Yeast 酵母

As mentioned before, we will elaborate on the major ingredients in bread-making. Today we want to introduce to you the first on the list: yeast.

Yeasts are organisms that feed on sugar/starch, and gives off carbon dioxide, alcohol, and water. They work optimally at warmer environments with moisture and oxygen present. There are various kinds of yeast, but the two major kinds of yeast you can find in almost any supermarkets are a) active dry yeast, and b) instant dry yeast. These two kinds of yeast are both dried, milled into granules, and packaged sometimes in sachets (each holds approximately 7 grams which is equivalent to 2 1/4 teaspoons), bags, cans, or plastic containers. Dried yeasts stay dormant until lukewarm water is added. Active dry yeast has a larger granule, and needs to be dissolved in water before using, while instant dry yeast is finer, and can be incorporated straight into other ingredients. These can be used interchangeably, but if the yeast has been sitting on your shelf or your fridge for some time, do test out the viability of the yeast before incorporating it in other ingredients. You can do that by dissolving a small amount of yeast and a sprinkle of sugar in lukewarm water. The temperature of water matters as yeasts are sensitive to water temperature. You will be killing the yeast if the water is too hot. But if it’s too cold the yeast will not be activated. The ideal temperature is roughly 110°F, that is 43°C. For your reference, our body temperature is at 37.4°C, therefore if you do not own a food thermometer, you can test the water by immersing your fingers into a bowl of lukewarm water. If your fingers can stand the heat for more than 10 seconds, the temperature is about right. Give the yeast 5 minutes to work. If it puffs and foams and gives off a yeasty smell, the yeast is good to go. If nothing happens, discard the yeast and buy a new batch. To make a loaf or two of bread, a sachet of yeast is sufficient. When yeast is mixed with flour, salt, warm water, it is kneaded until a smooth dough is formed. The dough is usually left to sit covered on the counter or in a bowl until it has doubled in size. The dough is then shaped into loaves and left to rise again until it has doubled again. What happens during the rise is that yeasts digested the sugar from the flour and form pockets of carbon dioxide that gets trapped by the gluten structure generated by kneading wheat flour into a dough. When the dough is baked, the pockets are set, producing a soft and spongy structure throughout. The time for each rise depends on the humidity and temperature, but on average each rise takes approximately 45 minutes to an hour. But during this time you do not have to stand there and observe the yeast, you are free to do other chores while the yeasts are working its magic.