se’or (7603) is the “leaven”. Fausset’s Bible Dictionary refers to this as “A lump of old dough in high fermentation” (basically a lump of sour dough). Strong’s Lexicon refers to this as “barm or yeast-cake (as swelling by fermentation)”. Gesenius’s Lexicon also makes mention of “fermentation”.
chametz (2557) is the bread you make with the leaven. Strong’s Lexicon indicates that this comes from chamets (2556) meaning “to be pungent; i.e., in taste (sour, i.e. literally fermented…)”
Matstsahx(4682) is bread or cake without leaven. Gesenius’s Lexicon refers to this as “unfermented bread”. Strong’s Lexicon also specifies “not soured or bittered with yeast” and “an unfermented cake or loaf”.
In the fermentation process, yeast consumes sugar and expels gas. It’s the gas which causes the bread to puff up. Similarly, baking soda (when combined with an acid) produces a chemical reaction which expels carbon dioxide gas bubbles that cause the dough (or batter) to puff up. While there is no chemical reaction involved, beaten egg whites can also be used in a similar wa...it’s the air that’s incorporated in when the egg whites are beaten that causes batter to puff up.
There is a major difference between the use of baking soda/baking powder/beaten egg whites as leavening agents and the use of yeast. As we see from the definitions above, the leavening spoken of in the Bible involved fermentation. Also, the leaven referred to in scripture is something that spreads throughout the dough. As we see in 1 Corinthians 5:6 and Galatians 5:9, a “little leaven leavens the whole lump”. Yeast is a living organism. If you hide a little bit of yeast (or sourdough) into one part of a lump of dough and let it sit, eventually the yeast will ferment and spread throughout/leaven the whole lump. This is not the case with baking soda, baking powder, or beaten egg whites. If you put any of these into your dough/batter, you have to manually mix it in to get it throughout. There is no fermentation involved, so it will not spread throughout on its own. The lack of fermentation is why many Jews consider baking soda or baking powder to be acceptable for Passover/Unleavened Bread. While I’d argue that if you’re using something for the specific purpose of puffing up bread, then you’re using it as a leavening agent and breaking the spiritual principle of Unleavened Bread, it is true that baking soda and baking powder do not meet the Biblical definition of “leaven”.
It’s also interesting to note that the Hebrew terms above refer to bread or dough. Fermentation alone does not make something “leaven” according to the Biblical definition, but it has to be mixed into a bread product. This would, therefore, exclude beer, yogurt, and other fermented items (when NOT mixed into a bread product) from being the type of “leaven” we are commanded to remove from our homes.
Just as egg whites can be used to “leaven” bread products while not technically being “leaven”, baking soda and baking powder can also be used to “leaven” bread products while not technically being leaven according to the Biblical definition. How many of us who avoid things puffed with egg whites actually throw away all our eggs before the Feast of Unleavened Bread? Throwing away our eggs would seem silly because we all know that they are not, of and by themselves, leaven (though they can be used as a leavening agent). The same is true with baking soda & baking powder…while they can be used to puff bread products, they are not “leaven” according to the Biblical definition of “leaven”. As we saw in Exodus 13, God tells us that we are not to be seen with any leavened bread or have any leaven (barm or yeast-cake) in our quarters. The only reason we would have yeast or sourdough in our homes would be to leaven bread products. Baking soda, on the other hand, isn’t just for “baking”, but has many other personal care & household uses that don’t have anything to do with “leavening”. While I see bread products puffed by any means (Biblical definition of “leaven” or not) as breaking the spiritual principle of Unleavened Bread, I see nothing in scripture indicating that God wants me to toss out something that’s never going to be used as a leavening agent.
Beyond household uses, why do they put baking soda in some canned beans? Is it some sort of evil attempt to sneak leaven into our homes during the Feast of Unleavened Bread? The baking soda in canned beans is not being used as a leavening agent. It’s added as a firming agent to help keep the beans stable and not mushy. This is much different from the lump of fermented dough sitting in a bowl in your house just waiting to leaven some bread. As far as I can tell, there is no scriptural indication that God has an issue with people keeping their beans firm during the Feast of Unleavened Bread. However, I still wouldn’t bring them to a church potluck for the sake of those whose consciences would be bothered by such things.
Another interesting fact about baking soda: Baking soda is a chemical compound with the formula NaHCO3. This formula is shared by the naturally occurring mineral known as nahcolite. Nahcolite can be found in rivers, lakes, and springs and can be found both in Egypt and Israel (among other locations). This naturally occurring sodium bicarbonate could have been found in some of the water the Israelites were drinking as they observed their first Passover & Feast of Unleavened Bread. Yet God never mentioned anything about being careful to only drink unleavened water. It is the Feast of Unleavened “Bread”. If God wasn’t so concerned about a bit of sodium bicarbonate in the water, then why should we fret about a bit of sodium bicarbonate in our mineral water, toothpaste, dishwasher detergent, etc?