Disappearing Ink

Imagine getting a secret note which only you can read. I would love that. As I was researching about this, I read that spies used lemon juice, milk, vinegar, onion juice or even urine as an invisible ink during the 1st World War. Low tech intelligence, I guess.

Try this fun experiment with your child with all the ingredients from your kitchen pantry.

Ingredients:

Any one of these or all:

  • lemon juice
  • vinegar
  • milk
  • 1 tbsp Baking soda mixed with 2 tbsp  water

cotton swab/ Q tips

white paper

heat source – lamp, iron box,  or a flame (Use with caution)

Directions:

Step 1: Dip the cotton swab in any of ingredients (lemon juice, vinegar, milk or baking soda solution)

Write with it on the piece of paper. Let it dry. I left it to dry and went back to it in an hour.

Step 2: Under parental guidance only

If using the light bulb, turn it on and let it heat up. I found using the iron box was easier.

light bulb: Hold it over the lightbulb for a few minutes and watch your secret message appear. Be careful not to burn the paper.

iron: Place paper between two pieces of cloth and iron.

open flame: Hold over an open flame and watch the message appear.

 

The science behind the experiment:

Most of the ingredients given are acidic except for baking soda. With baking soda, you can paint the paper over with grape juice. The color of the writing changes. This is because the acid (grape juice) reacts with the baking soda (a base) to discolor the paper.

Lemon juice, milk, and vinegar are acidic. The acid weakens the fibers of the paper. When heated, some of the chemical bonds break down and carbon is released. When carbon comes in contact with air (oxygen), the carbon in the paper oxidizes and turns brown. (A cut piece of apple also oxidizes (turns brown) but without heating)

 

Salad Dressings and Density of Fluids

A salad dressing always heightens the taste of a salad. The simplest salad dressing is oil, vinegar, salt, and pepper. You could add honey to sweeten it or some dijon mustard. Have you noticed that when you pour oil and vinegar, they do not mix? Have you ever wondered why?

Salad dressing reciipes1 (1)

Salad dressing reciipes1 (2)

I had written about density in my previous blog – Float or Sink, but here is a recap. Density is how much ‘stuff’ is packed in a certain volume. The density of a liquid is the mass per unit volume (1kg/m3). For all practical purposes, if you take 1 liter of liquid and measure the mass (weight on earth), the density of that liquid (for example) 1.2 Kgs, then the density of that liquid is 1.2/1 =1.2.

Here is an easy and fun experiment to do with kids about the density of liquids. If you color the liquids, it would be a fun addition to their room.

Use the same volume of liquids. I used 1/4 cup each.

The liquids I used were honey, vegetable oil, water, dish soap, and milk. I had to use a baster and add milk gently which I did not and it did not work, so I redid the experiment without milk. You can also add vinegar.

Ingredients:

  • 1/4 cup honey
  • 1/4 cup vegetable oil (you could mix an oil based food coloring)
  • 1/4 cup water mixed with some water-based food colour
  • 1/4 cup dish soap
  • a tall glass
  • cherry and other small objects

 

Directions:

Pour equal volume of the different liquids in cups and place them in order of liquids being added. (honey, dish soap, water, and vegetable oil.  I also labeled the cups.

Pour the honey carefully into the cup without touching the sides of the cup. Carefully add dish soap. If you have a baster, use that.

Then add water and then vegetable oil. It is ok if it mixes a little.

Leave it for an hour to settle, you will see the different layers.

Why does this happen? Liquids have different densities. The heavier liquids like honey have a higher density and therefore will sink below the lighter liquids.

Screenshot 2018-10-21 at 8.58.47 PM

The same rule for float or sink works here too. Denser solids will sink and solids that are less dense like a walnut will float. A cherry is denser than water and oil so it settles on top of the honey. Try different objects, how about a ping pong ball. Experiment with different liquids like vinegar, baby oil, lamp oil, corn syrup or maple syrup. Ask your child to hypothesize and then document the results.

20181016_151340
Adding solids to the liquids

 

 

 

 

 

 

Kitchen Science – Sink or Float – Bobbing for Apples (and other vegetables and fruits)

It is almost Halloween and this game is often played by children. So the question is do all apples float? That led to more questions – what about pumpkins, lime, banana, pomegranates or coconuts? Why do they float or sink? Inspired by the thought, I decided to check it out on my own. I started with an apple, pomegranate, and coconut. I then started taking vegetables out of my fridge and started playing with what I have. There were some surprises.

So here are my results:

Fruits and vegetables that float: apple, banana,  tomato, madras cucumber (squash family), coconut, eggplant, capsicum and believe it or not, watermelon.

Fruits and vegetables that sink: pomegranate, lime (surprises), potato

Why do coconuts and watermelons float? Think about it!

Why do some sink and some float?

This is because of the density of the fruits/ vegetables (in this case).

Density is defined as mass per unit volume or the measure of how heavy a substance is for its bulk or volume. But what does density have to do with floating or sinking? We all have heard about Archimedes, the guy who ran out of his bathtub into the street, butt naked, shouting  “Eureka”. But do we know why he shouted Eureka? Well, he discovered the principle, ‘The Archimedes Principle’ that governs whether an object floats or sinks in a fluid. He is also credited for calculating the value of pi.

Explanation of Archimedes Principle: Archimedes Principle states that when an object is immersed in a fluid, the buoyant force is equal to the weight of the fluid displaced by the object. This is what we learned in school. But what does it mean?

Let us go back to our bobbing of apples. If our bowl is filled completely with water and then an apple is added to it, some water spills out (just like the water that spilled out of the bathtub when Archimedes got into the tub). If you weight the water that spills out, it would equal the upward force (buoyant force) on the object. From that buoyant force, the density of the apple can be determined. or we can also say that the apple is kept afloat (buoyed up) by a force equal to the weight of the water it displaces.

So, if the object’s (vegetables and fruits in this case) density is less than that of water, it will float and if its density is greater than that of water, it will sink.

Let us look at examples in the kitchen while cooking.

  1. When ravioli, and gnocchi are cooked, they first sink when you put them in the boiling water. This is because they are more dense than water. But as their starch granules expand in the hot water, their density decreases. When their density becomes less than the density of water, they float and we know that they are cooked.
  2. When we fry vadas (Indian savory fried snack) or doughnut holes in hot oil, they are less dense than oil and floats. But as the bottom surface cooks, it loses water and becomes more dense. The bottom is now more dense than the top and it turns and cooks on the other side.

Sources:

Wolke, R. L. (2005). What Einstein Told His Cook 2. New York: W.W. Norton and Company.

https://www.livescience.com/58839-archimedes-principle.html

 

Vendakkai Pachadi – Okra in a Spicy Tangy Coconut Gravy Why is Okra Slimy and What can you do?- Science in the Kitchen

After a long time, I decided to make Pachadi as a side dish for rice and Molagootal. I looked up a few of my recipe books including Samaythu Par and could not find the recipe. I then looked online and could find variations but not what I wanted. So I called my parents to get the recipe. This I assume is the Palakkad version of the dish.

Okra is also called Lady’s finger in some parts.

You could prepare the same dish with eggplant or white pumpkin too.

Why is okra slimy? Here is some science behind it!

I came across an article on NPR that talked about okra and then visited the blog, botanist in the kitchen. Here is the explanation as to why okras are slimy. Okra is slimy because of a water-soluble mucilage. It is an adaptation to retain moisture and store water in hot ares where they grow. Though there is no information as to why exactly it is slimy, there is enough information as to how to remove the slime while cooking.

In India, our mothers and grandmothers have been using acid to remove the slime. Tamarind is used in the south, but sometimes yogurt or lemon juice is added, depending on the recipe. The viscosity (the measure of a fluid’s resistance to flow, in this case, the thick, sticky, semifluid consistency) reduces at high heat around 90ºC. Then even when it is cooled, the mucilage does not return. Another popular way in India and Africa is to add an acid. Viscosity is at its peak at a neutral or alkaline pH, by adding an acid the mucilage becomes acidic and the viscosity reduces.

Ingredients:

300 grams okra/ ladies finger

1/2 cup white pumpkin or madras cucumber (optional)

tamarind paste 1 1/2 tsp (or fresh tamarind 1 inch diameter piece soaked in warm water and pulp removed)

1/4 tsp turmeric powder

salt to taste

1/4 tsp jaggery/ brown sugar (optional)

To grind to a paste:

1 tsp mustard seeds

1-2 green chillies

1/2 cup coconut

To temper

1 tsp oil

1/2 tsp mustard

1/2 tsp urad dal

a pinch of asafoetida

a couple of curry leaves

Directions:

Wash and pat dry the okra. Cut into small pieces.

In a pan, add the vegetables, tamarind paste, a cup of water, salt and turmeric powder. Let the vegetables cook.

Grind the coconut, chilli, and mustard to a paste.

When the vegetables are cooked, add the paste and let it cook for 10 minutes on a slow flame. Add brown sugar if you feel it is too sour. It has to have the right balance of sourness from the tamarind and the spiciness from the chilli

Heat oil to temper. Add urad dal, mustard, asafoetida, and curry leaves. When mustard splutters, add it to the gravy and mix.

Serve as a side dish with rice and molagootal (or any gravy without tamarind).

Source:

Okra – what’s not to like?

 

Kitchen Science – We are all Chemists! Yeast Talk

I wonder if I can add chemist to my profile which includes baker, cook, teacher. While writing the blog post on pizza, the teacher in me started wondering about the science behind making pizza. This morning I made appam and stew and seeing the small holes in the appam, I was explaining why it had those holes.

In every south Indian house, for generations, (before dosa and idli batters came in bags in the cold section of a supermarket), cooks ground the batter and left it overnight for it to ferment. Every Indian household made yogurt using a starter, heating the milk to the right temperature, adding the starter, keeping it in a draught-free warm place for it to set. That is chemistry.

Most kids think of chemistry as blowing up stuff; hardly thinking that cooking and baking involves chemistry. Yes, we bakers and home cooks do not wear lab coats and look cool in safety glasses, but we do make chemical reactions happen and know how and why some things work. One of the books, I love and learn from is the book by Robert Wolke, professor of Chemistry and author of the book, What Einstein Told His Cook. He explains the chemistry and the concepts behind cooking in the kitchen. He encourages asking ‘Why’ something happens. Encourage your child/student to ask questions – the scientific process starts with a question!

20181009_174212

Since I was baking pizza and making appam today, I decided to look more closely at yeast.

What is yeast?

As I taught my 5th graders, yeast is unicellular fungus (microbe). It is a living organism.

What is the Scientific Name of Baker’s Yeast?

Saccharomyces cerevisiae. It means ‘sugar-eating fungus’

Where are they used?

They are used to make bread and beer amongst other things. They are also used to mold cheese and make antibiotics. Yeast is studied extensively in biology as an ideal experimental organism.

What do they feed on?

The yeast is dormant till it comes in contact with a liquid. Yeast loves sugar in various forms (sucrose, fructose, glucose, maltose). That is why when yeast is used, a teaspoon of sugar is added to the yeast along with lukewarm water. The yeast, however, continues to eat the sugar in the dough.  Fermentation is the process of breaking down of the starch into sugars for their energy.

Why are they used in baking and other cooking?

The by-product is carbon dioxide (CO2) and ethyl alcohol or lactic acid which it gives out and is very useful for bread. When the carbon dioxide cannot escape from the dough because it is elastic and stretchable. This makes the dough rise and cause air bubbles in the dough. The ethyl alcohol produced during this process has a particular aroma and taste which we can taste in the bread.

Perfect Temperature

The optimum temperature for yeast to grow is 27º – 32º

This is what my pizza dough looked like from proofing of the yeast and the rising of the dough:

 

Fun Fact:

It takes 20,000,000,000 (twenty billion) yeast cells to weigh one gram.

Yeast Experiment

Note to parents and teachers: Before you explain to your child/student what yeast is and what it does. let them conduct the experiment. This is a simple experiment which can be done in groups. Let the child hypothesize what could happen. Different groups could change the amount of yeast or sugar or amount or temperature of water and hypothesize what could happen. Let them feel the wonder and awe while watching the balloon inflate. Then this leads to inquiry and learning.

A fun experiment to do with the kids to show the process. This is a slow process which takes around 20 – 30 minutes. So you start it and watch it every 5 minutes. (I did this experiment one evening at home – the balloon was inflating even after I threw it in the dustbin).

In a bottle, add 1 tbsp yeast (active dry yeast), 1 tbsp sugar, ½ cup lukewarm water and place a balloon over the bottle. Observe what happens.

Children can change the amount of yeast, sugar, and temperature of water and hypothesize what may happen. (changing one condition at a time)

Why does the balloon inflate?

The yeast feeds on the sugar and produces carbon dioxide. As there is no place to go, the gas fills the balloon and the balloon inflates. The very same process that happens in bread when the dough rises. The carbon dioxide fills a lot of balloon-like bubbles in the dough which gives the bread an airy texture.

Sources:

https://www.stufftoblowyourmind.com/blogs/yeast-bread.htm

https://redstaryeast.com/science-yeast/what-is-yeast/

https://www.exploratorium.edu/cooking/bread/activity-yeast.html