26On the day of the first fruits, when you offer up a new meal offering to the Lord, on your festival of Weeks; it shall be a holy convocation for you, and you shall not perform any mundane work.
On the day of the first fruits: The festival of Weeks [Shavuoth] is called the first fruits of the wheat harvest, because of the two loaves, which were the first of the wheat offerings to be brought from the new [crop]. — [Men. 84b]
they shall be unblemished for you, as well as their libations: Even the libations shall be unblemished. Our Rabbis learned from here that wine that has turned moldy is unfit for libations. - [Men. 87a]