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Understanding the science of bread

When learning to make bread it can be helpful to understand the basics of the science that is happening. 

When you understand what is happening in the dough and the transformations that are taking place you can learn to make adjustments to make even better bread. 

The composition of the wheat grain

An understanding of bread starts with the grain. The grain is the seed waiting to land in the soil, receive water and begin to grow. It is, therefore packed with the means to grow into a new plant and flourish. 

When we mill grains we have all of these component parts still in the flour waiting to perform their task of helping the seed to grow. When we add water to flour the enzymes, starches and proteins start to get to work in the same way they would if they were growing the seed, except this time their actions help to develop the dough and rise the loaf and contribute flavour to the baked loaf. 

Composition of wheat grain

A grain of wheat has an outer husk called the chaff, this is removed when the farmer cleans the wheat before it is taken to the mill.

80-85% of the grain is the starchy endosperm. It is this white part of the grain that makes up white flour.

When grain is roller milled, the outer layers of bran and the germ are efficiently removed to leave only the endosperm. When roller mills are producing wholemeal flour the bran and germ are added back in after milling.

When grain is stone milled this separation of the endosperm from the germ and bran is less efficient and when producing white flour through sifting after milling some of the bran and germ remains in the flour lending a beige colour and more nutrients to stone milled flour than roller milled. 

By law, mills producing white or brown flour (some of the bran and germ are removed) in the UK have to add calcium, iron, thiamin (vitamin B1) and niacin (Vit B3) to the flour.

The endosperm is made up of starch and proteins (including gliadin and glutenin). 

The majority of the nutrition of the grain is in the bran outer layers, especially the layer closest to the endosperm called the aleurone layer, and the germ.

The outer layers of the wheat grain contain fibre, mostly insoluble which is important for gut health. 

The germ is the embryo of the seed packed around with vitamins and minerals to support its growth as a seed. 

Proteins in flour and their role in gluten formation

The two proteins in flour that are important to bread making are gliadin and glutenin. These proteins form chains when water is added and form the network of gluten. 

Gliadin is made up of short chains and is responsible for the extensibility of a dough, in other words, how far it will stretch. 

Glutenin is made up of long chains and determines the elasticity of a dough, i.e. its ability to spring back to its original position. 

Good flour for the baker to work with requires a good balance of gliadin to glutenin. If there is too much gliadin the dough will be too slack and will flatten out in the oven, unable to support its shape. If there is too much glutenin the dough will be too elastic and will be difficult to shape properly.

The proteins in flour are complex and vary in shape.  Adding water to dough allows the proteins to link up. As we mix and develop the dough, these chains become stronger changing the dough from a slack mash to a taut dough that will hold a shape and spring in the oven. 

The protein content of the flour can only ever be an indication of its strength when making bread. It also has to have the right ratio of glutenin to gliadin and be worked correctly by the baker to make good bread. A wheat that shows 14% protein, which on face value would seem like a strong wheat suited to bread making may, for example, have a high level of gliadin compared to glutenin and be overly extensible. If this is the case, the baker may choose to use a pre-ferment to strengthen the dough and improve its elasticity. 

Most flour that you buy from the shops will have been expertly milled and tested for baking performance so you will probably never have to worry about glutenin and gliadin ratios, but it is helpful to understand what is happening in the dough as you work it. 

The starch in flour

The wheat grain is largely made up of starch as this is the largest part of the endosperm, which is the greater proportion of the grain. 

The starch in flour is a polysaccharide, which means it is a chain of sugar molecules. When you add water these sugar chains swell and absorb the water and gelatinise. 

Milling the grain damages some of the starch molecules, (typically 7-9%) and this allows the enzymes naturally present in the flour to get to work. 

Enzymes in the flour

Enzymes are present in the grain (and yeast) and their role is to break larger molecules into smaller molecules so that they can be digested and converted into energy. This would be their job if the seed was intact and growing into a plant and it is their job in the fermentation of the dough. 

There are a number of enzymes getting to work in your dough:

  • Alpha- and beta- amylase enzymes are breaking down the starches from complex sugars to simple sugars.
  • Protease enzymes are breaking down the proteins. 
  • Maltase enzymes break down the maltose into simple sugars.
  • Invertase enzyme, that exists in the yeast, breaks sucrose down into glucose and fructose. 

The importance of enzyme action

Once the complex starch molecules are broken down into simple sugars by the enzymes the yeast can then eat some of these simple sugars and expel carbon dioxide and ethanol. The carbon dioxide gets trapped in the gluten layers and begins to push the layers and create bubbles. The ethanol contributes to the complex flavour of the bread. 

Many of the sugars, broken down by the enzymes but not eaten by the yeast contribute to the caramelisation of the crust and the sweet, flavourful tastes in the bread. 

Our taste buds are not sophisticated enough to taste complex sugar molecules, we can only taste simple sugars. If we allow the enzymes time to do their job, the loaf will be more flavourful. If the enzymes can’t do their job then the bread is bland tasting and pale when cooked. 

The enzymes have to be given sufficient time to carry out their function, which is why a loaf that is proved for longer in cool conditions will always taste more flavourful than one that is fermented quickly in warm conditions. 

The role of starch damage

For flour to be good for baking bread the level of starch damage has to be between 7-9%.

Sometimes there is too much starch damage in a flour. This may be due to harsh milling or it may be that the grain sprouted before harvest increasing the amount of amylase enzymes in the flour which will cause them to break the sugars down too quickly in the dough. Too much starch damage leads to a weakened structure and a gummy bread. 

Too little starch damage can mean that it is too difficult for the enzymes to break down the larger starch molecules meaning fewer simple sugars for the yeast to consume and a bland tasting bread. 

Resources

Emily Buelher, 2006, Bread Science, The Chemistry and Craft of Bread Making (available as an ebook)

Peter Reinhart, 2007, Whole Grain Breads,