Question: whats the hardest thing you have ever had to find out and are you still trying to figure out anything thats quite interesting?!!

Grant Campbell answered on 13 Mar 2013:

Hi Rosie. During my PhD I was trying to measure the size of bubbles in bread dough (because the bubbles in dough grow to become the bubbles in the bread, so the size and number of bubbles in the dough has an important effect on the quality of the bread). Bubbles in dough are very small – on average about 1/10th of a millimetre, so hard to see and measure. I used to take thin slices of frozen dough and measure the size of the holes appearing on the slices. But, if you think about it, a round bubble is likely to be sliced off-centre, so that the size of the hole that you see is, on average, smaller than the size of the bubble from which it came. Also, larger bubbles have a greater probability of being sliced than smaller bubbles. It took me a long time, and stretched my poor brain a lot, to work out the mathematics to calculate what the actual bubble size distribution was!

One of the things we do to control the size and number of bubbles in bread dough is to control the pressure during mixing. If we change the pressure half-way through, that changes the bubble sizes, but I would really like to understand that process better. To do this I’d need an X-ray machine to measure the bubbles (which would be a lot faster and more accurate than by slicing method), and would need to develop some even more complicated mathematics. But that’s my particular dream, to be able to do that investigation, because it would be interesting and would have practical application for improving bread.

Thanks for your question – I enjoy explaining about bubbles in bread.