I was watching a video which stated that the #1 mistake people make with their Web site is expecting that a visitor will make a purchase on their first visit. They likened this to expecting to get married on a first date.
We know this doesn't happen: typical online conversion rates of 1-2% mean that only 1 or 2 out of every 100 visitors make a purchase (and it may not be their first visit).
Ideally, every one of your visitors would give you their e-mail address so that you could stay in touch. The reality is that even if you give someone an incentive (say, free shipping shipping included on their first order), only about 10% will do so.
Once you have their e-mail, you can send them periodic e-mail messages, building trust and interest over time by sending useful information. You can even automate the process of sending these follow-ups using an autoresponder (a program which automatically sends a sequence of timed, personalized e-mails in response to the initial receipt of an e-mail message from a site visitor). AWeber, Constant Contact, and iContact all offer autoresponders; your current e-mail marketing service may also.
(of course, you have to write the messages that an autoresponder will send, but once you've done it, you've automated a key part of your online sales process. And you can even hire someone to do the writing, although I recommend you stay closely involved to preserve your winery's "voice").
If you really want to use your winery Web site to sell more of your wine (or club memberships), building your e-mail list by offering a real incentive to sign up is a must.