Thank you for the clarification. Comparing the sin nature to a yeast is a great analogy and it certainly is rooted in Jewish thought. When it comes to differentiating midrashim from false teachings, you really have to seek guidance from The Spirit. History is full of rabbis disagreeing and even though tradition tends to side with one side of the argument, many times the other side of the argument has valid points.
A great example is the argument over what order to place and then light the candles for Hanukkah. In practice, it doesn't really matter how you do it. But it was a serious argument because the rabbis were attempting to establish new laws by which every Jew could live after the vast majority of God's commandments could no longer be practiced because of the destruction of the temple. Rabbi Hillel taught that the number of candles being lit should be the same as the day of the festival, while Rabbi Shamai taught that the Hanukkiah should start full and we should light one less candle each night.
Shamai's reasoning was that the first Hanukkah was a stand in for Sukkot because the Greeks held control of the temple during the Maccabean revolt and the sacrifices to be made during Sukkot weren't possible. Since the sacrifices during Sukkot decreased by one each day, so should the candles we light in lieu of the sacrifices. Hillel argued that, just as the blessings of God increased with each victory in the revolt, so should our celebration increase each night with the final night being the most joyous and therefore well lit.
Both arguments hold merit and are perfectly reasonable. However, if you observed Hanukkah according to Shamai, most Jews would decry it as wrong practice at best.
The only way to know if something is truly wrong practice is through prayerful communion with God through the presence of The Spirit in your heart. You can always confirm things with another Spirit-led brother or sister in Christ, just be sure the person with whom you are seeking council is actually living by The Spirit.