Strange ph question

[orto]

I had a sample in shot glass. I checked its ph, it was 3.57. I put the glass in a ziplock sandwich bag and planned to check the TA the next day. Before I did the TA test I checked the ph again and it was now 3.4. If anything it should have gone up as carbonic acid left the solution. Why did the ph drop? Is this sample still representative of the batch after sitting. Does this mean the TA is inaccurate.

Thanks

 

[BernardSmith]

Two quick thoughts - 1. How often and at what levels do you calibrate your pH meter? and 2. How stable is the plastic of a ziplock when exposed to alcohol, CO2 and acidic outgassing?

 

[orto]

Two quick thoughts - 1. How often and at what levels do you calibrate your pH meter? and 2. How stable is the plastic of a ziplock when exposed to alcohol, CO2 and acidic outgassing?

I calibrated the meter before the first test but did not recalibrate before the second since only one day had passed. I'm sure some outgassing took place through the bag my guess would be mostly CO2, but if anything CO2 leaving should raise the ph. The wine did not smell as good the second day it smelled stale. I guess I'll take another sample in a week or so. thanks

 

[mikewatkins727]

Does your pH meter have ATC (automatic temperature correction)?

 

[orto]

Does your pH meter have ATC (automatic temperature correction)?

It has a temp probe, I let it sit in the shot for 30 seconds or so before putting in the ph probe. I rinsed the storage solution off with distilled water before putting the ph probe in.

 

[Johny99]

Calibrate it and check again. A day can make a difference.

 

[orto]

Yeah, I guess so. I was just wondering if removing the sample for a day changed it.

 

[GreginND]

Was this filtered juice or with some grape flesh or skin? Some buffering of the acid could occur as various components are released from the pulp.

 

[orto]

Was this filtered juice or with some grape flesh or skin? Some buffering of the acid could occur as various components are released from the pulp.

Whole grapes, pressed last Friday. I was wondering if the ph changed from being oxidized because it sat for a day and had a sort of stale smell the next day.