Why can't winnowing be done in a closed room?

Winnowing requires the separation of chaff from grain using wind or air movement, which helps to carry away the lighter chaff. In a closed room, there is insufficient airflow to effectively remove the lighter particles, making the process inefficient. Additionally, the accumulation of dust and chaff in a confined space can create an unhygienic environment. Therefore, winnowing is best performed outdoors or in open areas to allow for optimal air circulation.