Whilst my home-made Incr-Edible Science curriculum is primarily one of chemistry, my personal aim is to help L10 become knowledgeable in the ‘why’ of cooking, rather than just the ‘how’. L10 craves to be in the kitchen every spare moment and would like to run her own business linked in some way to cooking in the future. The joy of home-schooling is that I am able to tailor their education to that which they are likely to need to know to pursue their future career. I aim to teach all the children the chemical reactions which occur in their cooking. With that knowledge will come the ability to play around with recipes, to substitute ingredients and possibly design recipes of their own. This will be of interest to T11, who loves anything about chemistry, useful to C10 who hopes to run a home of her own one day, and essential to L10 who wants a future in the cuisine industry. It’s win-win all round!
So far we have learnt in-depth about the science of baking soda. For all my past Incr-Edible Science posts see here (they include posts about making fizzy lemonade, experimenting with soda bread and much more). For the past couple of weeks we have been learning how the industry exploited the acid-base reaction of baking soda and produced a more reliable product called baking powder.
First we went over exactly what baking soda does. I asked what reacted with it and why only certain baked goods use it in their recipe. They knew the baking soda was alkali which required an acid to produce the carbon dioxide, thus raising the loaf or baked goods. Therefore only recipes which contained an acid such as vinegar, lemon juice or buttermilk could utilise baking soda as a raising agent. I asked how cakes rose. They immediately said baking powder. I asked them how it might work. T11 suggested in the same way as yeast. It was L10 who thought it maybe contained baking soda and a dried milk powder or dried lemon juice. I liked this path of thinking, and told her she was heading in the right direction. The children understood that it needed to be dry to maintain its inert properties so that only when mixed with fluid a reaction occurred and not before. I told them the baking powder did indeed contain baking soda and a dried form of an acid. They immediately looked on the label which gave its contents: Sodium Bicarbonate and sodium dihydrogen diphosphate. Needless to say they were none the wiser!
We went shopping in our larder and they saw a packet of tartaric acid. Given acid was in the name, it was in our baking area of the larder and it was powder they suggested it might work! I had them read this first. Then I had them do a bit of investigation, with the goal being to create their own Baking Powder, which would work as effectively as the one bought from the shops.
Firstly they checked to make sure the baking soda or the tartaric acid alone wouldn’t do the job of producing carbon dioxide. They did this by mixing the same amounts of powder with water. There was no reaction.
I asked how they wanted to start experimenting. They suggested a test tube of baking powder, say a teaspoon, and a different test tube with a half teaspoon of baking soda and a half teaspoon of tartaric acid, to which they would add a pipette full of water to each at the same time and then set off a timer for a minute. I was to take a photo immediately after the water was added and 1 minute later. The reason for the minute delay was to see if the mixture was still producing carbon dioxide, which it would need to do if it was going to rise a cake:
We all had a chat about what we could use to slow down the reaction of the homemade mixture. T11 remembered talking about how the flour in the soda bread mixture probably helps slow down baking soda reaction, so he suggested we use some flour. He thought corn flour rather than normal flour to stop us making glue! So we tried it. This time we used half a teaspoon of each powder (bicarb, tartaric acid and corn flour) and compared its reaction with one and half teaspoons of baking powder:
I had them play about with differing proportions. They were unable to find a mixture that produced exactly the reaction in a test tube as baking powder did. T11 pointed out though, that a test tube wasn’t exactly the conditions it would be used in, so maybe it would in fact work inside the oven. They had noticed when they used 2 teaspoons of baking soda to 1 teaspoon of corn flour and 1 teaspoon of tartaric acid, the mixture seemed to continue to bubble. Not fizz but bubble. I came and took photos:
So we gave it a go. Each lunchtime, whoever is cooking lunch makes some soup and a batch of banana muffins. The recipe is really simple and requires 6 teaspoons of baking powder. We substituted our homemade baking powder, baked as normal and this was the rather delicious result:
Whilst I think T11 would rather be working with ‘real’ chemicals, the girls kept saying to me how much they loved our Incr-Edible Science! L10 said she would never want to go to school because she would never have this much fun in her science class. It makes all the hard work worth it when I get comments like that! They are learning to think, surmise, test theories and eat their chemistry lesson at the end. Could science be more fun?