We left our last science lesson making hypotheses concerning substitutes for buttermilk in the baking of soda bread. L10 postulated that a milk and lemon juice mixture would work just as well as buttermilk. We decided to test this. First she made up the substitute buttermilk. I asked her how she would do this. Her answer was a nonchalant ‘dump some lemon juice in some milk’. I asked how much? She didn’t really think it mattered. I asked her to think about the reaction, what was required to produce the co2. She said an acid-alkaline reaction. It was fascinating to watch her expression clear. With utter clarity she excitedly told me that she would need to test the acidity of the buttermilk using pH paper. Then she would need to match the acidity of the milk and lemon mixture to that pH:
We chatted a bit about having a control in the experiment and decided that the control would be baking a soda bread with plain milk in (pH7).
Each child took one of the breads to make. I looked up my recipe I used for soda bread, only to find that it used baking powder instead of Bicarb. Yes, I know baking powder has Bicarb in it, but I really wanted the children to use a Bicarb recipe. C10 did some research on the internet whilst I was foam painting with the littles and found and printed the perfect recipe. They all followed the same recipe, using the same ingredients bar the ingredient they were testing (Buttermilk) and used the same oven, pan and mixing bowl. One environmental factor we didn’t control was to have the same person bake all three breads. However, I planned to use that as a starting point to discuss factors to control within the experimental procedure, after we had finished. Here were the resulting loaves: One with buttermilk, one with our homemade buttermilk substitute and one with just milk:
The buttermilk bread was evenly risen and larger than the other two. The milk bread was the smaller, heavier loaf. These two results were expected. The children had hypothesised that the homemade buttermilk bread would be just as well risen as the buttermilk bread. This wasn’t the case. The bread made with homemade buttermilk had risen but it looked like it had risen quickly and unevenly. L10 at this point was looking a little sheepish! I asked what had she done? She said she hadn’t quite made enough homemade buttermilk and had needed to top it up. Instead of retesting, remeasuring the mixture, she fell back on her first thought of ‘dumping’ it all in!! So she had topped the homemade buttermilk up to the required amount and squirted some lemon in! We discussed how this might have contaminated the results by maybe making the mixture more acidic than the real buttermilk and therefore causing a more vigorous and quicker reaction. Hence the split, lop sided loaf.
We also decided to open up the loaves to see if there was any differences in the air bubble spaces:
One thing about the homemade buttermilk soda bread was that the bread tasted of lemon. It was only faint and of course could have been caused by that additional squirt of the lemon juice but it was a fact we had not considered.
I know for many this experiment would have proved frustrating. All that work ruined because of a squirt of lemon. I don’t see it that way. This experiment lent itself to much discussion of the experimental method (which granted we didn’t do terribly well at!). However, the children now have experience at hypothesising, choosing the control, controlling as many external factors as possible and we had the unexpected pleasure (!) of discussing contamination of an experiment. All in all a rich learning experience as well as a tasty lunch (and a very messy kitchen!)
I’ll be replicating this experiment with scones and pancakes, although I doubt I’ll post. Next week we will move onto baking powder, which contains Bicarb as one of it’s ingredients, and I’ll be asking how it rises a cake without any obvious acid being present.