pH mismatch

[mendozer]

Got my grapes today and took them home for testing. I got 3.71 and 3.72 for my pH for the two different batches. Vineyard measures were 3.44, 3.38 according to the grower. I calibrated my pH meter as always. Even though I did a So2 test (accuvin) I got what looked like 18ppm for one and 28 ppm for another. I just calculated sulfite for 50 to be safe for both so 3.44 gr/3.68 gr based on the volume. I used to calculate the difference in years past (so 50 minus the 18ppm for example) but this year I wanted to just shoot for one level early on since I had a little flowers of wine last year.

any input from the pros?

 

[Johnd]

How, exactly, did you take your sample for testing? You should be removing a 1/2 cup or so of must, running it in the blender for a short time, straining away all of the solids to get a nice clear juice sample.

Secondly, even if you don’t do that, the readings can vary due to location in the vineyard that they sampled vs where your grapes came from. The values change as the fruit hangs too, so if yours was picked a few days or more later, that can be the variable.

Last, if you’re planning on MLF, and the fruit is good, my inclination would be not to add any sulfite.

 

[Rice_Guy]

The pH meter does black magic, ie you don’t really feel/ have sensory input of what is real.

* from a practical point I would ignore any error less than +/- 0.05 unit, home meters will vary, only expensive research meters are accurate to three places. A difference of 0.3 units is enough that I would look for an answer.
* the food industry puts a lot of effort into accurate pH since it is a control point on what is safe/ legal. As a cross check on your instrument you could cross check against formulated foods ex. fresh canned SevenUp ,3.48 , or Pepsi , 2.49 , or Kroger MDew ,2.98 , or even tooth paste , Crest 7.21 , and the juice out of Milwaukee dill pickles ,3.92 . Another cross check is check your readings against others on similar juice, , the local club compares results on buys of buckets and I see my meter’s number vs. others who got buckets.
* temperature is a highly likely “expected” variable, does your meter/ the vineyard meter have automatic temperature compensation? Was the calibration solution at some other temperature. The older/ less expensive meters are good as long as you are at room temperature, 20C.
* buffers tend to last if sealed against CO2, if open to air they will degrade. There are single use travel size pouches of buffer that eliminate this source of error.
* a dirty probe will give a slow reading, eventually gets to the same number but takes linger, with John’s test method large solids are removed, large solids can also give a slow reading. It isn’t necessarily a wrong reading with solids for example you are fermenting whole berries instead of juice. (A probe measures the electrical potential of KCl leaking into the sample ie a small hole)
* you were not dealing with frozen, ice would concentrate the soluble solids
* finally the probe is rinsed with distilled water after each use and stored in KCl storage solution or pH 4.0 buffer. You/ the vineyard could have mold growth if it gets dirty.

At this point I would recalibrate my meter and take the fresh reading as the real number accurate to 0.1 unit

 

[mendozer]

I did not strain it, i'll do it again today.
my pH is an anaheim scientific, not el cheapo but not pro grade and i believe it has ATC. I take it out of the storage solution, rinse it with water and dry, then calibrate in ph 7, adjust if needed, then ph 4, then rinse and dry again and off we go. I do this every time since it sits for so long between uses.

 

[Rice_Guy]

You calibrate against a known, so you should be doing good readings, , ,
that said you have no idea how careful the vineyard is, they may only use the meter two weeks out of the year.

I did not strain it, i'll do it again today.
my pH is an anaheim scientific, not el cheapo but not pro grade and i believe it has ATC. I take it out of the storage solution, rinse it with water and dry, then calibrate in ph 7, adjust if needed, then ph 4, then rinse and dry again and off we go. I do this every time since it sits for so long between uses.

 

[Johnd]

I did not strain it, i'll do it again today.
my pH is an anaheim scientific, not el cheapo but not pro grade and i believe it has ATC. I take it out of the storage solution, rinse it with water and dry, then calibrate in ph 7, adjust if needed, then ph 4, then rinse and dry again and off we go. I do this every time since it sits for so long between uses.

If you’re confident in your readings, then base your actions upon your readings. Just as @Rice_Guy said above, you don’t know how diligent the vineyard / vineyard employee is either.

 

[mendozer]

I tested it again after picking up new calibration solution just in case. now I got pH of 3.87! But also.... I sulfited it last night to 50 ppm so that might have played into it. my TA was 9.4 g/l and 5.8 g/l. last night those batches tested at 8.3 and 6.4 in that order. Tonight was blended and strained must vs just trying to get nice juice last night with syringes

 

[Tim3]

Sounds like your adjustments depend on how confident you are in your readings. I’ve routinely found growers will misrepresent their acidity, depending on the quality of the grapes. For what it’s worth I depend on my own readings and not what I read / hear from nondescript growers. Now if I’m buying from Brehm I’ve found those posted numbers are accurate. Where did you get your grapes?

 

[mendozer]

Eclectic vineyards in Prosser,was. They sell mainly to home winemakers and boutique wineries. My question is since the TA was high, I can't really add more tartaric to lower it without making it too harsh. Perhaps I can just make sure to limit oxygen while racking and adding the MLF culture then measure so2 before aging