WHAT IS LEAVENING, AND WHAT IS NOT?
God uses leaven to symbolize sin, 1 Corinthians 5:1-8.   During the Days of Unleavened Bread, we picture putting sin out of our lives by putting leavening agents and all leavened products out of our homes by the First Day of Unleavened Bread.  To understand what is included in the leaven we are to avoid during the Days of Unleavened Bread, we must understand what is meant by "leaven".
Leavening agents are substances that are used to puff up or produce fermentation, causing dough to rise. Yeast, baking soda, potassium bicarbonate, and baking powder are such substances. Leavening can also refer to "sourdough" a naturally fermenting yeast batter. Foods that can contain the above leavening agents are bread, rolls, buns, cakes, some crackers, pancakes, waffles, doughnuts, certain cookies, cereals, etc.    
 FOLLOWING IS A LIST OF LEAVENING AGENTS
Baker's ammonia = ammonium carbonate = baking ammonia = hartshorn  
Baker's yeast  
Baking powder 
Baking soda 
Bicarbonate of soda or sodium bicarbonate
Single or Double-acting baking powder, which is the same as single or double-action baking powder  
Potassium bicarbonate
Sourdough starter (a yeast colony that is maintained with flour and moisture)
Yeast 

THE FOLLOWING ITEMS ARE NOT CONSIDERED TO BE LEAVENING AGENTS
EGG WHITES are not considered to be a leavening agent.   Egg whites do not spread thru dough as leavening does.  
YEAST EXTRACT on the labels of certain foods are derivatives of yeast that cannot leaven anything. 
BREWERS YEAST is a food supplement that contains all the elements of the B vitamin complex. It has no leavening properties.  
CREAM OF TARTAR is not a leavening agent, nor is TARTRATE POWDER, ALUM, TARTARIC ACID, 
         POTASSIUM BITARTRATE or POTASSIUM HYDROGEN TARTRATE.  
AUTOLYZED YEAST and CORNSTARCH are not leavening agents.  Autolyzed yeast is used as a flavor enhancer and cannot be used for making bread.
TORULA YEAST:  a dead yeast that cannot leaven bread, considered a nutritional yeast.  
SORBITAN MONOSTERATE:  A flavor and texture enhancer.  Not leaven of itself.
In preparing for and observing the Days of Unleavened Bread, always check the ingredients on the label to be sure. Just because a food looks unleavened (FLAT), it still may contain a leavening agent.