The proportion of flour in muffins is usually 2 cups to a cup of liquid. For this reason, the extent of mixing has more effect on the structure of the batter and the finished muffins than in thin batters. The gluten with this proportion of liquid is more sticky and glue-like than in the thinner batters. It can be attenuated. Melted fat or an oil is distributed in an uncooked muffin batter in the same manner as in griddle cakes.

Effect of extent of mixing on texture and appearance. With just enough mixing to barely blend the ingredients, 30 strokes or less, the batter breaks and separates easily when lifted with the spoon, is lumpy and not smooth in appearance. The top of the baked muffin is rough, though it browns well and is a little shiny and has a glaze. The volume of the muffins is good, its cells rather large and uniform in size, and its cell walls of medium thickness. The muffin is tender. This amount of mixing, usually about 25 strokes, which can be partially determined by the appearance of the batter, is the optimum amount of mixing. It is the amount that is required to just blend the dry flour with the liquid ingredients. See Figs. 46 to 48, muffins number 1.

When the mixing of the batter is continued beyond the optimum amount, the appearance of the batter gradually changes, becoming smoother and less lumpy. It flows more readily, and as it falls from the spoon it tends to cling to the spoon, forming long ribbon-like strands. The muffins also change in appearance, texture, and volume with longer mixing. See muffins 2 and 3, Figs. 46 to 48. The top of the muffin is less rounded and may come to a sharp point or peak. Its crust is smoother, browns less readily, and becomes duller in appearance with less glaze. Up through the center of the muffin are found long holes, which are called tunnels, that end just below the point at the top. Large holes are often found in muffins and cakes, caused by addition of air in mixing, but tunnels are long and rather narrow. When tunnels develop the muffins are less tender. The grain of the muffin becomes finer with longer mixing, the cell walls thinner, the tunnels more numerous, and the muffin is more compact. With extremely long mixing, and particularly with phosphate or tartrate baking powders, the texture of the muffin may be very soggy, the volume small, with few tunnels, the top flat and very smooth in appearance. See muffins 4, Figs. 46 to 48.

Tunnels. Tunnels usually start at the bottom of the muffin and converge near the center at the top. They are formed from expansion of gas in the dough. Part of this gas is from steam, for if one watches the baking of muffins through a glass oven door, occasional small jets of steam may be seen to escape from muffins that have been stirred sufficiently so that tunnels develop. With thin batters like popovers, or doughs like baking powder biscuits, tunnels do not develop. When the batter contains the

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Fig. 46. - Muffins. Showing effect on texture, volume, and shape when the extent of mixing is varied and a tartrate baking powder is used. Experiment (82,A,1). Approximately 1/8 of the batter, 60 grams removed after mixing,

1. 30 strokes.

2. 60 strokes.

3. 100 strokes.

4. 300 strokes.

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Fig. 47. - Muffins. Showing the effect on texture, volume, and shape when the extent of mixing is varied and a phosphate baking powder is used. Experiment (82,A,2).

Approximately 1/8 of the batter, 60 grams removed after mixing,

1. 30 strokes.

2. 60 strokes.

3. 100 strokes.

4. 300 strokes.

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Fig. 48. - Muffins. Showing the effect on texture, volume and shape when the extent of mixing is varied and a sulfate-phosphate baking powder is used. Experiment (82,A,3).

Approximately 1/8% of the batter, 60 grams removed after mixing,

1. 30 strokes.

2. 60 strokes.

3. 100 strokes.

4. 300 strokes.

Proportion of water that results in a very sticky gluten, and the gluten is attenuated to the point at which it is tenacious and somewhat elastic like rubber, the batter drips from the spoon into the muffin pan somewhat as shown in Fig. 50 at A. The gluten strands of the batter are stretched toward the point in contact with the spoon. The manner or direction in which the tunnels form is partially dependent upon the way in which the gluten strands are stretched in mixing and in placing the batter in the pans. In the baked muffins the tunnels may form as shown in the cross-section diagram at B. When the batter from the end of the spoon falls near the edge of the muffin pan the tunnels may converge as shown in C, Fig. 50.

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Fig. 49. - Muffins. Showing the effect of stirring the batter 85 strokes; then adding the baking powder and stirring 15 additional strokes. Compare with muffins (3) in Figs. 46 to 48 mixed with 100 strokes.

1. Tartrate baking powder.

2. Phosphate baking powder.

3. Sulfate-phosphate baking powder.

Two other factors that influence the formation of tunnels, though their effect is not always consistent, are depth of the batter and the baking temperature. When the batter is mixed just to the verge of tunnel formation, the deeper the batter in the pan the more apt are tunnels to appear. The effect of temperature is still more variable than some of the other factors, but tunnels have been observed in portions of a batter baked at higher temperatures, when other portions baked at lower temperatures did not have them or they were less numerous.

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Fig. 50. - A. Cross section of muffin batter that has been mixed until the gluten is well developed, being dropped from a spoon into a muffin pan.

B. Direction of tunnels in baked muffin.

C. Direction of tunnels when the point of dough falls to one side of the pan.

Varying the proportion of ingredients in muffins. Too large a proportion of flour or too little liquid increases the tendency to form tunnels, even with a small amount of mixing. If sugar and fat are increased the gluten develops less readily, but the effect is not very great. The omission of egg does not change the muffin structure to a very great extent, although there is less tendency for tunnels to form. The flavor of course is different if the batter contains no egg. Increasing the egg tends to give a tougher, more rubbery, elastic muffin. Egg not beaten sufficiently to blend easily with other ingredients or not mixed sufficiently with the liquid may produce a rather waxy texture with fairly thick cell walls. This texture is often seen in muffins which are not over-mixed.

Baking powder. The electrolyte baking powder influences the viscosity and tenacity of the batter. When a muffin batter that contains no baking powder is just mixed, it separates from the spoon without forming strands and may be described as short. With longer mixing the batter becomes smoother, but there is not as definite a change as when the baking powder is in the batter during mixing. If the baking powder is in the batter during all the mixing period the batter is short when just mixed, but after the baking powder has dissolved, the batter seems more tenacious, and compact with longer mixing. That the volume is less is readily seen by the weight, for 60 grams of the batter is greatest after just mixing and becomes less with longer mixing. This is more noticeable with the phosphate or tartrate baking powders than with the sulfate-phosphate ones.

Fig. 49 shows muffins that have been stirred 85 strokes. Then the baking powder was added and stirred an additional 15 strokes. The knob-like protuberances are characteristic of muffin batter that has been mixed too long. The tartrate and phosphate powders, probably because of their more rapid action at room temperature, are less likely to develop these knobs. However, the sulfate-phosphate powders with over-mixing are more likely to develop these knobs, for less carbon dioxide is lost during mixing, hence more pressure is exerted during the baking.

The amount of mixing required for the best texture in muffins, with the different types of baking powders, is about the same, for the batter can be mixed only about 25 strokes or a little more with either a rapid- or a slow-acting powder.

All the muffins in the illustrations contained the same weight of batter, and were baked in pans of the same size. Thus the effect of mixing on the volume is shown by the comparative size of the picture.

Baking temperatures for muffins. A temperature of 195° to 210°C. is good to use for muffins. A very high temperature sets the crust before the batter has time to rise; a very low temperature requires a long time to brown and cook the muffins.

Greasing the sides of the muffin pans lightly or not at all aids expansion of the dough in baking, as the dough can cling more tenaciously to the sides of the tin; but greasing the bottom of the pan heavily expedites the removal of the muffins from the tin.

Standing before baking. All muffins and nut breads made with baking powder, but particularly those made with rapid-acting powders, should be mixed quickly and put into the muffin tins as quickly as possible after mixing. This lessens the amount of gas lost. They can stand in the muffin tins for some time before baking, because the dough is stiff and viscous and, if not cut across or through, most of the gas is retained.

The palatability of bran muffins can be improved by soaking the bran in warm milk before the flour and other ingredients are added, or the muffins may be allowed to stand for some time after mixing and before baking so that the cellulose of the bran becomes better hydrated and thus softer.