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Test TA in grapes not wine?

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dbeck

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I just purchased a vinmetrica SC-300. We have a vineyard and need to test the acidity of our grapes before selling them. The only youtube videos I find demonstrate how to test the acidity of wine...not grapes.

We picked some grapes and crushed them in a baggie and then I took a 5ml pipette of juice and put it in a container and added 15ML of distilled water. I then started the TA testing by adding the TA Test drops to the juice. You were supposed to do that until the PH measured 8.2 Well...I got to about 5 or maybe a little more and all 5 ML of the TA test drops had been added.

That just doesn't seem right. If I did it correctly, then its telling me I need more than 5 ML of test drops and my acid level must be really high I'm guessing.

Any thoughts on if I did something wrong?
 

MisterEd

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I don't think the amount of distilled water is critical but are you supposed to add 10 or 15 ml of H2O to your juice sample? I use NaOH .1 solution in a 15 ml juice sample (no H2O) and divide by 2 to get grams per liter. That process requires around 15 ml of NaOH, give or take depending on the actual acidity. Those TA test drops must be pretty potent if they only supply 5 ml.
 

TXWineDuo

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Sounds like you followed the manual like I did, 5ml juice and 15ml distilled water. our Tempranillo Ta is off the charts too.
Either our NaOH is bad or we didn't let the particles fall out. I need to re-read the manual again I think that I remember when testing fresh must it either goes in fridge or microwave to settle out particles.
I hope someone who is a pro can tell us what is wrong.

TXWineDuo
 

bchilders

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The Vinetrica manual recommends "homogenizing your sample in a blender before proceeding; otherwise your TA values can be very inaccurate. Take 100 mL or more of your must and put it in a blender on high for 30 seconds. Allow solids to settle for 2 minutes before sampling or use a cheese cloth or mesh strainer to remove solids" SC-300 manual Vs 3.0a. It also calls for .133N NaOH TA Titrant, the formula will change based on the strength of the Titrant.
 

mfzona

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The NaOH titrant that that comes with the sc300 is 0.133N. This makes the calculation easy if you use 5ml of juice with 15ish ml of water. You just multiply mls of titrant used to get to pH of 8.2, by 2. Depending on what grape you are growing (whites) and where you are (cool climate), 10+ g/l TA is not out of the question. Here in the finger lakes, NY, we see that often, especially in the newer cold climate varietals.
 

MisterEd

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A paper coffee filter is a good way to strain the raw juice but you have to be careful not to squeeze it too hard or it will rupture.
 
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