Now, another big concern...
I just saw this today on the Mercola site, so will be making my gaspacho (which is close to juice in a way) fresh every day:
I have previously written an extensive guide to juicing, which I highly recommend reading to help you get started. One important factor to keep in mind is that, since vegetable juice is very perishable, it's best to drink all of your juice right after you make it. However, if you're careful, you can store it for up to 24 hours with only moderate nutritional decline.
Additionally there is the concern that free methanol will be created once you process the juice and store it in a container. Methanol (wood alcohol) has been associated with autoimmune diseases like MS. Fresh fruits and vegetables contain small amounts of naturally-occurring methanol. Normally this is not a problem as the methanol is typically bound to pectin, and since your body has no enzyme to metabolize that bond, it is simply excreted in your stool and none of the methanol is absorbed into your body. However, the problem occurs when you can or bottle fruit or vegetable juice, as the methanol tends to then dissociate from the pectin into free methanol, which you do absorb.