Use 1/2 teaspoon yeast per cup of flour in normal cycle machines. The amount may be 2-3 times more for one-hour or express machines. Only 3/4 teaspoon of active dry yeast per cup of flour can be substituted for the standard cycle. In certain brands, quick yeast and bread machine yeast can be used interchangeably in recipes. For best results, follow the brand's instructions for your type of yeast. Yeast is a fungus that causes grains to rise when mixed with water and allowed to sit until mold forms on the surface. Yeast is available as compressed cakes or as liquid yeast. Both have their advantages. Compressed yeast is easy to store and use; it will keep for several months if stored in an airtight container. Liquid yeast is less stable but can be easier to measure. Both types of yeast can be used to make bread. Too much or too little yeast can cause your bread to fail to rise properly. There are two ways to ensure you add the correct amount of yeast to your dough: by weight or by volume. To calculate by weight, divide the amount of yeast by the number of grams of sugar (for example, 1/2 ounce [15 grams] of yeast divided by 11 ounces [320 grams] of sugar equals 0.135 ounces [4 milliliters]). To calculate by volume, multiply the amount of yeast by 31/2 teaspoons (5 ml) and then divide this number by 110 (the density of sugar).