A is for acidic apple art

I've started doing some letter-themed days with my boys now the little one is 18 months old and beginning to show some interest in the alphabet. Starting with A, we did a variety of things including a bit of science with the A theme extending to acidic apple art with anthocyanins (the pigments that give red cabbage its colour)!

We've got an apple tree in our garden which is producing lots of windfalls this year.  These tiny, under-ripe apples are not very nice to eat (as my 3 year old discovered when he insisted on trying one) because they're really acidic.  As apples ripen, the proportion of sugars compared to malic acid changes and they get nicer to eat!  However, I thought we could use their acidity to do a colour-changing science activity.

Windfall apples and red cabbage liquid ready to use

We've still got some red cabbage cooking liquid in the freezer, so I defrosted a portion.  I drew the outline of an upper and lower case letter A in permanent pen on some printer paper and painted the shapes with the red cabbage.  I left the rest of the red cabbage liquid and the paint brush in a bowl for my son to use.  I cut up a few windfall apples, removing the bits which were rotting, giving him some irregular shapes to explore.

Apple imprints on kitchen roll

He made prints of the apples on some kitchen paper to begin with, and noticed they were making the paper wet, although it didn't change colour.  We talked a bit about the shapes, and I asked if he thought the apple was acidic or alkaline.  He thought acidic (we've talked about sour tastes corresponding to acids before, and he knows that we often use juice from lemons as an acid in our science activities).  

Patterns on the cabbage-painted A

To check if he was right, I suggested he made prints of the apple pieces on the letter 'A' that I'd coloured with the red cabbage, and it instantly turned pink.  The juicier bits of apple worked best, although he discovered that if he pressed it hard enough, crushing the apple released more liquid and gave a brighter colour change.  

Patches of pink and purple

I then suggested he painted the kitchen roll with the red cabbage liquid to see whether the apple prints turned pink.  He had a go, found the liquid turned from purple to bright pink in a few patches.  He then decided he could think of a quicker way to do it than using the brush and poured the liquid all over. the kitchen roll...  This did work, and was indeed faster, although it gives a blurrier outcome as it was very wet, and some of the malic acid dissolved in the red cabbage liquid so the pink colour spread beyond the original boundaries of the imprints.  Still, it gave a pretty patchwork effect, with his dried creation later reminding him that A is for apple and for acid!