This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
(Swanson and Working)
Total time of me-chanical treatment 60 r.p.m., minutes
Total time of fermen-tation, minutes
Volume of loaf, cc.
Manipulation of dough. In the laboratory in experimental cookery, one is constantly impressed by the effect of manipulation and the handling of the food materials in giving results that are not strictly uniform.
Swanson states that it is well known that bread dough must not be squeezed too hard when kneaded just before it is put in the pan, or the cell walls will be thickened. He gives as the reason that during the fermentation the meshwork of gluten has become separated into fine filaments. If kneaded too hard just before being put in the pan these filaments are packed together and as a result a thicker cell wall is produced.
The experiments of Dunlap are of particular interest. At the Bureau of Chemistry in Washington, he and two other operators mixed dough. The only difference in the mixing was the way the dough was kneaded or punched after the first mixing by the different operators. Dunlap's description follows. "In these experiments the three operators used identical formulas and ingredients in preparing the dough batches. The mixers were all started at the same time, the water and shortening were added at the identical instant, and the extent of the mixing was absolutely uniform. All fermentations were carried out in the same cabinet and at the same time and for the same period. All punches were synchronous and the working or punching of the dough was uniform, that is, the doughs were worked or punched with the hand 40 times after the first rise and 30 times after the second. The doughs went to the same proofing cabinet and at the same time. In fact uniformity so far as was humanly possible prevailed throughout. When the bakes came from the oven, the results were very illuminating for despite the care taken, they were far from uniform." These experiments were repeated several times with the same results.
In later experiments carried on in another laboratory, Dunlap decided he had punished the dough too hard or used too much pressure in punching it, especially for the last working. He states, "Putting this idea to the test and handling the doughs with a degree of gentleness previously unknown in my method of operation, results were produced incomparably better than anything previously obtained."
Applying these results it can be stated that the first mixing and kneading, when the gluten is developed, should be thorough, but may not need heavy pressure, and the second and third kneading should be done with light pressure and should not be continued for too long a period.
The mixing of the bread in the bowl should be continued until the dough forms in a ball and cleans the side of the bowl. If a bread mixer is used it may mix and knead at the same time.
For the first kneading, only a thin film of flour should be used on the board, unless far too much liquid has been added. Inexperienced bread makers usually add too much flour in kneading, for in mixing by hand the dough should be sticky when kneading is begun. After the gluten is developed it no longer sticks to the hands or board. In molding, use very little or preferably no flour, for flour added at this stage may produce streaks in the bread, since this flour is not fermented for the whole period.
Greasing of bowl and pans. The bowl that the dough is allowed to rise in should have only a thin film of fat to grease the bowl, or it is not necessary to use any. Heavy greasing may produce streaks in the bread. Harrel found that bread baked in ungreased pans gave a better volume and oven spring than bread baked in greased pans. This indicates that the dough clings to the sides of the pan during rising, and this adhesion aids in attaining a better volume. But greasing the bottom of the pan expedites removal of the bread.
Fermentation. The production of gas in the dough to render the bread porous is known as fermentation. Both yeast and bacteria are used to produce gas, bacteria producing the gas in salt-rising bread, yeast in ordinary bread.
Microorganisms in breadmaking. Fuller states that the "microorganisms associated with the production of bread may be divided into three main groups: (1) the yeast Saccharomyces cerevisiae, carefully purified and selected strains of which are purposely added to the dough; (2) certain bacteria, which, introduced either purposely or accidentally, assist in the development of the gluten and give rise to characteristic flavoring products; and (3) the unwanted organisms, B. mesentericus, torulae, and moulds, which are introduced chiefly from flour, air, and perhaps water, unintentionally either into the dough or onto the baked loaf."
Fuller states that it seems likely that attention has been confined too much to selecting and purifying yeasts in relation to their carbon dioxide producing powers and that side reactions, i.e., bacteria-producing, essential flavoring ingredients have been neglected. He cites the work of a Russian microbiologist who examined the bacterial flora of a number of samples of "leaven." The dominant organism in all was Lactobacillus panis acidi, with Streptococcus lactis acidi and others in small numbers. Adding Lactobacillus panis acidi to yeast gave a bread with flavor superior to that of bread in which yeast alone was used.
Enzyme action in fermentation. The yeast contains an enzyme, zymase, that produces carbon dioxide and alcohol from the sugar. During fermentation many changes are occurring in the dough. The flour enzymes as well as the yeast enzymes bring about definite reactions. The chief amylolytic enzyme of the flour, diastase, produces maltose from starch. Flour contains some initial sugar but this is used up in gas production and it is essential for sugar to be formed for new gas production. Yeast also contains some diastase. Sugar is usually added to bread dough. It is not essential, but fermentation is more rapid. Most flours contain sufficient diastase for bread making, but in some the diastatic activity is weak. Commercial bakers may add diastase preparations to dough made of flours weak in diastase to shorten the fermentation time.
Sugar is often added in rather large quantities in home-made bread and it, plus the sugars already present in the flour, plus the sugar formed by the diastase during fermentation, furnish the sugar for the action of the zymase to produce carbon dioxide.
The proteinases hydrolize a part of the protein, and if very active may cause harmful results. For, if the gluten, which during the first part of fermentation may be too tenacious, becomes too soft or thin the volume of the loaf may be diminished and the texture impaired. Balls and Hale say a little proteinase is beneficial. J orgensen states that yeast water stimulates the activity of proteinase.
"Bread improvers." Many and various substances have been suggested and tried as so-called "bread improvers." Malt preparations containing both diastase and proteinase are sometimes added to dough. They are of greater benefit if added to flours low in natural diastase. The rate of diastatic activity may depend upon the relative percentage of starch which is embedded in gluten, the size of the starch granules, and other factors. With many granules embedded in gluten the diastase has less surface on which to act. If the starch granules are smaller there is a relatively greater area for the action of the diastase. However, Markley and Bailey in their investigations found particle size did not determine diastatic activity, but that the rate was affected by humidity of the granule surface, possibly because the granule wall is less resistant.
At present potassium bromate is commonly added to bread dough by commercial bakers. J orgensen states that it imparts a beneficial action because it diminishes the action of the proteinase. Balls and Hale attribute part of the improvement of bleaching and aging of flour to diminution of proteinase activity. J orgensen has applied for a patent in the United States for using ascorbic acid as a bread improver, its beneficial effects being attributed to its ability to depress plant-proteinases of the papain-type.
Imbibition of water during fermentation. Sharp and Gortner have found that during yeast fermentation the imbibition of water increases to a maximum and then decreases. The increased imbibition during fermentation is due to the increase in the hydration capacity of the glutenin. During fermentation the acidity increases, but Johnson and Bailey have reported that the acids of fermentation cannot alone produce all the changes that occur during fermentation. The proteolytic enzymes by hydrolyzing a part of the protein aid in softening of the gluten. Swanson and Working have suggested that the mechanical action of the expanding gas by stretching the gluten also aids in bringing about a modification of the gluten.
Dispersion of gluten during fermentation. Johnson and Bailey in studying the effect of hydrogen-ion concentration on dispersion of the gluten of the flour found that as the acidity increased the percentage of proteins dispersed or the protein in the aqueous extract of the fermented dough increased. It is either very difficult or impossible to collect the gluten from a dough that has fermented sufficiently for baking, by washing it in water. This in itself shows a change in the condition of the gluten.
Johnson and Bailey have reported the following amount of protein dispersed, or in the aqueous extract, during fermentation of a soft-wheat dough, without added salt. At an optimum pH for baking the bread, more than half the protein was in a dispersed phase.
Desirable acidity for bread. As fermentation of the dough progresses its acidity is increased. Johnson has reported that some lactic and acetic acids are formed during fermentation. Bailey and Sherwood have shown that in bread dough the increased acidity is largely due to carbon dioxide. The pH of the baked bread is always higher than that of the dough from which it is baked. For an average gluten a pH of about 5 is desirable. With all doughs, if the fermentation is carried too far the volume of the bread is poor and it has a sour odor and flavor. The following table is from Bailey and Sherwood.