When Physics meets Poori
A physics lesson between mother and son right in the kitchen.
I had just placed the oil over the stove and my younger son was ready with his plate. ‘Poori..Poori..’ He began to demand. I started explaining him how to roll to contain his curiosity and gain some time building the Poori pipeline. An inspiration from that conversation..
Poori is a wheat based Indian delicacy that is deep fried in oil and enjoyed with hot Potato or Chickpeas Curry.
Mommy, what is Poori made up of?
Poori is made up from Wheat my dear.. It has a protein called Gluten. When we add water to make a firm dough, the Gluten turns elastic and binds the dough just like glue. Gluten & Glue.. See the connection? Similarly, the Udat dal in idli dosas and egg and wheat in cakes provide the binding function..
You mean like Chewing Gum? Can I see some Gluten?
Sure.. Take a spoon of wheat flour and place it in your mouth.. Slowly allow the fiber and soluble ingredients to get dissolved.. What is left in the mouth is Gluten.. I wish I had wheat grains to give it to you.. We used to chew wheat and extract Gluten for fun as kids.
So elastic right.. Think of the damage to your stomach when you have food concentrated in Gluten.. Now you understand why Mommy is not happy with white pizzas and white breads?
All Right.. Tell me how to roll Pooris..
It is a simple 3 step process..FIRM, DUST & ROLL — Take a small portion of dough in between your palms and make it smooth and making the elasticity uniform. Dust both the sides of the portion with flour. The flour reduces friction with the base..otherwise..it is stubborn and it sticks.. Think of the flour as tiny ball bearings on which the poori will be stretched and rolled.
Keep the rolling pin in the centre and palms on the edge of the rolling pin.. As you roll your palms forward backward on and on, the dough gets flattened.. If your hands are farther from centre… greater is the spread of the rolling pin..
Think gears and cog wheels.. Small wheel moving the big one…Edge of the rolling pin is tinier compared to the central part.
Mommy, How are your Pooris rotating?
That is a secret dear boy !! Typically once it is stretched in one direction, people rotate and repeat the process.. Here is the trick for Perpetual rotation while rolling.. Using a slight sideward force aka Centripetal force, the manual turning can be avoided.. Give the left palm more freedom of movement and right palm only linear up down. Voila.. the Puri disc starts rotating by itself. It should come with practise and not as easy as told.. No more manual rotation and shapeless forms !! Totally uniform and round, this is the best technique for fast and round rotis pooris.. I mastered this as a kid making papads at home helping my Mommy.. And hope to teach you some day.
Have you seen how Pizzas and Naans are tossed in the air by the Master Chefs? Well behind the scenes, they are giving a slight sideward or tangential force along with the upward toss.. The Hula hoop, The Bay Blades and the Earth keeps rotating using the same principle ..
I like my Pooris to be totally Puffy. How does that happen?
Now that we have rolled enough Pooris, it is time for deep frying. The hot oil temperature is about 170 D Centigrade which is much above the boiling point of Water. This causes water in the Pooris to evaporate and roast the surface.. On the inner side, Water vapour starts to expand and this trapped vapour causes the swell.. This also explains why the rotis puff. So better eat your puffed Pooris quickly before the steam is out..
Mommy, I see you bouncing the Pooris..
Well..I learnt it that way..After sliding the Poori in the oil, gently press it downwards and Wow..Newton’s third law Every Action has an Opposite Reaction ensures that the Poori rebels and swell upwards.
Let me think of the science behind..May be pressing action causes more heating and steam to be trapped rapidly, so faster it puffs.. Physics rocks right??
Can we drain off some extra oil Mommy?
Have some paper napkins above and below the Pooris.. The paper has a lot of tiny pores. Like oil ascending on a dry wick, the paper will blot some oil.. Think of tiny tubes like our Capillaries. This phenomenon is also called as Capillary Action my boy..
Mommy, Kitchen is an amazing laboratory to learn Science.. Time to savour my Pooris..
