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.


The Material World Class 4: Keen observation, and bouncy balls

In this class the younger group looked at properties of materials, and the older group were looking at materials processing.

I asked the children in the younger group to bring along a variety of small objects made of natural materials, and they brought some wonderful items.

items 5

items 3 items 2 items 1

We examined them under the magnifying glasses, again, and used all our senses except taste to find out what properties they had. I actually used an activity that Julie Bogart from Brave Writer calls ‘keen observation’. It might also be familiar to anyone who has tried mindfulness practices. We looked at the object with our eyes, looked at it under a magnifying glass, held it up to the light, touched it, stroked it, banged it, squashed it, listened to it, rubbed it on our cheek, rolled it up if we could, weighed it in our hands and smelled it.

The children liked saying what the items smelled like! Then the children came up with a couple of words to describe the item they were holding.

 Hard, soft, shiny, springy, silky, fluffy, ridged…

I was trying to get them to think about what properties are important when you want to make something or build something.

Would you build a bridge with pompoms?

Why not?

What would happen if a car went across it?

I read them the story of Mr Silly, who lives in Nonsenseland where things are not the same as they are in our world.

I think I could have done more quantitative work, e.g. getting the children to order the objects from lightest to heaviest and then weighing them to see if they were right. Or we could have classified the objects according to different criteria. But that’s something they can build on at home or in future classes.

I started off the older group with three problems that materials scientists have solved by using gels, and one that hasn’t been solved yet, but gels may be part of the answer.

(1)    Providing food for athletes in ultra-endurance events. The food needs to be lightweight, easy to digest (low in protein and fat), low fibre so you don’t need to poo during the race, doesn’t make your stomach feel like loads of liquid is slopping around, but also give lots of energy.

Scott Jurek. Image from
Sports gels, image from


(2)    Convenient way of delivering liquid medicines without people having to measure them out in small quantities using a syringe.

Household measuring spoons are not precise enough for measuring medicine. Image from
Gel capsules. Image from







(3)    Also a convenient way of delivering medicines that you don’t want to be digested until after the stomach.

Stomach and small intestine. Image from

(4)    This hasn’t been solved yet, but what if we could grow more teeth the way that sharks do? Currently, humans only grow teeth inside the embryo and then they push their way through our gums when ready. But what if we could stimulate our gum cells to produce teeth the way they do in embryos? (See this link from Harvard to find out how gels can promote tooth formation.)

Image from

Of course the ‘solutions’ themselves are not perfect. I particularly dislike the use of wasteful packaging for all these performance gels. Some athletes are trying to move back to more natural food for endurance events.

Nevertheless, all these are examples of how novel materials can lead to exciting developments in many different disciplines.

Discussion of gels led on to discussion of polymers and their structure at a microscopic or molecular level.

Image of cross-linked polymers. From

Then it was time for some fun, messy stuff – making our own bouncy ‘silly putty’.

There are many recipes for these on the internet. The problem is, many recipes that are circulating are just not reliable. Children can get very disappointed if you try an activity and it fails to give the desired effect. (Yes, it’s a learning experience, but not one you want to happen too frequently.) I used these instructions from the WOW lab at McGill University, Montreal, Canada, although we only had PVA glue so we didn’t make the latex equivalent.

 photo 1 (1)     photo 3     IMAG4138    IMAG4136

We just about had time to watch a video from the Canadian TV series How It’s Made, showing how robotic arms are manufactured. I didn’t have time to show the video of woven wickerwork or electrospinning, or tell them about Stephanie Kwolek inventing Kevlar. But here is a great video from Penn and Teller of a microbiologist turned fashion designer who makes fabric from milk.

Next week the younger group will be changing properties of foodstuffs, and the older group will start growing crystals.