Salt In Bread Dough

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Salt In Bread Dough

http://www.paperthetown.com/bread/b172.html

Recipe By :"Maggie Glezer"

Serving Size : 1 Preparation Time :0:00

Categories : Bread-Bakers Mailing List Miscellaneous & Tips

(Originally published in the Bread Bakers Guild of America Newsletter)

Salt is such a minor ingredient in bread that few bakers stop to think about its exact role in bread-making. However, sometimes focusing a light on a seemingly unimportant aspect of bread-making can illuminate the whole bread-making process. Such is the case with salt. Salt exerts an influence on almost every stage of bread-making, and every aspect of bread. Why is salt one of bread's cornerstones? What importance does it have beyond being a flavoring element? This article will attempt to explain and clarify some of the chemistry governing salt's interactions with bread dough.

Salt's primary purpose in bread is to evoke and enhance the bread's flavor. To most Americans, saltless bread is insipid and virtually inedible, but adding only approximately 2% of the flour weight in salt to the average bread formula manifestly changes the perception of bread's flavor, eliciting the full spectrum of complex flavor notes, including a sweetness that would be otherwise absent. It is interesting that the addition of salt to bread is a relatively new preference. Medieval bread was almost never salted because salt was very expensive and difficult to procure; thus, salt-less bread was preferred. According to Professor Raymond Calvel, professor emeritus of l'Ecole Francaise de Meunerie, French bread formulas started to include salt only at the end of the eighteenth century.

Besides flavoring the bread, bakers have long noted salt's alteration of certain dough characteristics. Unsalted dough mixes faster, has little resistance to extension and feels sticky. Bakers who delay the salt addition during mixing find that once salt is added, the dough tightens, becoming more difficult to stretch, but also becomes stronger, and is thus capable of stretching farther without ripping. (Testing by cereal scientists confirms this seemingly contradictory observation: salted doughs are both more resistant to extension and more extensible once deformed.) During fermentation, salted doughs rise more slowly, an occurrence usually solely attributed to salt's dehydrating effect on yeast. To understand how salt affects these changes, and to see if our assumptions hold true, we will need to take a look at the interactions within the dough on a molecular level.

Table salt is a type of crystal made up of chlorine and sodium ions, or charged atoms. In its crystalline state, salt's ions are positioned in a stable, geometric lattice. However, when mixed with an appropriate solvent such as water, salt dissolves, meaning that the ion lattice is forced apart by the solvent and the individual ions become enveloped by the solvent. This is exactly what occurs in a dough: crystalline salt is quickly dissolved by the dough's liquid into sodium and chloride ions.

The presence of any type of dissolved material, including ions, in the dough's liquid phase affects the function of the yeast and lactobacilli living in the dough (all doughs, not just sourdoughs, contain acidifying bacteria which contribute to the bread's flavor). In an unsalted dough, water will move freely into the yeast or bacteria cell. However, if salt is added to the dough, osmotic pressure, determined by the amount of material dissolved in the dough's liquid, will increase, drawing out some of the cell's water and thus partially dehydrating it. Higher osmotic pressure also limits the amount of fermentable sugars able to pass into the cell. These two effects--a loss of cell pressure and a decrease in sugars--combine to slow the overall rate of fermentation of both organisms. If the percentage of salt added to a dough becomes too high, excessive dehydration will eventually kill the yeast and bacteria.

Most scientists believe that at 2% of the flour weight or less, salt alone does not significantly alter either the yeast's gassing power or the bacteria's acid production. A study measuring the gas production in a fermenting dough has shown that gas production is retarded by only about 9% in a dough containing 1.5% salt (based on the flour weight).

Although salt's osmotic effect on fermentation reduction may be minor, it must be taken into consideration when attempting to maximize the build up of fermentation byproducts in pre-ferments. Thus, salt is always omitted in sponges, poolish, biga, and most other pre-ferments to ensure the greatest possible production of byproducts.

If the osmotic pressure exerted by the salt does not significantly change the fermentation rate of the dough, why does the dough rise so much more slowly when salt is added? This phenomenon can be attributed to salt's direct effect on the gluten protein network. Salt strengthens, tightens and compacts the gluten protein network, making it more resistant to pressure exerted by the build up of gaseous carbon dioxide. In salted doughs, gas production may be approximately equal to unsalted doughs, but, since the gluten protein network itself is less extensible, the dough is more resistant to the stress created by the internal gas buildup.

How does salt strengthen the gluten protein network? This is where the cereal science becomes murky. Although cereal chemists have been studying doughs for many years, there is still no real understanding of bread dough on a molecular level. Dr. O.K. Chung of the U.S.D.A. in Manhattan, Kansas, one of the leading experts on cereal lipids, has called the biochemistry of doughs "a huge puzzle," where every possible biochemical reaction is occurring at once, each one influencing the whole. In addition, every chemist has his or her own pet theories, none of which are strictly proven. So the layman must tread only where the path is well trampled.

The gluten in wheat is unique among the cereal proteins, because, when hydrated, it is capable of bonding with itself to form a viscoelastic web-like structure. "Viscoelastic" means that the web is both viscous and elastic: When a wheat dough is stretched out and released, it will either flow into a new configuration or retract back into its original shape. The gluten web can also trap and secure air bubbles, preventing them from migrating to the surface of the dough and releasing their gas. It is this last characteristic that allows a dough to be leavened by the carbon dioxide produced by the yeast.

The most widely-accepted current theory holds that the lower the dough's pH, the more positively-charged the gluten structure will be. A typical dough has a pH low enough (approximately 5) for the gluten protein to carry some positive charge. Because like charges repulse, the protein filaments in a typical dough repulse one another, resulting in a more loosely organized and less interconnected web. When salt is added to a dough, some of the negatively-charged chlorine ions will bond with the positively-charged sites on the gluten protein, neutralizing the overall charge. With the repulsive forces eliminated, the web will tighten, compact, and bond with itself more strongly. A more bonded, compact gluten web can better withstand the force exerted by the swelling air bubbles in an actively fermenting dough, and thus will expand more slowly.

Thus, while salt does slow the dough's expansion during fermentation, the long held belief that salt retards the yeast's gas production has been shown to be of only minor consequence to the fermentation rate. Instead, the primarily cause of the slow down has been shown to be a tightening of the dough's gluten structure, induced by salt's neutralization of the structure's charge. It still remains to be seen how this alteration of the dough's backbone affects its formation during mixing, or how a modification of the gluten impacts other dough constituents, especially the dough's lipids (fats) and enzymes.

Although the explanations in this article have been greatly simplified, hopefully the reader has come away with some insight into the chemistry of bread dough, and now has a heightened appreciation of the complexity surrounding even the most prosaic ingredients.