Cottage cheese

Cottage cheese

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Further Resources
This task is about observations and conducting a science investigation.

Background 
Casein is the chief protein in milk and an essential ingredient of cheese. When rennet is added to warm milk it will cause the casein to curdle. To curdle 125 mL of reduced fat milk (1.5% fat), you would use 4 drops of rennet.

How to do this task 

  • You are the research chemist for a dairy company. The company is going to write pamphlets on how to make cottage cheese. Part of making this cheese involves the curdling of the casein in milk by using rennet. The pamphlet needs to tell those making the cottage cheese what would be a good temperature to have the milk at before adding the rennet. 
  • Your job is to trial milk temperatures of 15° C, 30° C, 45° C, and 60° C. You want the milk to curdle in a reasonable time, and for this product not to be too runny or too tough.
  • For each trial use 125 mL of milk and 4 drops of rennet. 
  • Carry out your trials and record all observations. 
  • Finally write up a report for the dairy company recommending a temperature, and the reasons for this choice.

Question 1Change answer

Observations

Question 1Change answer

Report summarising findings
Task administration: 

This task can be completed with equipment, pencil and paper or online.

Equipment:

Rennet (a brand name is Renco); 125 mL of 1.5% fat reduced milk; thermometers; beakers; Bunsen burner; eyedropper.

  • Once 4 drops of rennet have been added to the milk, it should be stirred gently.
  • Students will need to wait approximately 20 minutes for curdling to occur.
  • Rennet reaction may take place over a range of temperatures from 10-15° C to 60-65°C. The optimum temperature is between 40-42°C. No reaction occurs if the temperature is below 10°C or above 65°C. Low temperatures retard the reaction, making a more tender coagulum, while higher temperatures toughen the coagulum.
Copyright: 
Image copyright: NZCER.
Level:
5
Curriculum info: 
Science, Investigating in science, Material World
Key Competencies: 
Thinking
Keywords: 
chemical change, enzymes, temperature, rennet, report writing, investigation, observation
Description of task: 
For this practical task students follow a plan to determine the best temperature for the reaction of rennet with milk. Students need to make observations and write a report on their findings.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
Capability: Gather and interpret data
This resource provides opportunities to discuss the importance of controlling variables when using fair testing for an investigation.
Science capabilities: 
Gather and interpret data
Answers/responses: 

Observations to include:

  • Milk going from liquid to solid or no change.
  • Time taken for this change.
  • All four temperatures noted, with the observations.
  • Other observations, e.g., some clearer liquid can be seen, there is no colour change.

Report to include: 

  • States a preferred temperature and gives a statement alluding to both time taken to curdle the milk and the texture of this curdle.
  • States a preferred temperature and gives a statement alluding to either time or texture.
  • States only one of preferred temperature, time, or texture.