At a specific winery, standards call for an average wine fermenting time of $21$ days. Utilizing a new fermenting process, the owner of the winery suspects that the wine fermenting process will now take less time. Assume the owner collected a sample of $30$ batches of wine and found that the average fermenting time period was $20$ days for the sample. Assume a population standard deviation of $4$ days.

Test with $5\%$ significance if the average fermenting time is less than $21$ days.