TA reduced after adding acid??

[bathman]

I'm a bit confused. I racked my Cab Sauvignon today having completed MLF a week or so ago. The pH was at 3.8 and TA at 6.6g/L. I wanted to reduce the pH slightly to 3.6 so added tartaric. On paper I should have added at 2g/L, but decided to only add 1g/L to avoid overshooting (based on reading others experiences). I also added meta-K at the same time. This was for 25 litres of wine, so added 20g of tartaric acid (decided to go slightly lower than 1g/L).

After adding the tartaric and meta-K in a small amount of wine to the bottom of the new tank, I then racked all the wine into the new tank. After giving it a further quick mix and letting it settle for an hour, I took another sample for testing.

The pH came out at 3.6 which is what I was after. However, the TA came out at 6.45g/L, lower than before the acid was added! Given I added about 1g/L of tartaric I was expecting TA to go up to around 7.6g/L. I did run the test again and got the same result.

So - has anyone seen this before or know why TA has apparently decreased? (or at least the measured TA).

A couple of things to note...

1. I always 'degas' the samples before testing for pH/TA by shaking rapidly in a test tube to release CO2. I don't heat the samples like some people do.
2. I decided to add the meta-K and tartaric acid together and mixed with a small amount of wine. Not sure if this was a good idea, as there was some kind of endothermic chemical reaction with the beaker getting really cold. Any chemists out there know what the reaction could have been? Hopefully the reaction did not produce something bad as I added it to the wine!
3. Post racking the tank is giving of some gas - given MLF has stopped and final SG was 0.991 then all I can think is that this is some CO2 degassing post-racking. Do others normally see this after racking?

All I can think of is that my earlier TA samples were skewed as they were not sufficiently degassed, and the sample I took after racking had degassed sufficiently that it counteracted any increase from acid addition.

Or could the Meta-K/acid reaction I noticed has somehow affected the TA??

Appreciate any thoughts/answers from more experienced winemakers here!

 

[Johnd]

Not sure what happened there, but you ended up with pretty good numbers. More importantly, how has the taste changed after the addition?

 

[bathman]

Not sure what happened there, but you ended up with pretty good numbers. More importantly, how has the taste changed after the addition?

Unfortunately I have a completely unrefined palette so its difficult to say...I can't tell much difference after the addition, it still tastes of wine and tastes ok. Don't notice it tasting like it has gotten too acidic. Fairly happy with how it tastes. But yes, like you say the numbers seem about right. Just have to decide whether or not cold stabilization is a good idea...

 

[stickman]

For the future, don't add the Kmeta to the solution of wine and acid. Adding the acid to a small amount of wine causes a low pH condition, and when the Kmeta is added to that acidic solution, the Kmeta decomposes to release SO2 gas. Any SO2 released before adding to the batch is lost, so you may not have added as much SO2 as you thought.

If you are at a pH of 3.6 that's good, though your TA may still drop further due to tartrates falling out over time.