THE ONSCREEN chemistry between Paul and Mary, nevermind between Mel and Sue, completes the bake off. Sadly, only Paul will remain when GBBO moves to Channel 4 from the BBC, causing controversy and a Twittersphere explosion. No more soggy bottoms, however will we cope?
Enough about the heartache, let’s delve deeper into the chemistry behind the baking to achieve the honoured Paul Hollywood handshake.
Yeast is an important ingredient in bread baking, helping the bread to rise during the vital proving period. Yeast is a living organism and in order to respire it consumes sugar (from the enzymatic breakdown of flour) and releases CO2 and alcohol. This fermentation also gives bread its beautiful smell and flavour, as the carbon dioxide and alcohol react with the air causing an acidic environment in which large molecules are broken down into their constituents, such as carbohydrates into their smaller sugars, and proteins into their amino acids in addition to the natural enzymatic processes in yeast. The rate of anaerobic respiration, or fermentation, in yeast eventually starts to decrease as its own alcohol production inhibits it in a feedback inhibition pathway. The yeast is also killed off when exposed to high oven temperatures.
During kneading, the proteins in flour mix with water and bond to each other forming stretchy gluten fibres which trap the CO2 in small air pockets. This allows the bread to rise as when more CO2 is excreted into the pockets, the larger the pockets get, like inflating a balloon. Baking soda also releases CO2 to help the mix rise but requires an acidic ingredient with it for activation and neutralisation of the base produced, as there is no yeast to naturally start fermenting. Baking powder is added to normal flour to make self-raising flour, which is easier than using baking soda as it already includes the acid in the correct stoichiometry to neutralise the basic by-product.
To make your own self raising flour, a heaped teaspoon of baking powder is needed for 150g of plain flour. Once the dough is in the oven, the Maillard reaction, which is essentially amino acid-catalysed caramelisation reactions in which a sugar aldehyde or ketone is converted to an unsaturated aldehyde or ketone. This reaction takes place in which sugars and amino acids react at high temperatures to generate new flavours and aromas. The amino end of the amino acid attacks the carbonyl group of the sugar in a nucleophillic attack mechanism. These are evident as the bread browns and darkens.
To finish the baking process, caramelisation occurs in which the sugars breakdown further and release steam. More flavours are added to the bread from diacetyl (caramel), furans (nutty), esters and lactones (cyclic esters) give a rum flavour and maltol gives the toasty flavour. Sugar is often thought of as just a sweetner; this is untrue. In baked goods, sugar is also involved in several other processes. It undergoes a series of complex browning reactions above 160 degrees celsius, and the products of these form the brown crust of many baked goods.
Chemistry really is everywhere. It may not be thought of as being a large part of baking, but without it, self-raising flour and tasty bread wouldn’t be either understood or made. Maybe Paul does know what he’s on about.