"Tim O'Connor" > wrote:
> To me this is an important issue because I am constantly topping up barrels
> so I need to keep the sulfites up (for the periods between top ups). So
> what do others do? New sulfite every six months and keep good notes or rely
> on titret measurements?

Keeping good notes and frequent sulphiting isn't enough because you
need to accurately account for SO2 binding. You really need a
measurement of the free SO2 to be able to do this (since every wine is
different in its binding potential). Titrets are tricky, but with some
value adjustments and/or reference measurements you can get consistent
results of an accuracy that is sufficient for general practise. For
more, see sections 14.3-14.5 at:

http://members.tripod.com/~BRotter/SO2.htm

Ben