Hands-on Activities

What are curds and whey?

What are curds and whey?
trigga - iStock
What are curds and whey?
trigga - iStock
Food & Nutrition,  Home Economics,  Science
4,  5,  6,  7,  8

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AB 11 Science 24 (2003, Updated 2014) Unit C: Disease Defence and Human Health
NU 11 Science 24 (Alberta, 2003, Updated 2014) Unit C: Disease Defence and Human Health
NT 11 Science 24 (Alberta, 2003, Updated 2014) Unit C: Disease Defence and Human Health
SK 1 Science Grade 1 (2011) Earth and Space Science – Daily and Seasonal Changes (DS)
AB 11 Knowledge and Employability Science 20-4 (2006) Unit A: Applications of Matter and Chemical Change
AB 11 Science 24 (2003, Updated 2014) Unit A: Applications of Matter and Chemical Change
AB 10 Knowledge and Employability Science 10-4 (2006) Unit A: Investigating Properties of Matter
AB 9 Knowledge and Employability Science 8, 9 (revised 2009) Unit C: Environmental Chemistry
AB 10 Science 10 (2005, updated 2015) Unit A: Energy and Matter in Chemical Change
AB 10 Science 14 (2003, Updated 2014) Unit A: Investigating Properties of Matter
AB 11 Chemistry 20 (2007, Updated 2014) Unit C: Matter as Solutions, Acids and Bases
AB 12 Chemistry 30 (2007, Updated 2014) Unit D: Chemical Equilibrium Focusing on Acid-Base Systems
AB 9 Science 7-8-9 (2003, updated 2014) Unit C: Environmental Chemistry
BC 10 Science Grade 10 (March 2018) Big Idea: Energy change is required as atoms rearrange in chemical processes.
BC 11 Chemistry 11 (June 2018) Big Idea: Matter and energy are conserved in chemical reactions.
BC 12 Chemistry 12 (June 2018) Big Idea: Acid or base strength depends on the degree of ion dissociation.
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NS 12 Chemistry 12 (2009, 2019) Acids and Bases
NU 11 Knowledge and Employability Science 20-4 (Alberta, 2006) Unit A: Applications of Matter and Chemical Change
NU 11 Science 24 (Alberta, 2003, Updated 2014 Unit A: Applications of Matter and Chemical Change
NU 10 Knowledge and Employability Science 10-4 (2006) Unit A: Investigating Properties of Matter
NU 10 Science 10 (2005, updated 2015) Unit A: Energy and Matter in Chemical Change
NU 10 Science 14 (2003, Updated 2014) Unit A: Investigating Properties of Matter
NU 11 Chemistry 20 (Alberta, 2007, Updated 2014) Unit C: Matter as Solutions, Acids and Bases
NU 12 Chemistry 30 (Alberta, 2007, Updated 2014) Unit D: Chemical Equilibrium Focusing on Acid-Base Systems
NU 10 Science Grade 10 (British Columbia, June 2016) Big Idea: Energy change is required as atoms rearrange in chemical processes.
ON 10 Science Grade 10 Applied (SNC2P) Strand C: Chemical Reactions and Their Practical Applications
ON 10 Science Grade 10 Academic (SNC2D) Strand C: Chemical Reactions
ON 11 Chemistry, Grade 11, University (SCH3U) Strand C: Chemical Reactions
ON 11 Chemistry, Grade 11, University (SCH3U) Strand E: Solutions and solubility
ON 12 Science, Grade 12, Workplace (SNC4E) Strand C: Chemicals in Consumer Products
PE 10 Science 421A (2019) Content Knowledge: CK 2.2
PE 10 Science 431A (n.d.) Unit 2: Chemical Reactions
PE 12 Chemistry 621A (draft 2021) Content Knowledge: CK 3.1, 3.2, 3.3
QC Sec IV Environmental Science and Technology The Material World
QC Sec IV Science and Technology The Material World
QC Sec V Chemistry Chemical Equilibrium 
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YT 11 Chemistry 11 (British Columbia, June 2018) Big Idea: Matter and energy are conserved in chemical reactions.
YT 12 Chemistry 12 (British Columbia, June 2018) Big Idea: Acid or base strength depends on the degree of ion dissociation.
SK 11 Physical Sciences 20 (2016) Foundations of Chemistry
SK 12 Chemistry 30 (2016) Chemical Equilibria
NT 9 Knowledge and Employability Science 9 (Alberta, Revised 2009) Unit C: Environmental Chemistry
NT 11 Knowledge and Employability Science 20-4 (Alberta, 2006) Unit A: Applications of Matter and Chemical Change
NT 11 Science 24 (Alberta, 2003, Updated 2014 Unit A: Applications of Matter and Chemical Change
NT 10 Knowledge and Employability Science 10-4 (Alberta, 2006) Unit A: Investigating Properties of Matter
NT 10 Science 10 (Alberta, 2005, updated 2015) Unit A: Energy and Matter in Chemical Change
NT 10 Science 14 (Alberta, 2003, Updated 2014) Unit A: Investigating Properties of Matter
NT 11 Chemistry 20 (Alberta, 2007, Updated 2014) Unit C: Matter as Solutions, Acids and Bases
NT 12 Chemistry 30 (Alberta, 2007, Updated 2014) Unit D: Chemical Equilibrium Focusing on Acid-Base Systems

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It starts with curds and whey! Explore the basic chemistry behind making cheese in this hands on activity.

What You Need

  • 2 glasses or clear plastic cups
  • Homogenized or 2% white milk (not skim or 1%)
  • White vinegar – 5 mL (or 1 teaspoon)
  • Strong paper towels, coffee filter or cheesecloth
  • Lemon juice (optional for follow-up activity)
  • Tray or sink
  • Measuring spoon

Safety First!

Vinegar, lemon juice and baking soda will irritate sensitive skin and tissue. Do not rub your eyes while handling these items. Wash your hands immediately after you complete this activity.

What to Do

  1. Pour milk into a glass so that it is 1/4 full. Allow it to come to room temperature (this should take about 15 minutes).
  2. Carefully look at the milk. Describe what you see.
  3. Add 5 mL (1 teaspoon) of vinegar to the milk.
  4. Wait about 5 minutes.
  5. Swirl the milk around and look at the sides of the glass. What do you see? How has the milk changed?
  6. Use the paper towels, coffee filter or cheesecloth as a strainer to separate the curds (solid part) and whey (liquid part) in the tray or sink.
  7. Squeeze most of the liquid out of the curds.

Discovery

Milk is a mixture and contains water, sugar (lactose), protein, fats and minerals. The vinegar helps to curdle the milk. Curdling happens when the solids in the milk (the proteins and fats) clump together and form a new substance, which are called curds. The curdling is the result of a chemical reaction between the vinegar (acid) and the fats and proteins. You can separate the curds out of the milk by pouring the clumpy mess through a filter like a strong paper towel or piece of cheesecloth. The liquid that passes through the paper towel or cheesecloth is called whey. These are the same “curds and whey” that appear in the nursery rhyme “Little Miss Muffet.” Curdling can also happen if heat or salt are added to milk.

Curdling is what happens when you keep milk after its expiration date has passed or if it has been left unrefrigerated too long. This is what it means when people say the milk has "gone bad” - it will taste very different from milk that is still fresh. This “natural curdling” or spoiling is also caused by chemical reactions that create acids in the milk as it gets old or warm. Those acids cause the proteins and fats to clump together, however the milk actually spoils because of the growth of bacteria that also occurs during this time.

Curdled milk is still safe to cook with. You can also buy curds in the grocery store. In fact, cheese is actually made from curdled milk! Cottage cheese is a great example.

  • Vinegar is a weak acid and so is lemon juice. What happens when you add lemon juice instead of vinegar?
  • Learn more here: Cheese-making Process – YouTube (Video – 4:48 min.)

For more information on this topic check out these Let's Talk Science resources:

What’s happening?

Milk is a mixture and contains water, sugar (lactose), protein, fats and minerals. The vinegar helps to curdle the milk. Curdling happens when the solids in the milk (the proteins and fats) clump together and form a new substance, which are called curds. The curdling is the result of a chemical reaction between the vinegar (acid) and the fats and proteins. You can separate the curds out of the milk by pouring the clumpy mess through a filter like a strong paper towel or piece of cheesecloth. The liquid that passes through the paper towel or cheesecloth is called whey. These are the same “curds and whey” that appear in the nursery rhyme “Little Miss Muffet.” Curdling can also happen if heat or salt are added to milk.

Why does it matter?

Curdling is what happens when you keep milk after its expiration date has passed or if it has been left unrefrigerated too long. This is what it means when people say the milk has "gone bad” - it will taste very different from milk that is still fresh. This “natural curdling” or spoiling is also caused by chemical reactions that create acids in the milk as it gets old or warm. Those acids cause the proteins and fats to clump together, however the milk actually spoils because of the growth of bacteria that also occurs during this time.

Curdled milk is still safe to cook with. You can also buy curds in the grocery store. In fact, cheese is actually made from curdled milk! Cottage cheese is a great example.

Investigate further

  • Vinegar is a weak acid and so is lemon juice. What happens when you add lemon juice instead of vinegar?
  • Learn more here: Cheese-making Process – YouTube (Video – 4:48 min.)

For more information on this topic check out these Let's Talk Science resources:

Related Topics

Acids & Bases
Food Literacy
Food Safety
Mixtures
Observing