I copied this from something that I posted on another forum.
Understanding the Festival of Unleavened Bread and Leaven
 
This discussion is to discuss just what leaven was to the ancient Hebrews. When this is properly understood, then more significance will come from keeping the festival of unleavened bread. I will copy and paste some comments from another discussion, and then elaborate on them.

It will become obvious how this applies at the end.
Luci said to me (when she found out I was learning to make sourdough bread),

"I have a lovely starter my mother sent me from Montana that has been kept alive since coming from the gold rush days in California. It came through a Yellowstone ranger, then to a lovely artisan bread making family in Bozeman. It smells so appley and delicious, I am making some bread right now. It has a 7 hour rise time. Wow, will that be good. I am willing to share some if you want to pay shipping. "

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First of all we need to understand that the Hebrews did not just go down to the local market and buy some packets of yeast when they wanted to make bread. Commercial yeast as we know it, has only been available for less than 200 years. How did people rise their bread before this? They used what we refer to today as a sourdough starter.

Here is a brief run down on how to create a sourdough starter of your own:

1) obtain some grains of wheat.
2) grind the wheat
3) place the fresh flour, just a few tablespoons, in a container and add some water
4) wait about a day
5) add a bit more flour and water, wait another day

Here is a look at what will be happening…The grains of wheat have naturally occurring yeast on their surface, there may be many varieties of yeasts and other beasties on this wheat. When it is ground and water is added the yeast will start to feed on the starch present in the flour. Actually the first thing that starts to grow are usually bacteria.

After about a day, you will probably start to notice some bubbles forming in the runny dough mixture. This is in part from wild yeast, but at this point mostly bacteria. Each day you will add a bit of flour to continue feeding your future slaves (yes the yeast will be your slaves, they will be working for you, you must feed and nourish them so they will grow into a multitude).

The Land of Goshen

Just as Joseph gave his family the land of Goshen, the place where he knew they would prosper, the very best of the land, so we too must give the yeast the very best of living conditions. Just as the Egyptians thought that the Hebrew shepherds were detestable and did not want to live in the same area, so too is the dichotomy between the yeasts and the bacteria. We must create good conditions for the yeast, they will become greater in number, a multitude, and the bacteria will become less in number. This can be done in the start by using some fruit juice instead of water to add to the flour mixture. The yeast thrive in an acid environment and they will start to over power the bacteria.

One of the points of this discussion is to show that there is a big difference between leaven and yeast, at least this is what I am learning from my experience with making a sour dough starter.

As you continue to add a bit of flour and juice each day to the mix, the yeast will start to really come to life, the smell of the mixture will start to have a bread or wine smell, there will be that definite "yeast smell" that you get from beer, wine and bread dough. At this point you can just add water because the yeast themselves now, being strong in number, will make their environment acidic on their own. The bacteria will have now been overpowered by the yeast. The only bacteria left will be several varieties of lacto-bacillus, which are bacteria that thrive in an acid environment, actually producing lactic acid, which acts as a preservative, and protects from harmful bacteria. Doesn’t this sound like how the Hebrews almost took over the land of Goshen?

When will you be able to make bread?

Once your starter gets going, after about 3-4 days, you then will remove about half the mix each day and discard it. Lets say that you have 2 cups of starter…You will remove one cup, discard it, and then add enough flour and water to get it back up to 2 cups. At this point the yeast will gradually become stronger and stronger, but you still can not make bread yet, therefore you do not yet possess "leaven" (imo). What will start to happen soon is that your dough lump will start to grow. It should double in volume in about 12-24 hours, when it doubles in volume you will remove half and discard it, and again add enough flour and water to get it back to the original volume.

What you are doing here is feeding your yeast. Just like Joseph fed his family in Egypt. As the yeast multiply they are consuming the nutrients in the mix, so you need to constantly add more flour to feed your future slaves. The reason you remove half each time is because, if you didn’t, you would soon have an Olympic sized swimming pool full of sour dough starter, as it would be doubling in size each day!

So how long before the yeast colony is strong enough to make bread? About one week. Once a week has passed you MAY have what could be called leaven. You MAY actually be able to make some leavened bread.

The Process of Bread Making

I am no expert on bread making, but I am trying to learn. The book of Exodus mentions kneading troughs. These would be a concave trough or long shallow bowl made out of wood that they would have kept their sour dough starter in and also they would mix their dough in it.

Now imagine you are a Hebrew and you now have a viable starter in your kneading trough. You know it is ready to bake bread with because when you feed it, it will double back to its original size in about 7-12 hours. Now it is time to bake bread, you no longer have to throw out any of your mix. What you do is take your starter mix, and add to that enough ingredients to make your bread for the day, your daily bread. The starter you added to these ingredients will now have a field day and start to grow like crazy, and in the process they will be making lots of CO2 which will fluff up your dough. This may take a while longer than store bought yeast, but the job will get done. If they mixed their dough in the evening, it would be risen and ready to bake in the cool of the morning.

When the dough for the bread is made, you keep back some of the dough for the next day, and bake your bread with the rest. Now you have started a process where by each day you make bread, and keep some left over sourdough for the next day. Your starter, your LEAVEN, has become like a family pet, and a good starter can be almost as prized as a faithful family pet, maybe MORE prized than Rover.

So in my opinion, leaven is a functional lump of sourdough starter, it is not the same as wild yeast. Now what we might have in the cupboard, for us is leaven, because we can use it to make a loaf of leavened bread the same day, but it is nowhere near as prized as the leaven of the Hebrews. Their leaven had to be fed and nurtured in order to become strong! Their leaven took a minimum of a week to be made functional. When they threw out their prized starter lump, and it was prized, shared, traded, and loved, they would be very sad to do so. They may have spent a good part of the year developing the character that their starter (leaven) now had. This may be why the Festival of Unleavened Bread would last a week, because it would be impossible to make leavened bread again for at least a week. When the festival was over, they did not go down to the store to buy some packets of yeast, but their new lump would be almost ready now to be called leaven again.

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Just like keeping the Passover by actually killing a lamb, may give us more of an appreciation of what YHWH and Y’shua did for us, I think that we should all try to start a sour dough starter. It may help us to really appreciate the fact that the "leaven" of the Pharisees was something that had to be fed and nurtured.

What I think this is really pointing at is that we are to abandon our own "nurtured and fed beliefs" each year. We are to go back to the source, the Torah, read it and get some seeds/spores of truth. We are then to feed and nurture these ideas from the source into our beliefs. Just as each year the Israelites were to throw away their PRIZED leaven, that had developed some very nice characteristics, and start fresh, they were to go back to the source, the wild yeast, to nurture and feed a new lump, so we too have to be willing to abandon our "prized teachings" that have been shared and passed down for years. Perhaps we have developed ideas of our own that are prized in our eyes, each year we should abandon everything, and go back to the Torah, the source of our knowledge and wisdom, then we will get fresh insight, and our ideas will again be based on Torah.

Those who are experienced in making fine starters (leaven) may know a few tricks and things to add to improve the flavor; they will not take as long to once again have a fine lump of leaven.
 
Each year during the Festival of Unleavened bread, we need to go back to the Torah. Read only in the Torah all week long, abandoning our existing ideas and making sure all our beliefs are from the true source, Torah.

Next I’ll add a word study on leaven.

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Below is the Hebrew word that is translated as the English word leaven.

H7603
שׂאר
Å›e’ôr
seh-ore’
From H7604; barm or yeast cake (as swelling by fermentation): – leaven.

Below is the root it comes from.
H7604
שׁאר
shâ’ar
shaw-ar’
A primitive root; properly to swell up, that is, be (causatively make) redundant: – leave, (be) left, let, remain, remnant, reserve, the rest.

Do you see how the Hebrew letters are the same for both. The only difference are the vowel pointings, which were not present in the original text. Therefore one had to discern which word to use by the context. The roots though, will always have a related meaning.

So how is "swelling by fermentation" related to "left over, or remaining"? In our western understanding of leaven this makes no sense what so ever, but in the Hebrew understanding of leaven, the relationship is very obvious. The word leaven comes from the root left over because you always make sure to have some of your leaven left over for your next batch of bread!

Now if we do a word search for H7604, the root of leaven, "a left over" lets see what comes up.

Gen 7:23 So He wiped off all that stand, which were on the face of the ground – both man and beast, creeping creature and bird of the heavens. And they were wiped off from the earth. And only Noaḥ was left [Noah was the leaven left to start a new beginning (loaf)], and those with him in the ark.

Gen 32:8 and he said, “If Äšsaw comes to the one group and attacks it, then the other group which is left shall escape.” (If part of Jacob’s family was destroyed, there would be some left over, some leaven, to begin again)

Gen 42:38 But he said, “My son is not going down with you, for his brother is dead, and he is left alone. If any harm should come to him along the way in which you go, then you would bring down my grey hair with sorrow to the grave.” (the sons of Rachel have been divided, and in Jacobs mind one half had been destroyed, he did not want to part with what was left over)

It is obvious to see the connection here. leaven is always left over in part when you bake bread, so that you can continue to bake daily. Leaven does not represent sin, but it represents something that has been fed, nourished and cherished. Leaven represents our ideas and teachings that we feed, nourish, cherish, and share with others. The great sin of the Pharisees was that they refused to let go of their own teachings each year, and go back to Torah. Their teachings gradually grew into something of their very own with very different characteristics than what they originally got from the scriptures. They had in effect broken the Festival of Unleavened Bread in a spiritual sense for many many years. That is why Y’shua warned to avoid the leaven of the Pharisees. It was not that leaven was bad or sinful, but that the Pharisee’s leaven, or prized teachings had strayed way too far from the Torah.

Y’shua’s leaven or teachings were straight from the Torah. He constantly returned to the source, the Torah, the "wild yeast", to form his teachings, HIS leaven.

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Now let me alter Luci’s comments she sent me…

I have a lovely starter [teaching] my mother sent me from Montana that has been kept alive since coming from the gold rush days in California. It came through a Yellowstone ranger, then to a lovely artisan bread making family in Bozeman [there is a long tradition conected to this "teaching"]. It smells so appley and delicious[this teaching is appealing to almost everyone], I am making some bread right now [I'm applying this teaching in my life right now]. It has a 7 hour rise time [This teaching was put on to a 7 hour DVD set, I'm sure this teaching will have good effects in my life].Wow, will that be good. I am willing to share some if you want to pay shipping [I'll send you a copy of this DVD set if you pay the shipping].
 
Shalom,
 
Greg

A light look at a modern day Passover.