“And you may not eat bread, parched corn or fresh ears until the middle of this day!” (Vayikra 23:14)
It is a negative commandment that we may not eat from the new grain before the end of the sixteenth day of Nissan, as it says “And you may not eat bread, parched corn or fresh ears until the middle of this day!”.
Amongst the roots of this commandment are that the main sustenance of the creations is through the grains, and it is therefore fitting to use these grains to bring an offering to Hashem who gave them to us, before the creations derive benefit from them. All of this is in order to enable us to reach the level when we can receive His goodness.
On the sixteenth day of Nissan we would have offered an offering from the new grain. It would be from barley as barley ripens before wheat. This offering permits us to eat all of the new grain.
Amongst the laws of this commandment are that which Chazal said that there are five species of grain which are included in this prohibition and they are wheat, barley, spelt, rye and oats. When the temple was standing, as soon as the sheaf offering had been brought up, the new grain was permitted in Jerusalem, and in more distant places at midday (as it would definitely have been offered before midday and we are therefore allowed to assume that it has been brought up). Nowadays, because of our sins, we have no temple the grain is biblically forbidden all day. In those places where they keep two days for the festival, the grain is rabbinically prohibited until the night after the seventeenth.
This prohibition applies in all places and at all times, whether the temple is standing or not.
It is likewise a negative commandment that one may not eat parched kernels from the new grain before the aforementioned times. This means to say that the prohibition applies even if we did not make bread from the grain, nor did we grind or sieve it, but parched wheat or barley in fire.
It is a negative commandment that we should not eat parched sheaves before the aforementioned times. Chazal said that if one ate bread, parched grain and parched sheaves one receives lashes for each one.