I've never been clear on what volumes to test/adjust with respect to both pH and TA in red must. Having just picked up a 1000lbs of Merlot, I'm really anxious to get the acid adjustment right before my primary fermentation ends.
At crush, I took a sample of must, both free-run and grapes, attempted to press and strain the combined juice, then titrated TA and measured pH. My results showed:
TA of 4.25 g/L pH of 3.82
23.25 BrixI decided to initially raise the acid by 1 gram of tartaric. My first question is how should that 1 gram per litre be calculated, on the volume of the must (420L) or the volume of expected juice after pressing (approx. 310L - according to literature I've read). I chose the latter and added 310g of tartaric to my must.
I tested the following day using my 'press and strain' technique and got the following:
TA 5.75 pH 3.63
23.50 BrixThe sample also tasted pretty bland.
I also drew a sample of free-run and tested the pH, which was 3.39. This sample tasted very tart.
Now, I'm torn on whether or not to add more acid (I started the ferment last night). I understand starting a ferment above pH 3.5 is a bad idea, but which number (pressed vs. free-run) has more meaning? Pressing seems really inaccurate, simply because one can't ensure a consistent ratio of free-run to berries and the berries don't press very well. I'm also concerned that dropping the pH of the free-run any lower will cause problems for my ML, which I plan to inoculate towards the end of ferment.
Any help would be most graciously appreciated.
Darin