I think what you're after is to heat the most
juice with the least wasted energy (increased coil surface area in contact with the
juice) without burning the juice. That is worthwhile if your power source is the limiting factor. With today's power sources, I don't think power is the limiting factor. If you want more coil surface area in contact with the juice, use thicker wire. It will require more power, but try that first to see if more juice contact is really what you're after.