Posted 18 September 2014
Television programme The Great British Bake Off is proving a popular Wednesday night choice for many households. But what about the science behind it all? Principal Lecturer in Crop Science, Dr John Reade, explains the journey from seed selection to the cooking process.
"The first question that you may ask is ‘what does a Principal Lecturer in Crop and Weed Sciences know about baking?’ Well, my strong background in science, my passion for food, and my design and delivery of school reach-out class ‘the science of bread’ has taught me quite a bit, and it has been a lot of fun too. And science is all around us if we look for it!
Before we even start thinking about flour, yeast and oven temperatures, we need to think about the wheat, or other cereal variety, that we are starting with.
Not all wheat is the same, in fact it is categorised into four groups. We do not want to be baking with Group 4 wheat which is grown to feed animals, instead we are interested in Group 1 and 2 varieties for bread-making.
Once growing, the wheat will need protecting from weeds, pests and diseases, and feeding with nutrients. This can be done in an integrated manner, using a variety of mechanical and cultural techniques, along with the use of agrochemicals and fertilisers. It can also be done organically, using mechanical and cultural techniques along with nutrient-building crops in the rotation and use of farmyard manure.
Protecting the wheat from weeds, pest and disease is not just about maximising the amount of wheat and hence flour that we get, and feeding the crop is not just about quantity. These steps are also about protecting and enhancing the quality of our product.
A wheat crop to produce good bread-making flour needs to have large endosperm, high starch content and good protein content with lots of gluten present. All of these factors can be affected not just by the variety chosen, but also by the way the growing crop is managed. The baker can be very thankful that the farmer knows how to manage their crops so well - applied science in action!
Harvesting the wheat at the right time will also affect the quality of the bread-making wheat – the farmer needs to continually assess the crop and carefully harvest it at just the right moment. This careful harvesting is vital – the presence of weeds, soil, stones and other contaminants are likely to cause the wheat to be rejected by the miller.
The science of milling is not just about crushing the wheat grains to get the flour out. In fact, it is not about crushing at all. The wheat grain is sheared and broken by rollers, which split open the grains but don’t crush and compact them. There is then a series of sifting steps that separate out the flour, the bran and the germ. The whole milling process, which has gradually developed from the use of stone querns thousands of years ago, can be considered to be science in its own right.
So – we have used the correct wheat variety, grown it in a careful manner, harvested it at the right time and carefully milled it to flour. What about the baking process? Well – that involves science too.
To start, the relative quantities of flour and other ingredients must be correct in order for successful dough to be made, much like the relative quantities of chemicals that are required for a chemical reaction to proceed correctly. A very basic bread recipe is given here. It is unlikely to win any prizes, but it will feed you if you are hungry and served as a useful one for my classes.
7.5 ml dried yeast and a pinch of sugar
450ml tepid water
700 g white flour
The yeast uses the sugar to respire as it grows, releasing carbon dioxide gas. The mixture of flour and water forms the dough.
The gluten in this dough has a wonderful property – it is elastic and it can stretch. As it is kneaded and then allowed to rest, the gluten allows the dough to capture and hold the carbon dioxide, much like inflating balloons.
When the bread is then baked it hardens in this risen shape, with many little air pockets and the expected bread crumb texture. But if the gluten is damaged by storing the wheat or flour at too high temperature, or by using a wheat variety with poor or little gluten, then the dough will not catch the carbon dioxide and the bread will not rise.
The result? A loaf that looks and feels like a building brick. Not the sort of thing you want to make your sandwiches with, but you can try to replicate this at home – place dry flour in a hot oven for 30 minutes and then try making bread with it. The heat will have damaged the gluten and the bread will not rise.
An understanding of the science involved in baking allows us to avoid problems such as this.
A wonderful journey from selecting the correct wheat variety through to the production of a perfect loaf of bread. The science underpinning The Great British Bake Off is an amazing subject indeed!