished, slanted surface (tilted glass or smooth tile).
   • If the drop flows quickly and leaves little or no white trail behind, it likely has excess water. If it stays put or flows slowly, leaving a visible white trail, it’s more likely genuine

   Why it works: Adulterated milk with extra added water is less creamy, and so it spreads faster. Adulterated milk with extra water is less viscous, so it spreads faster.

   Tip: Do this test with the milk at room temperature for consistency.

2. Test 2: Lather / Detergent Test

   Adulterating milk with detergents can irritate your digestive tract and irritate the digestive tract with foaming.

   • Take 5 ml of milk and mix with 5 ml of water in a transparent glass.
   • Shake rapidly and see if it forms a dense, persistent froth or lather; it may have detergent or synthetic foaming agents.
   • If the milk is pure, it will have a thin, quickly-disappearing foam, which is typically seen in pure milk.

   Why it works: Detergent gives stable foam because it lowers surface tension.

   Tip:Do the test in natural light so you can easily judge foam height and persistence.

Read More: Is Your Ghee Pure? 7 Simple Tests to Detect Adulteration at Home

3. Test 3: Iodine / Starch Test

   Additives like urea, starch, and neutralisers alter the chemical profile of milk and can lead to kidney/bowel issues in vulnerable people.

   • Boil 2-3 ml of milk with 5 ml of water and let it cool down, adding 2-3 drops of tincture of iodine.
   • If the color, it may have starch (added via flour, potato, etc.), and if the colour stays unchanged or faintly yellowish, it's likely free of starch adulteration.

   Why it works: Iodine reacts with starch to form a blue complex.

   Tip:You can skip the boiling step if you just want a quick check, but boiling gives more reliable results.

4. Test 4: Urea / Ammonia Check (Litmus Paper)

   • To check for urea or ammonia, mix 5 mL of milk with 5 mL of water in a test tube and add a red litmus paper.
   • If the litmus paper turns blue, it may have urea or ammonia-based additives.

   Why it works: Urea or ammonia raises the pH of milk, making the environment more alkaline.

   Tip:Keep litmus papers handy in your kitchen kit; they’re inexpensive.

5. Test 5: Formalin / Preservative Check

   Preservatives like formalin/hydrogen peroxide are added to keep the milk looking fresh - they are strictly illegal ingredients and harmful.

   • Take 10ml of milk and add 2-3 drops of concentrated sulphuric acid slowly down the side (without shaking).
   • If a violet or blue ring forms at the top, it may indicate the presence of preservatives.

   Why it works: Formalin alters the reaction between sulphuric acid and milk components, causing a colour ring.

   Caution:Use protective gloves and proper ventilation - the acid is corrosive.

6. Test 6: Smell and Taste test

   • Pure milk should have a fresh, slightly sweet-creamy smell and taste with no strong aftertaste or an artificial smell.
   • Any soapy, metallic, or unusual taste may indicate adulteration or spoilage.

   Why it works: Milk’s natural composition gives a creamy sensory profile, and anything other than that is adulterated.

   Tip:Do this before heating the milk, as sensory cues are stronger when milk is raw.

7. Test 7: Visual & Boiling Test

   • Pour around 50 ml of milk into a transparent glass and let it settle for a couple of minutes.
   • After boiling, pure milk often forms a thick creamy layer (malai) on the top. If you see unusually thick, curdled bits or strange sediments at the bottom, it may be fake and adulterated.

   You should also ensure that the milk is off-white to slightly yellow. If it turns noticeably blueish, greenish, or deep yellow, it may be adulterated.

   Why it works: Adulterants and chemical additions alter coagulation behaviour and visual properties.

   Tip:Use a clear glass so you can easily observe sediment, layers, or residue.