Yeast is a living organism. It needs food and moisture to thrive.
酵母是活性单细胞，无害，它仰赖食物（例如糖）和水份存活。
Yeast feeds on sugar and converts it into carbon dioxide through fermentation. Carbon dioxide is responsible for stretching and expanding the dough, something we see as the dough rises.
酵母喂了糖，会在发酵的过程种释放二氧化碳。二氧化碳在醒发面团的过程中，让面团能够具备伸展和扩张的能力。
Yeast fermentation also provides the flavor and texture.
发酵过程也会衍生出味道和质地。
Yeast will die in temperature 57°C or higher.
只要温度超过摄氏57度，酵母就无法存活。
Yeast is still effective in cooler temperatures, but it requires more time to expand the dough.
酵母激活了之后，即使面团被放到较冷的储藏室里，还是会继续扩张，只是速度减缓。
Two types of dry yeast, they are 1:1 interchangable in recipe but rise at different rate.
1. Active Dry Yeast - moderate rate of rising
2. Instant Yeast - faster rate of rising
两种最为普通的干酵母为活性干酵母和速溶干酵母。你可以等量换算这两种酵母，它们之间的差别只是在于发酵的过程的快慢。速溶干酵母比活性干酵母发酵更快。
Storage
Once the packaging is open, keep dry yeast in airtight container, store in refrigerator.
包装打开后，用剩的酵母可以保存在密封容器，存放在冰厨里。
Proofing of yeast
Spending 5-10 minutes to proof the yeast may save you the rest of ingredients in the event the yeast has died. This can happen if the yeast is not stored properly.
虽非必然，但事先醒发酵母可以确定酵母是活的，避免浪费烘培材料。
General guideline
8.4375g of dry yeast will raise up to 500g of flour
8.4375公克的干酵母可以醒发约500公克的面粉。
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