Curds and Whey
You will need: Skim Milk, Vinegar, Microwave Oven or Stove (adult must assist),
Glass Measuring Cup, Tablespoon,
Soup Strainer, Wide-Mouthed Jar,
Waxed Paper, Water,
Fine Weave Cloth (several layers of Cheescloth is ideal), about 30 X 30 cm
What to do:
With an adults help, heat one cup of skim milk in a microwave or on the stove. The milk should be very warm but not too hot. Observe and describe the milk. Add one tablespoon of vinegar and stir gently with the spoon. Observe and describe again. The milk will curdle and separate into white blobs and a clear yellowish liquid. Pour this mess into a cloth-lined soup strainer in the sink, with a wide-mouthed jar underneath. Dribble 3 or 4 teaspoons of water over the blobs that are in the cloth to wash the extra vinegar away. Pick up the corners of the cloth and gently squeeze out the remaining liquid. Unwrap and place the resulting lump on waxed paper.
You have just made the famous "curds and whey" of Little Miss Muffet. In modern form, the curds are a form of cottage cheese. Taste a bit of the curds. Milk is composed of mostly water with calcium and other minerals, soluble and insoluble proteins, vitamins, varying amounts of butterfat, and lactose (a naturally-occurring sugar). The vinegar (a weak acid) reacts with certain proteins in the milk to turn them solid (curds), leaving most of the water behind (whey).
Evaporate most (not all) of the water from the whey by using a microwave oven or the stovetop at very low heat (it will spoil if left to dry on a counter top or window sill). When cool, taste the resulting syrup. This is where most of the lactose ends up, and you can taste a slightly sweet flavour, along with the stronger taste of the vinegar.
The lump of curds is mostly a product called casein. It is most of the insoluble protein that was in the milk, so you can see that milk is really a good source of protein. If you place the soft lump into a blender, add 2 or 3 tablespoons of water and a half teaspoon of baking soda, then blend to liquefy, you get a very simple form of glue or paste that can also be made into paint that can form a very tough coating when dry. If you dry the lump instead of liquefying it, it actually forms a ball of hard, almost plastic-like material. These properties come from the drying out of the long, interlocking protein molecules.
At the library, research how cheese is made. Answer these questions:
1) What is used to form curds from milk (instead of vinegar) in cheese factories? Where does it come from? 2) What can whey be used for?
Other Variables to Try: (What Will Happen If I ...)
Try using cold milk instead of warm. Try using 1%, 2% or homogenized milk. Try using less vinegar. Try using more vinegar.
Curds and Whey (Parent/Teacher Page):
Applications to the Alberta Science Curriculum:
Grade 1: Applicable to the "Senses" Unit, when students use nearly all their senses to observe, describe and compare the before and after appearance, temperature, texture, smell and taste of the completely safe materials used in this hands-on experiment.
Grade 2: Applicable to the "Exploring Liquids" Unit, when students learn that water is a major component of milk; that 2 liquids can combine to make a solid (precipitate); and that materials dissolved in a liquid can be made to separate into solid and liquid forms. Students should also compare the properties of the liquids before and after the reaction. Also applicable to the Grade 2 "Hot and Cold" Unit, when students conclude that the reaction rate of the experiment can depend on the temperature of the components.
Grade 5: Applicable to the "Classroom Chemistry" Unit, when students see what happens when two liquids are mixed to make a solid; when a solid can be recovered from a liquid by a means other than evaporation (i.e. as a precipitate); and when students learn of the components that make up milk, and compare them with the products of the reaction. Students can also use indicators like litmus paper to classify the solutions being used as either acid, base or neutral, to compare with the products of the reaction. The following scientific terms and concepts can also be introduced and discussed: the Scientific Method, basic laboratory skills and terminology, solubility, acid/base/neutral, variables (most important for science fair!), suspension, precipitate, decanting, filtering, effect of temperature on reaction time, and the importance of accurate measuring. Students can also learn of real-world applications, as well as historical and nursery rhyme connections!!!
Answers to research questions:
1) Rennet, an enzyme extracted from nursing calfs stomachs, is commonly used to make cheese by causing the milk to "clobber" or create curds. Friendly bacteria can also be added to the milk instead of rennet. The bacteria then eat the lactose in the milk, and produce an acidic waste product that reacts like vinegar to "clobber" the milk, starting the cheese-making process.
2) Dried whey is used as an additive for many food products, such as ice cream, bread, margarine, sauces, some chocolates, etc., as well as animal feed. Read the labels on packaged food products you buy. The phrase "modified milk ingredients" often means dried whey.
Applicable science vocabulary:
precipitate, protein, casein,
decant, lactose, molecules,
filter, evaporate, variables,
acid, soluble, enzyme,
base, insoluble, bacteria.
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