Cheerios and the Omer
The Sefirat Haomer is connected to a significant law that even has applications today. On the second day of Pesach, an Omer sacrifice was made using barley as its main ingredient.
This sacrifice signaled that permission was now granted to use what was called ישן, or, old wheat. This referred to what may have been a winter crop that was harvested before Pesach. The Halacha is that such wheat cannot be used until after the Omer sacrifice is offered. And since there is no such sacrifice today, we wait until after the second day of Pesach.
A few years ago there was an issue raised regarding eating Cheerios in winter. The fear was that the oats were planted in the fall, and harvested in winter. This meant that the Cheerios could have been available for purchase before Pesach. There were those who insisted that this cereal should not be purchased until after Pesach when the Omer sacrifice would have been offered.
It must be that a certain devout Jew was given the information that General Mills did plant winter crops. In any case, these rules called ישן and חדש, definitely apply in Israel. There is some debate as to whether it is also a Torah law outside of Israel.
It is important to be aware that Sefirat Haomer has agricultural rules attached to it. And this explains the apparent contradiction in the Torah that says Matza should be eaten for six or seven days. If we used permissible flour, harvested at the proper time, that would give us seven day Matza. But if we had to wait to use our harvest, when we begin counting the Omer, we would be left with six day Matza. This is an aspect of the Omer, that is not so well known, that needed some clarification.