- 100 mL of the type of milk being tested was measured and poured into a 150 mL beaker.
- The milk was poured into a stainless steel pot and heated to 55°C.
- Using a plastic Pasteur pipette, approximately 20 drops of vinegar were added to the milk while it was continuously stirred until the solution turned colourless and a mass of casein protein formed. Warning: Avoid adding too much vinegar since it may cause the lactose to hydrolyze forming glucose and galactose, making it impossible to isolate.
- A funnel lined with a filter paper disk was used to filter out the casein from the solution.
- A mortar and pestle were used to crush a chalk (4g) into powder.
- Poured the chalk powder into the solution.
- The solution was poured into a stainless steel pot and heated to 60°C.
- Once the remaining protein (albumin) precipitated, the protein was filtered out of the solution.
- Added 60 mL of 95% ethanol to the solution.
- The solution was poured into a stainless steel pot and heated to 55°C.
- Once lactose crystals formed, the solution was cooled for three minutes.
- The lactose crystals were isolated from the solution using filter paper and dried.
- Once the lactose crystals dried, their weights were measured using a weighing scale.
- Recorded the weight of the lactose crystals.
- Repeated steps 1-14 three times for each milk in order to be able to take an average of the lactose weight readings to ensure accuracy.