Acid adjustment questions

[Paulie vino]

This year Im making a grenache syrah blend, 2 lugs of grenache and one box of syrah. Brix was 23. I then measured the pH however I used opened 1 year old solutions to calibrate my meter so I'm not entirely sure how accurate these measurements are. I did a 2 point calibration so hopefully this improved the accuracy. The initial pH was 3.89 and the ta was around 0.5. The following morning I made an acid addition, mixed the must and let it sit for a hour or two then remeasured. The pH dropped to 3.43 and the ta was between 0.7 and 0.8 which should be a better place. I used about half of the calculated adjustment and I'm glad I did. This was my first time making an acid adjustment so I was cautions to avoid adding too much.

Some questions though:

1) I added yeast prior to the acid addition, so when I remeasured the brix it has dropped by about 0.5, would the start of fermentation impact the pH reading? Fermentation was just barely starting at the time I remeasured.
2) how does everyone else measure ta? I use a pH meter and add NaOH until the meter reaches 8.2. then use fermcalc to do the calculations.
3) when would be the next best time to measure pH or acid again? Can I do it during fermentation or shortly after it's done? I think I read somewhere that the dissolved CO2 may mess with the readings.

 

[ChuckD]

Those solutions are pretty stable. Maybe not good enough for a certified lab but they should get you within a tenth. I generally take pH readings whenever I pull a sample for measuring SG.

I do TA with the pH meter. I think it’s more accurate than the color change detection. Especially with reds.

 

[Rice_Guy]

The buffer solution will be good enough for home wine.
I use the pH meter for TA. I weigh samples since if I am doing a batch of 36 samples I don’t have enough 10ml pipettes. The acidity can be expressed as a percentage by weight as well as by volume. The conversion is your specific gravity reading. Most of my notes are based on weight in a pail or carboy etc so it makes sense.
CO2 can change pH readings. I freely sample sparkling wine and ciders. Normal is that the pH shifts up by 0.05 to 0.10. NOT down. I will degas all sparkling samples for a gravity reading and rerun. TA is not significantly affected.

 

[BarrelMonkey]

I then measured the pH however I used opened 1 year old solutions to calibrate my meter so I'm not entirely sure how accurate these measurements are. I did a 2 point calibration so hopefully this improved the accuracy.

I previously posted my results from testing year-old pH standards here. YMMV of course but as long as you're taking aliquots to use for standardization (as opposed to just dipping the pH meter in the bottle of standard solution) I think you'll be fine.

I used about half of the calculated adjustment and I'm glad I did. This was my first time making an acid adjustment so I was cautions to avoid adding too much.

Good call - wine is a complex mixture and it's well worth a bit of extra work to get it right.

Some questions though:

1) I added yeast prior to the acid addition, so when I remeasured the brix it has dropped by about 0.5, would the start of fermentation impact the pH reading? Fermentation was just barely starting at the time I remeasured.

Probably fine if it's barely started. But if it's well underway, the dissolved CO2 will have a significant impact on pH (ie make it seem more acidic than it is). If you want to accurately measure fizzy samples you need to centrifuge/filter out the yeast and thoroughly degas. (I degas my samples by shaking vigorously in a sample tube and 'burping' the lid until no more gas comes out.)

2) how does everyone else measure ta? I use a pH meter and add NaOH until the meter reaches 8.2. then use fermcalc to do the calculations.

I prefer pH meter to phenolphthalein, it's much less subjective especially for red wines. I normally adjust the distilled water in my beaker first to pH ~8.2 - since it's unbuffered it will change rapidly with NaOH addition so I typically only need a few drops of 0.01N (a lot less concentrated than what you use for titration!) It doesn't have to be accurate as any changes during titration over pH 7 or so go really fast.

For 0.1N NaOH and 5mL sample, TA (g/L) = mL x 1.5. For a 10mL sample, TA (g/L) = mL x 0.75

3) when would be the next best time to measure pH or acid again? Can I do it during fermentation or shortly after it's done? I think I read somewhere that the dissolved CO2 may mess with the readings.

If you want to you can measure again when primary fermentation is done; natural degassing will take a while so be sure to degas the sample in a tube as described above. I don't normally bother until I've completed ML (if that's what I'm doing) and/or added SO2 and gven some time for the wine to settle/degas. I always pH/TA measure prior to bottling.

 

[meridaen]

Really handy Q’s and A’s thanks lads