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Yeast is a single-celled fungus (a living organism) that exists in many forms. It converts sugar and starch into carbon dioxide bubbles and alcohol, which makes it useful in the production of bread, beer, and wine. In the context of baking, it produces carbon dioxide when mixed with warm water, flour, salt and/or sugar, which causes the dough to expand resulting in a soft and spongy product.
There are many varieties of yeast:
• Active Dry/Rapid Rise/Bread Machine - These are often referred to as ‘baker's yeast’. Active Dry is the most commonly used variety and is recommended for hand-kneaded dough. It is available in 1/4-ounce, 3-strip packets and 4-ounce jars.Rapid Rise and Bread Machine yeasts are fine-grained. They cause a single-rise reaction, which makes them more efficient in machined dough. Rapid Rise is sold in 3-strip packets and Bread Machine yeast is sold in 4-ounce jars.
• Cake Yeast/Fresh Active –These are foil-wrapped, compressed square cakes. They are commonly available in two sizes: 2 ounce and .06 ounce. They cannot be used in bread machines, but are typically used by commercial bakers.
• Wild Yeast - This is the ‘starter’ that many cooks keep alive in a crock. Each week, 75% of the starter is replaced with water and flour to keep it growing. The live yeast that is removed is used for baking, or discarded. Most artisan breads are made from wild yeast. However, starter or sponges are not as reliable as packaged or cake yeasts.
Yeast for bread-making can be fresh, dried or 'easy-blend', but in all cases remember that it is a living organism that needs moisture, warmth and food (such as sugar or flour) to grow. Yeast should be dissolved in warm water (100-110 degrees F) only and never hot water because extreme heat kills the yeast – that is why the dough stops rising when it's baked in a hot oven. Sugar is usually added to ‘feed’ and grow the yeast.
Once you provide the required warmth and food, you should see activity within 5 minutes. There will be bubbling and expansion during yeast activation. If you see no activity, your yeast may be too old, or the water might have been hot or cold. As yeast grows, it produces carbon dioxide, which makes the dough expand and rise. In general, slowly risen dough results in bread with superior flavour and texture.
You should never eat raw active yeast, since it will continue to grow in your intestine and rob your body of valuable nutrients. But once deactivated through pasteurization, yeast is a good source of nutrients.
How to Select
• Dry yeast is readily available in markets.
• It comes in envelopes, jars or bulk.
• It may be regular or quick rising.
• Quick rising will take only half the time for rising.
• Please note that when buying yeast, the date of expiry should be strictly followed.
• Fresh yeast is very perishable and it recommended only for experts – it will last only for one week.
• Bread is made with baker's yeast, which creates lots of bubbles that become trapped in the dough, causing the bread to rise and become light and airy when baked.
• A small amount of alcohol is also produced, but this burns off as the bread bakes.
• Beer yeast and wine yeast are used to convert sugar into alcohol and, in the case of beer and champagne, bubbles too.
How to Store
• Always store in a cool, dry place, preferably the refrigerator (a must for fresh yeast), but bring to room temperature before using.
• Fresh yeast is extremely perishable and should be used within 1-2 weeks or date on package.