8 replies to this topic

[kakeeler]

Hi all,

We got the Vinmetrica SC300 to try to keep better track of our numbers. It arrived this week, and we had sent some samples in for testing, so we thought this would be a good time to try it, since we'd have lab numbers to which we could compare them. The pH numbers were very close to the lab's. In fact, one number was dead-on.

The TA's were all significantly off of the lab numbers, though. For instance, the lab number of our Cab TA was .65. On the Vinmetrica, it came back as .56. We checked our measurements, recalibrated, used clean instruments, we're as exact as is possible, but those numbers keep coming back way off.

We watched the videos over and over; we've read the manual; we just can't figure out what is off.

Does anyone have any tips as to something they might have run into? Thanks for anything we could try. We're exasperated -- and yes, I'll call the company Monday, but it's Saturday night, and I really wanted this to work. Everyone else has had good luck.

Thanks!

K

[mokadir]

Is your NaOH solution standardized and/or fresh?

[kakeeler]

We got new solution with the machine, so it s/be fresh and standardized, although I will confirm that again on Monday -- doesn't hurt to ask!

[PEL]

Hi all,

We got the Vinmetrica SC300 to try to keep better track of our numbers. It arrived this week, and we had sent some samples in for testing, so we thought this would be a good time to try it, since we'd have lab numbers to which we could compare them. The pH numbers were very close to the lab's. In fact, one number was dead-on.

The TA's were all significantly off of the lab numbers, though. For instance, the lab number of our Cab TA was .65. On the Vinmetrica, it came back as .56. We checked our measurements, recalibrated, used clean instruments, we're as exact as is possible, but those numbers keep coming back way off.

We watched the videos over and over; we've read the manual; we just can't figure out what is off.

Does anyone have any tips as to something they might have run into? Thanks for anything we could try. We're exasperated -- and yes, I'll call the company Monday, but it's Saturday night, and I really wanted this to work. Everyone else has had good luck.

Thanks!

K

My guess is that if you sent three seperate samples of the wine to the same lab, the numbers would not agree exactly and in fact might be close to the range you gave. Don't know for sure but just guessing.

[kakeeler]

I'm going to do them again, now that I've cleared my mind. Maybe we tried to do too many things late in the day and we were just missing a big, major thing. The pH went fine. The TA just was way off. Hopefully, it will go better this time. Thanks!

[gregorio]

My guess is that if you sent three seperate samples of the wine to the same lab, the numbers would not agree exactly and in fact might be close to the range you gave. Don't know for sure but just guessing.

If that happens, you need to go to a new lab.

[kakeeler]

We focused on it fresh the next day and got to within.01 of the lab's numbers on the pH, the TA, and the SO2. We're going to get more precise ureters and better beakers and run mirror tests until we're feeling confident. Bottom line is that it works; we're the problem.

[Doyle]

The NaOH solution that the Vinmetrica uses is 0.133 N. This is a non standard solution in that you cannot go over to Vintners Vault or another local shop and purchase this concentration of NaOH. The value was chosen because it makes the TA calculation very easy when you use the 5 ml sample. Essentially it is 2 times the volume of 0.133N titrant.
One of the issues with NaOH is that it degrades in concentration with time once the bottle has been opened.
I mention this so that you don't try to keep this for a year and use it. You should probably purchase fresh titrant at the beginning of each harvest season.
The alternative is to purchase fresh NaOH of a standard concentration and do the slightly more involved math. ) 0.1N and 0.2N are pretty common. The math is described in the manual and you would just replace the 0.133 number with whatever your new concentration is.

[kakeeler]

Thank you so much for that info. It's really handy to have, so I don't go try to buy it at Vintner's Vault. I spent a lot of time on it today and have a much better understanding of the whole process. I'm going to continue to run mirror lab tests for a bit, and hopefully, I'll become more confident and be able to fly solo on my lab work.