Question: What's the hardest experiment you've ever done? Why was it so hard and what was it?

Grant Campbell answered on 14 Mar 2013:

As I’ve written in response to a previous question, in modern breadmaking processes we mix the dough under a partial vacuum, to control the air content in the dough, in order to get a better bread structure. It works – but why does it work? That’s what I have spent a very long time trying to understand. It’s difficult because the bubbles in dough are very small and hard to measure, because dough is a very complex material and hard to do experiments on – you have to be a very skilled experimental scientist to get good results when you study bread – and because the mathematics that you need to use to describe and understand what’s going on is pretty difficult. So far I’ve shown that mixing under partial vacuum gives fewer bubbles in the dough (previously people thought that maybe it gave smaller bubbles, or more bubbles, but I was the first to show that it gives fewer) – but this then results in more bubbles in the bread, which is strange! I’ve also shown how the amount of air in the dough depends on the balance between how fast it’s mixed in and how fast it’s mixed out – again, this was surprisingly hard to quantify, because both the maths and the experiments are quite hard – but it’s important for understanding how to control the dough mixing process to get good bread quality.