It was a Sunday and late in the morning. Rini, a little girl of love her Sunday mornings, because a) on Sunday mornings she can get up late, b) after getting up she can take out her heap of storybooks and magazines, she can look at them one by one, read some of them or solve some puzzles given in them while lying on her belly on the small carpet laid in their living room. Her mummy and daddy also feel very happy on Sunday morning, no office, no school, no shopping and no hurry. They read the newspaper, Sunday editions or magazines, drink tea and eat breakfast, chat and laugh.
Along with this, Sunday morning brings another attraction for Rini. On Sundays, Rini and her parents cook together after having a late. Rini does not remember from when, but it has almost become a ritual now, that the Sunday afternoon meals are cooked by all of them together. Rini finds it very exciting as she can see many magic happening while they cook, her mummy calls it ‘food science’. She eagerly waits for this fun time for the whole week.
Today while turning the pages of her magazines and putting a spoonful of chocolate cornflakes in her mouth Rini could hear her parent’s discussion about lunch-menu. Her mummy was reading out loud a paneer (Indian cottage cheese) recipe and they decided to cook that. But for that they needed paneer, which they don’t have in stock. Her mother took a look into the freeze and found there was enough milk though, her mummy announced that they could tear the milk and make some paneer, all by themselves! Rini could smell some adventure here, she know what paneer is, her parents have also make it at home before, but she never knew that it was made after tearing the milk! She finished her breakfast very fast, collected all the spread out of her books and magazines, kept them back in proper place, washed her hands with soap (a rule they follow before starting to cook) and went to the kitchen to spy what her mummy was doing. Her mummy was beaming with a big smile. She told Rini, to start preparing for tearing the milk and keep the things she thinks they need for the job. Rini was little confused, but she did not want to show it. So she took a big saucepan to pour the milk, she took out the milk packets from the freeze and she took the kitchen scissors also (for tearing the milk!). Her mummy smiled, she said to tear the milk they might not need the scissor, she took out lemon from the freeze and squeezed out juice from them instead. Daddy was also there in the kitchen by now. They pour the milk in the saucepan and put it on the gas hob, and let the milk boil on low flames. Rini was very curious; she was sitting on a stool and was waiting for the milk to boil. As soon as it starts boiling, mummy gave Rini the lemon juice to pour slowly over the milk. Her mummy was stirring the milk. Nothing was happening for a while, but suddenly Rini saw that the whole layer of milk was crumbling into bits and pieces, and actually the milk was tearing away. Rini was very excited to see this; she exclaimed Mummy, look! The milk is tearing apart!
Her parents were clapping too, and they put off the gas flame. Took the paneer out in a cheese cloth and the watery stuff left, mummy was calling it whey was kept to add in a gravy or soup. Mummy said they can also use the whey for making paneer again, and then they will not need the lemon. They made a bundle of the cheesecloth and put some heavy utensil on it. This was to take out most of the water from paneer, to cut the paneer into cubes later. It needed some time and Rini was bursting with questions inside her. Her mummy knows her well, so she took her to the dining table, took out her kitchen activity notebook and brought some colour pencils from Rini’s pencil box, then she said ask.
Rini wanted to know why the very uniform milk suddenly tears away into pieces.
Mummy told that although the milk looks very uniform but it is an example of natural colloid where in the water, milk proteins, one of them is called casein and fat particles are floating. Colloid is a mixture where one substance is dispersed in the other uniformly but not dissolved like salt/sugar in water. The casein protein cages lots of calcium (the material our teeth or egg shells are mainly made up of!) ions inside it, these are known as micelles and that reflects all the light and gives milk the white colour too. There is other protein like serum protein is also there. There are other minerals like magnesium and sodium and many vitamins.
Rini asked how the casein protein could cage calcium? Whether they had hands?
Mummy smiled and said, “Then we need to know little more.”
She continued, “Proteins (the building blocks for growth) are made up of smaller units called peptides (like Lego blocks), some peptides in the protein have branches called phosphate residues on them and they are negative in charge and calicium ions are positive in charge so being opposite they attract each other like magnets. And outer layer of the micelles are negatively charged so two casein protein don’t come close to each other and they keep swimming away from each other. But all this is a very balancing act just like you saw that day how that girl in the fair was balancing on the rope.”
Rini was growing impatient and she said, okay, okay and then, how on heating and giving lemon broke the milk into pieces?
Mummy answered, “On heating we are destroying the balance and again on adding lemon juice reduces the negative charge on the surface of the micelles and it also brings out more calcium and phosphorous from the micelles as it is an acid and thus the micelles get damaged and the casein protein come closer stick together, many thousands of them together make the paneer.” “Do you understand now?” Mummy asked.
'Yes," Rini mumbled, "But how can we see all these proteins and vitamins floating inside the milk", She added. Mummy looked at her and said, think on that. She added, “Just like you need glasses to watch TV properly there might be something else to watch those substances inside milk.” Then suddenly Rini shouted, “ I know with a microscope!” Mummy smiled.
In the mean time daddy was busy collecting the ingredients needed for the special paneer recipe, mummy wanted to make and the paneer was also ready to be cut into cubes, so mummy and Rini again went into the kitchen for more fun and science.