Practicing Thermodynamics & Kinetics through making Ricotta

July 11, 2021

As many families with young children across Australia have to go through lockdown again, The House of Fun is back with some new activities to enjoy. You don't have to be in lockdown to have fun, but you need to have fun if you are in lockdown.

Every Friday at The House of Fun we practice some thermodynamics and kinetics through making Ricotta cheese.

At room temperature:

Add a few drops of lemon juice into 1 glass of milk.

Observe.

Nothing happens.

Leave it there. You can use it later to make a smoothie.

At high temperature:

Pour 1 l of full cream milk into a pot and bring it to boil.

H&S alert with children, make sure the adult does this operation & constantly supervise your children. 

After it is about to boil out of the pot, switch off the stove.

Wait 1 minute and pour in 25 ml of lemon juice. 

Magic. It curdles. Put a lid on. Wait 30 mins.

Add a pinch (2 or 3 as much as you like though the less the better) of salt. Stir and use a skimmer to separate the curds from the whey (the watery yellowish solution) and put it into a container with holes, like in the first two pictures. If you don’t have it, just use a colander with a fine net, as in the other pictures (from my friends). In either cases, allow the extra whey to flow out for a few hours. 

Do not throw away the whey. Never. Freeze it. Soon I’ll tell you how to make bread and bechamel with it.

Pour your container upside down on a plate. There you are. Ricotta. Awesome.

What happens?

Milk is made of water, proteins (mostly casein), fats and sugars.

Normally, casein particles floats around. They don’t aggregate because they are negatively charged and repel each other. In acidic environment, charges are neutralised and so they aggregate, trapping the fats in their net.

This process happens very slowly at room temperature but heat speeds it up. 

It’s great to make something yummy to eat and at the same time learn how heat can affect chemical reactions and physical processes.

Depending on the age of the children, you can leave it there (as I did) or engage into a more detailed scientific discussion.

Here a good source https://www.scienceofcooking.com/why-does-milk-curdle.html

Materials High temperature:

25 ml lemon juice

1 L full cream milk

1 spoon

1 pot

1 lid

Salt

A colander with fine net (the cylindrical container with holes found in some brands of ricotta would be the perfect choice)

A container to collect the sierum 

Materials Low temperature 

Few drops of lemon juice 

1 glass of milk

Learning outcomes 

Make ricotta 

How heat can affect chemical and physical processes