Bigfoot is brewed starting in late November and is released in the middle of January. Not all the beer is brewed at the same time or shipped out at the same time. We usually brew off and on for about two months and then those batches are blended over several packagings. It does take some time to ship, arrive at the distributor and then get out to the retail outlets. Tank times are usually about a month, with fermentation taking about 10 days, followed by cold storage in the fermenters. You will find the bottling date on the side of the bottle. After bottling, it takes another 14 days to bottle condition the beer in our warehouse. Then it is shipped to the distributors. I included a link on the instructions of reading the bottle date code.
http://www.sierranevada.com//codehelp.html