We read in Matt 16: 6-12 (NRSVCE):
Jesus said to them, “Watch out, and beware of the yeast of the Pharisees and Sadducees.” They said to one another, “It is because we have brought no bread.” And becoming aware of it, Jesus said, “You of little faith, why are you talking about having no bread? ........... Then they understood that he had not told them to beware of the yeast of bread, but of the teaching of the Pharisees and Sadducees.
In the days of Jesus when dry yeast was not in vogue, people preserved a small portion of leavened dough, for use on a subsequent occasion. This is clear from the Parable of the Yeast in Mtt 13:33:
He told them another parable: “The kingdom of heaven is like yeast that a woman took and mixed in with three measures of flour until all of it was leavened.”
If the woman needed one measure of yeast for three measures of flour, it would not have been in the form of dry yeast we have these days, but of leavened dough set apart from previous baking.
Now, leavening was considered good because it gave taste and softness to the bread and increased its shelf life. There were two options available to the breadmaker: he/she could refresh the leaven day after day by preserving the leavened dough of the most recent baking. Alternatively, one could preserve a large portion of leavened dough from the first day of baking say, Sunday and use small portions of it for leavening the flour through the full week. That would make the leaven too sour for want of renovation, but it would still act as a leavening agent.
The Pharisees and Sadducees clearly showed scrupulous adherence to the Old Law which Jesus wanted to supplement with the New Law. Jesus' way of referring to the yeast, was meant to expose the confrontation. In the literal sense, he was referring to the fermented dough that had been kept too long, but it was still being used as a leavening agent. My question therefore is: Did Jesus have in mind the tradition of preserving of leavening agent, while speaking of the Pharisees' Yeast? Inputs from any denomination are welcome.