The Material World Class 5: Bread rolls, fairy cakes and crystals

I love cooking, and I love science. ‘McGee on Food and Cooking‘ is one of my favourite non-fiction books, and Heston Blumenthal one of my favourite celebrity chefs. Materials science easily overlaps with food science, so this term’s topic was an ideal way to share some of my passion with the children.

Both groups covered similar material in this class. We looked at how egg white changes when cooked, and when we whisk air into it. We looked at yeast (which bubbled more successfully in the second class).

We carried out the classic bicarbonate plus vinegar experiment, then introduced baking powder and discussed why this might be a better, more controlled way of creating bubbles in cooked foods.

To illustrate how yeast works, and how we change the properties of materials, the younger group made some bread rolls. I suggested a small experiment to see how much difference it made whether we kneaded the dough or not. It was great to see how much they all enjoyed the hands-on aspect. The room was probably the quietest when the children were focussing on kneading the dough.

I admit that I went overboard! I prepared too much for this class, in terms of the breadth of subject matter. I wanted to show the children

-how egg proteins change with cooking,

-how wheat proteins change with cooking,

-how yeast works

-several different ways to introduce gas, or air, into cooked foods.

Covering all these could easily take three sessions, and I probably should have narrowed my focus a little. I was also not quite on the ball in terms of having the equipment to hand while doing demonstrations (and I probably should have started off with the bread dough instead of trying to fit it in at the end). I still had good feedback after the class and the children had some great questions, which is always reassuring as it shows they are really thinking about the topic.

Demonstrating that sand is insoluble in water
Demonstrating that sand is insoluble in water
Dissolving salt in water
Dissolving salt in water

In the older group, we introduced the terms soluble and insoluble, miscible and immisciblereversible and irreversiblephysical reaction and chemical reaction. It was interesting to hear their ideas about how we could retrieve the salt from the water, or the sand from the water! I set them some homework – to ask a barista how come the coffee grounds don’t go in the coffee that people buy. Let’s see what answers they receive.

They made some mini fairy cakes to illustrate how baking powder works, and enjoyed topping them with caramel or chocolate syrup and eating them straight away.

The older children also looked at crystallization. I was relieved, after my failure last year, that my ‘fast crystallization’ demonstration actually worked. I had made up the supersaturated solution the night before the class, and introduced some seed crystals on a pipe cleaner at the start of the class. Watching carefully, we could see the crystals forming in solution and falling to the bottom or adding to the growth on the pipe cleaner. It wasn’t quite as exciting as some rapid crystallization videos on YouTube (like this one with sodium acetate) but the boys were still impressed, and I was satisfied.

sodium carbonate crystals growing from a supersaturated solution
sodium carbonate crystals growing from a supersaturated solution

They each took home a solution of sodium carbonate with a pipe-cleaner star to grow ‘snowflake’ crystals.

photo 1 (4)

In the next two weeks, the children will be bringing their own ideas for experiments and demonstrations, loosely based on the topic of The Material World. We will try them out in class and discuss how and why we get the results we do. I think it will be loads of fun. We have now pretty much covered everything the NSW syllabus expects children to cover at these stages (Stage 1 and Stage 2). There are a few other things we can talk about, but they won’t take long. I am looking forward to the children’s input, and to work that is not constrained by the syllabus. I am planning a few surprises on the last day, too.


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