Calculating Starter Flour/Water Contribution

[scpizza]

My formula spreadsheet dutifully factors in starter hydration to determine final dough hydration.  For example, if 100g of 100% hydration starter is added to my dough, my spreadsheet counts that as 50g flour and 50g water toward overall dough hydration.

But metabolic activities of starter culture by definition break down sugars in flour into CO2 and H2O.  Thus, a jar of starter after 12 hours of metabolic activity will have a higher hydration than it started with.

Has anyone grappled with this question and come up with a more accurate method for determining starter contribution to dough flour and water?  By visual comparison, I would estimate a 100% hydrated starter near its end has about the consistency of a 125% hydrated starter near its beginning.

[Bill/SFNM]

So let's say you know that at some point in the process the total amount of water has increased by x%. How would you use this information? All kinds of reactions involving water are occurring throughout the process (especially baking  ). Metabolic activity of the starter is a very important factor that can contribute greatly to the taste and texture of the final product. Do you believe that its contribution to the amount of water in the dough is a reason for this? If so, then would this be different from changing the hydration of the original dough or starter?
 

[scpizza]

I don't care about hydration changes beyond the initial mixing of the dough.  However, at the point of initial dough mixing, I'd like to have accurate and thus comparable dough hydration numbers between different batches of dough with different amounts of initial starter.  This, after all, is the whole point of bothering to factor in the hydration of the starter at all.