Tartaric Crystals? pH change?

[Fencepost]

I made 2- 6 gallon batches of Muscadine, one Red one White. Fermentation went well but in the 6 gallon carboys, after 3 months of clearing, I noticed lots of crystals in the bottom of the white wine carboy... lots, probably covered 50% or more of the bottom of the carboy. I wanted to rack it off the crystals and I did so for both white and red. The red wine carboy had lots of crystals left behind once it was racked as well. I assumed these are tartaric crystals that I have read about on this forum.

Originally, the pH for the red was 3.24 and for the white was 3.14 (adjusted using kbicarb as learned on this forum and help from @Rembee ) but I took samples after racking, thinking that the pH would go up, due to tartaric acid crystals dropping out but, lo and behold, the pH went down on both. Red was down from originally 3.24 to 3.00 and White from 3.14 to 3.10.

Now the question... if that was actually tartaric acid crystals dropping out, why did pH go down? I would have thought with less acid, the pH would go up, and I thought in general pH goes up in wines over time (that may be my misunderstanding from some threads I had read).

Used the Apera 60 pH meter (as recommended by some on this forum). It was calibrated and checked. I can provide ferment details if needed.

Thanks for any input to clarify this situation.

 

[cmason1957]

Here is a scholarly article on cold stabilization. That's essentially what has happened, your wine got cooler and potassium bitartrate dropped out.
https://extension.psu.edu/cold-stabilization-options-for-wineries
Why did your ph go down? Below ph of about 3.6 that's what happens, I think it's more potassium at lower ph than tartrate. How does it taste now becomes the question? Based on taste, not just numbers, you may want to adjust the ph, but probably not. Backsweetening does wonders for extra tart wines.

 

[stickman]

The change in pH you describe is normal and related to the wine chemistry, which isn't intuitive. The short answer is that during potassium bitartrate precipitation (crystal drop out), if the ph starts below 3.6 then the resulting pH will drop also, if the initial pH is above 3.6 then the resulting pH will rise. The important thing to know is that in both cases, the crystals dropping out represent an acid reduction, so the TA will be reduced and tartness will also be reduced.

 

[winemaker81]

My thanks to @cmason1957 and @stickman for today's chemistry lesson! The pH dividing line is an important thing to know.

I often say I learn something new about winemaking every week, and this topic illustrates that.

 

[Fencepost]

Thanks, Guys! @cmason1957 @stickman You mention that TA will be reduced and tartness would also be reduced below 3.6, funny that you mention this as I described the Red Muscadine wine to @Rembee as "a bit flabby" (not a technical term but as good a description as I could come up with), I could not fathom how dropping out acid could reduce tartness until I read your comment. Makes perfect sense based on what I saw and what I tasted. Any ideas to "unflab" the red muscadine? White was not as bad.
You guys are the best!

 

[cmason1957]

You can add acid back in. You might want to do bench trials as to the type of acid. Citric, tartaric, acid blend, ascorbic. Not sure which one is best for this.

 

[winemaker81]

Go light on ascorbic acid, as it produces a more acidic reaction than the other acids. When upping acid, I'd go with blend or tartaric.

 

[Rembee]

This is very informative in deed. As @winemaker81 said,

thanks to @cmason1957 and @stickman for today's chemistry lesson!

This is why I love this forum, the knowledge base here is unbeatable!

@Fencepost, I normally add tartaric acid to my Muscadine wines if this is of any help. Although it might be best to stick with the original acid that you used when adjusting the must. I don't recall which one you started with. Just remember to add small amounts at a time and let the wine rest in-between each addition of acid. No matter what acid that you decide to go with. That way your not chasing the pH all over the place.