BITTER YEAST.—­It sometimes happens that an excessive use of hops in the making of yeast gives to it so bitter a flavor as to communicate a disagreeable taste to the bread.  To correct this bitterness, mix with the yeast a considerable quantity of water, and let it stand for some hours, when the thickest portion will have settled at the bottom.  The water, which will have extracted much of the bitterness, can then be turned off and thrown away.  Yeast also sometimes becomes a bitter from long keeping.  Freshly burnt charcoal thrown into the yeast is said to absorb the odors and offensive matter and render the yeast more sweet; however, we do not recommend the use of any yeast so stale as to need sweetening or purifying.  Yeast that is new and fresh is always best; old and stale yeast, even though it may still possess the property of raising the dough, will give an unpleasant taste to the bread, and is much less wholesome.

TESTS FOR YEAST.—­Liquid yeast, when good, is light in color and looks foamy and effervescent; it has a pungent odor somewhat similar to weak ammonia, and if tasted will have a sharp, biting flavor.  Yeast is poor when it looks dull and watery, and has a sour odor.  Compressed yeast, if good, breaks off dry and looks white; if poor, it appears moist and stringy.

If there is any question as to the quality of yeast, it is always best to test it before use by adding a little flour to a small quantity and setting it in a warm place.  If it begins to ferment in the course of fifteen or twenty minutes, it is good.

STARTING THE BREAD.—­Having secured good yeast, it is necessary in some way to diffuse it through the bread material so that it will set up an active fermentation, which, by the evolution of gas, will render the whole mass light and porous.  As fermentation is more sure, more rapid, and requires less yeast to start it when set in action in a thin mixture than when introduced into stiff dough, the more common method of starting fermented bread is by “setting a sponge;” viz., preparing a batter of flour and liquid, to which potato is sometimes added, and into which the yeast is introduced.  Some cooks, in making the batter, use the whole amount of liquid needed for the bread, and as the sponge rises, add flour in small quantities, beating it back, and allowing it to rise a second, third, or even fourth time, until sufficient flour has been added to knead; others use only half the liquid in preparing the sponge, and when it has well risen, prepare a second one by adding the remainder of the liquid and fresh flour, in which case the fermented batter acts as a double portion of yeast and raises the second sponge very quickly.  The requisite amount of flour is then added, the dough kneaded, and the whole allowed to rise a third time in the loaf.  Other cooks dispense altogether with the sponge, adding to the liquid at first the requisite amount of flour, kneading it thoroughly and allowing it to rise once in mass and again after molding into loaves.  As to the superiority of one method over another, much depends upon their adaptability to the time and convenience of the user; light bread can be produced by either method.  Less yeast but more time will be required when the bread is started with a sponge.  The end to be attained by all is a complete and equal diffusion of gas bubbles generated during fermentation throughout the whole mass of dough.