Bailey gives three equations which represent the reactions that may take place under favorable conditions. He adds that equation (3) represents what probably usually occurs.

sodium acid pyrophosphate

With sodium acid pyrophosphate Bailey states that there is some question concerning the products of reaction and gives two equations that may represent what occurs.

and

And

Sodium acid pyrophosphate

Sodium acid pyrophosphate is at present put up with cornstarch and sold only to bakers. The bakers add the soda, using 2 parts of combined starch and disodium pyrophosphate to 1 part of soda. This proportion yields about 17 per cent of available carbon dioxide. Some of the other baking powders for the bakery trade are also made to yield 17 per cent of carbon dioxide.

Sulfate powders. The author knows of no straight sulfate powders on the market at the present time. Sodium aluminum sulfate is the acid salt used in these powders.

Combination sulfate-phosphate powders. These powders contain two acid salts in varying proportions. The sulfate salt is sodium aluminum sulfate and the phosphate is monocalcium phosphate. Hart states that sodium aluminum sulfate "has first class keeping quality and has an aerating value about the same as tartartic acid." The reaction of the phosphate salt with soda has been given above. One ingredient of the residue of sulfate powders is aluminum hydroxide. Another is sodium sulfate. The latter in excess produces a bitter taste. The sodium aluminum sulfate is first hydrolyzed with water. The sulfuric acid formed then reacts with the sodium bicarbonate. Bailey states that "Besides the reaction of the phosphate and sodium Na2SO4 A12(SO4)3 + 6H1O ---> Na2SO4 + 2A1(OH)3 + 3H1SO4 3H1SO4 + 6NaHCO3 ----> 6CO2 + 6H1O + 3Na2SO4 aluminum sulfate with soda, there is probably an interaction between the two.

The preceding Graphic Chart by Dr. Chittick shows "the ingredients present in the various types of baking powders, proportioned to produce 14 per cent of gas, which is the average strength of the standard baking powders." It also shows the compounds formed from the reaction of the various baking powders and the percentage or possible percentage of these compounds.

Chittick has suggested calling baking powders containing the sodium aluminum sulfate salt (sometimes known as aluminum or S.A.S. baking powder) sulfate powders, which is a good suggestion. He also suggests that baking powders consisting of a combination of sodium aluminum sulfate and phosphate salts be called sulfate-phosphate baking powder. These changes are shown in the Baking Powder Chart. Because of the number of times names of types of baking powder are used in the laboratory outline, the author has used the abbreviation, S.-P., for sulfate-phosphate powders.

Temperature and reaction of baking powder. Sulfate powder reacts slowly at room temperature. Bailey states that at room temperature a tartrate baking powder will react completely, a straight phosphate will yield two-thirds of its gas, but heat is required to liberate the remainder, and a combination powder will liberate from one-fifth to one-third of its gas. The baking powders that liberate a larger proportion of carbon dioxide at room temperature are often referred to as rapid acting; those liberating a small proportion at room temperature are called slow acting. Bailey classes sodium acid pyrophosphate as a slow-acting powder. Barackman states that it may be classed as a rapid-acting powder in water but a slow one in a dough. Sulfate-phosphate is a combination of a rapid- and a slow-acting powder. It can be readily seen that it is possible for some types of powder to lose a larger proportion of gas during mixing than other types of powder. For this reason a smaller amount of the slow-acting powders can be used in many baked products.

Batters And Doughs Part 3 94

Fig. 45. - Showing the proportion of ingredients in baking powders to yield 14 per cent of carbon dioxide. In the first square at the bottom of the columns is listed the type of baking powder. Next come soda and cornstarch, which are common ingredients in all powders. In the fourth squares are the acid ingredients and the percentage required to yield 14 per cent of carbon dioxide. The next to the last squares at the top give the residues from the reaction of the baking powder ingredients; those on the left of the center of each diagram are soluble and those to the right are insoluble in water.

Courtesy of Dr. Chittick and Jaques Manufacturing Company.

The amount of carbon dioxide lost from a batter. A smaller proportion of gas is lost from a batter during mixing than from water, owing at least in part to the density and viscosity of the dough mixture. Noble and Halliday have done considerable work with baking powder. The following table from their results shows the comparative loss from water and from a simplified dough mixture after mixing for 40 seconds. They have also determined the amount of carbon dioxide evolved in a simplified batter during 40 seconds' mixing. This was only slightly greater than the amount lost from the batter, as shown in Table 53.

Carbon Dioxide Lost When Baking Powder Is Combined with Water Only, and with Other Ingredients into Batters (Noble and Halliday)

Average quantity of CO2 lost when baking powder is mixed for 40 seconds with

Type of baking powder

Water

Flour, fat, water

Flour, fat, milk

Flour, fat, sugar, and water

Average quantity of CO2 lost when baking powder is beaten for 20 sec-onds with flour, fat, and water

4.9 per cent sugar

9.8 per cent sugar

per cent by weight

per cent by weight

per cent by weight

per cent by weight

per cent by weight

per cent by weight

Tartrate

10.11

6.77

6.01

6.45

6.78

6.18

Phosphate

9.34

5.56

....

4.71

5.81

4.52

S. - P. 1

5.15

3.25

2.78

2.58

2.60

2.70

S. - P. 2

3.91

2.29

1.76

1.89

2.61

1.27

Barackman states that far baking purposes the carbon dioxide from baking powder may be divided into three divisions as follows: "1. the amount lost from a dough during mixing and standing; 2. the amount causing expansion of the dough; this is called 'bench action' by bakers; 3. the amount of carbon dioxide dissolved and adsorbed and that available from unreacted soda which will be effective as leavening at oven heat." Barack-man has determined the carbon dioxide for these three divisions in biscuits and doughnuts. Instead of using baking powder he used acid salts and soda in the dough mixtures. The acid salts used were calcium acid phosphate, sodium acid pyrophosphate, potassium acid tartrate (cream of tartar), and sulfate-phosphate. For convenience dry mixes were made up to which water was later added in a special mixing apparatus. The dry mix for biscuits contained flour, soda 1.5 per cent (flour basis), acid salt, and shortening 10 per cent. The dry doughnut mixture contained flour, soda, acid salt, shortening 5.55 per cent, sugar 22.2 per cent, powdered egg 3.33 per cent, and dry skim milk 10 per cent. When water was mixed with the dry ingredients heat was evolved. This made it necessary to use control doughs containing no acid salt or soda, to correct for the expansion of occluded air in the dough. The doughs all had a final temperature of 27°C. = 0.5°.