Sunday, September 20, 2009

Flour: Protein Content

Didier Rosada talked at length about flour during last week's Artisan III workshop, detailing the testing process by which the miller determines the ash content, the protein content and the level of enzymes. Proteins are organic substances made of carbon, oxygen, hydrogen, nitrogen and minerals. Wheat proteins are diverse and complex. 80% of them are insoluble in water and, when hydrated, link together in chains to form the gluten. In other words, water-insoluble proteins are what provides elasticity to the dough. Gluten is mostly protein and protein can absorb up to 250% of its weight in water but it does it much slower than starch. That's why it is essential not to switch to second speed too fast when mixing. Since starch - which fills the space between the gluten structure - gets hydrated first, the fact that dough is formed doesn't mean that the gluten has been fully developed. There are two ways of measuring the protein content of a given flour, near-infrared technology (NIR), a very fast and fairly precise method and nitrogen combustion, a much lengthier but much more precise process. NIR is most frequently used. Some countries also measure the proportion of soluble and insoluble protein in the flour using a machine called the Glucomatic. Protein plays a big role in the wheat market and high-gluten wheat is always more expensive. However protein isn't measured in the same way around the world. In the US for instance, the percentage of protein is determined based on a 14% moisture content while in France the moisture is removed before testing and 100% dry matter is used. In other words, a 11.5% protein flour in the US would contain less than 10% protein if measured the French way. For the purpose of artisan baking, a flour made from low-protein hard wheat is best because of its high tolerance to long fermentation while industrial bakers - who make mostly pan breads and want to develop the gluten to the maximum in order to get a tight crumb - favor protein-rich hard spring wheat. Hard winter wheat spends more time in the ground which boosts the quality of the protein by making it very resistant to protease, an enzyme whose role is to break down protein. What role do proteins play in bread making? Water-soluble proteins participate in enzymatic activity and contribute to the nutritional value of the bread. Water-insoluble proteins form the gluten network, giving the dough its elasticity, extensibility and tenacity. Rye contains less protein than wheat (8 to 12 % as opposed to 10 to 14%) and a large part (30 to 50%) of this protein is water-soluble, which means that it doesn't help form a gluten network. However this can be partially compensated by using lowering the pH of the dough (using an acidic agent such as a sourdough starter). More about rye in a future post. Stay tuned!

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  2. Hi MC

    This is a very good write-up. I have completely forgotten about that part of the teaching at Artisan III. Thank you.
    Your explanation was very clear. However, I had problems conceptualizing the bit about protein levels in different flours. If, as Didier said, the protein is measured on a flour which has 14% in moisture as in the case of the US flour, that would mean that the protein is only based on the remaining 86% of the flour; ie, the dry matter. For the sake of argument, if the 14% is also “dry matter,” there would be more protein. And therefore, what is quoted as the figure for protein in the US should be higher in the French way of measurement.

    In my way of thinking, the example that Didier gave (ie, that “… a 11.5% protein flour in the US would contain less than 10% protein if measured the French way.”) should be just the other way around. That is, an 11.5% protein flour in the US should contain –

    11.5% divided by 0.86% = 13.37% protein in the French measurement.

    Do you have Prof. Raymond Calvel’s book? On page 4, (Chapter 1, Flour) there is a table which lists the difference in protein and ash contents in the US and France. And, indeed, 11.5% protein in the US 14% moisture flour is equivalent to 13.69% in France!! (Note: my calculation above is only a simple arithmetic calculation based on the logics behind.)

    It is the same thing with regard to ash content. For example, 0.52% ash content in the US measurement is equivalent to 0.62% in the French measurement. That is because the US figure of 0.52% is based on 86% dry matter (because 14% is taken up by moisture).

    Shiao-Ping

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