The question asks why it is that wines or musts with
different TA’s can have the same pH and vice versa.
a must or wine there are both free and bound, hydrogen
pH is a measurement of how many free
positively charged hydrogens are around.
When measuring TA, you add sodium hydroxide to the
must. What happens is, you deal with the free hydrogens, those
responsible for the pH. But even as you do and as you continue to add
more sodium hydroxide, you actually start to unhook bound
hydrogens and make them free.
Only when you have added sufficient sodium hydroxide
to unhook all accessible hydrogens is your measurement of TA complete.
Since the proportions of free and bound
hydrogens varies greatly according to grape varietal, ripeness, growing
conditions and so on, so does the relationship between pH and TA.
© Charles Plant 2001