Yeasts are a group of single-celled fungi and about 160 different species are known in yeast varieties. It is one species in particular, Saccharomyces cerevisiae or "brewer's sugar fungus," that is good for brewing and baking.
Yeast gives off a characteristic flavor and smell. It leavens bread and converts the grain carbohydrates into alcohol and carbon dioxide. When we buy yeast, it is live but inactive. With a little warmth and the addition of some water, it is activated and it releases the gas, carbon dioxide, that will raise the dough. The activity ceases only when the dough is placed in the oven and the yeast is killed by extreme heat.
Fresh yeast (cake/compressed yeast). This should be putty like in color and texture. It should look firm and moist and feel cool to the touch. If it is dry, dark and crumbly, it may be stale or not live. Fresh yeast can be bought for a pittance from many supermarkets that have a bakery on site or from your local bakery. Keep fresh yeast in an airtight container in the fridge for up to 3 days. Alternatively, divide the yeast into 1/2-ounce or 1-ounce portions and freeze for up to 3 months. Always defrost it thoroughly at room temperature or in the fridge before use.
To use: Using a spoon, crumble the fresh yeast into a small glass bowl and add about a quarter of the required amount of water as specified in the recipe you're using. Use the back of the spoon to cream the yeast until it dissolves in the water and forms a smooth blended paste. Stir in the remaining water. The yeast mixture is now ready to be added to the flour.
Active dry yeast. Usually bought in jars of packets from the supermarket. Active dry yeast can be reconstituted with a little lukewarm water and will give exactly the same result as fresh yeast. It must be stored in an airtight container and always keep an eye on the expiration date. If it doesn't produce a frothy head when reconstituted with water, it is not fresh.
To use, sprinkle active dry yeast into a small glass bowl containing the quantity of lukewarm water as specified in the recipe. Leave to dissolve for five to ten minutes. Once the yeast has dissolved, stir the mixture with a wooden spoon. The yeast mixture is now ready to be added to the flour. Continue as instructed in the recipe.
Rapid Rise Yeast. The easiest of yeasts to use as it is just added to the flour, with the water added separately. Again, the end product will be just as superior as using fresh or granular yeast. Always check the date stamp to ensure freshness.
To use, sprinkle rapid-rise yeast directly onto the flour. The yeast will activate once they liquid has been added. Continue as instructed in the recipe. Rapid-rise yeast cannot be used for the “sponge” method.
Note: 1/-ounce (15g) fresh yeast equals 2 teaspoons active dry yeast equals 2 teaspoons dried rapid-rise yeast.
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