Separating pasta and rice

Having joined Instagram ( and Pinterest (, I have spent a while perusing other people's ideas for toddler activities.  Inspired by beautiful photos of rainbow coloured pasta and rice sensory play ideas, I decided to give it a go.  I did have some reservations about the likely length of time it'd be played with compared to the time taken to set it up, and about the potential for mess, but I was hoping to be pleasantly surprised...

I made some coloured rice, and some coloured pasta using one of the many suggested ways I read about - I used food colouring and a small amount of vinegar, shook them with the pasta or rice, left for about half an hour and then dried them.  It did give the kitchen a pretty overwhelming smell of vinegar, but the end result was quite pretty when added to some wholewheat and separated tricolour spiral pasta, and the colour doesn't rub off on little hands.

A colourful box of pasta and rice
I also had a science experiment in the back of my mind when setting this up, knowing that everything was going to end up mixed together.  It therefore didn't upset me too much when he dug straight in and set to work making colourful mixtures of the shapes in little plastic tubs, using a little scoop and some giant tweezers I'd put out for the purpose.  It occupied him for about 15 minutes which was longer than I thought, and after each colourful pasta and rice mixture was 'served' to me, we tipped it together into a litre wide-necked plastic bottle.  I quickly fashioned a funnel from a piece of scrap paper to reduce the amount of spillage after the first one went all over the table - in hindsight, it is obvious that was needed!

Jumbled mix of colourful rice and pasta

I asked the small boy what he thought would happen if he shook the bottle.  He said he'd give it a shake to mix the pasta and rice, so I screwed the lid on and he shook it vigorously...  I was quite pleased to see all the rice was working its way to the bottom of the bottle, and encouraged him to give it a bit more of a gentle side to side shake before taking a look.  He was a little puzzled after all his shaking to see that the result was the opposite of mixing! Instead of everything being jumbled together, the rice was at the bottom, the smaller pasta (macaroni) generally above it and the larger spirals and tubes at the top, although there was still quite a lot of mixing of the larger pasta shapes.

He muttered about the rice being at the bottom, and I remarked that it hadn't mixed, but had in fact sorted itself roughly by size.  He picked it up and gave it another shake to try and mix it, to no avail, in fact it separated a little better.  He promptly decided to go and play with something else!

Rice at the bottom, and then pasta sorted to some extent by size above it

So what happened?  This is an example of something called granular segregation.  You might have noticed it in packets of mixed cereal e.g. muesli or mixed nuts (sometimes known as the 'Brazil nut effect') where the different components of the mixture tend to separate.  There seem to be several explanations around as to why this happens, but for the purposes of a toddler experiment, it seemed to be enough to show that it didn't behave as he thought it would!

Sadly the shaking didn't perfectly sort the pasta and rice so that I could easily set out another nice neat tray to play with (although this was always optimistic given that there were multiple colours of the same shape...), but it did get the small one to make a prediction and test whether it was right.  It also gave a nice thing for his baby brother to shake with close supervision and watch the different colours and shapes move around.  In fact, I think the smallest played with it for longer in total than his brother.  We've since re-used the rice and pasta and added a few more shapes for 'pretend cooking', but the shaking in a bottle was a nice extension to what seems to already be a popular activity for small children.