White wine from juice - 3 weeks and about to rack

[Raptor99]

Cold stabilization of a wine below ph 3.6 will push the ph even lower, how much is probably dependent on the buffering capability of the wine. It is counter intuitive that it goes that way. Also I've never seen much of a change in ph from the cold.

Could you please explain how this works? In the comment right above yours, @winemaker81 talks about chilling your wine to reduce acid. That makes sense if there is excess tartaric acid and it precipitates out. If there is not excess tartaric acid, then the pH probably won't change. But how could chilling increase the acid (lower the pH)?

 

[BarrelMonkey]

Could you please explain how this works? In the comment right above yours, @winemaker81 talks about chilling your wine to reduce acid. That makes sense if there is excess tartaric acid and it precipitates out. If there is not excess tartaric acid, then the pH probably won't change. But how could chilling increase the acid (lower the pH)?

It is, as @cmason1957 says, counterintuitive. Daniel Pambianchi has a good description in his Modern Home Winemaking book.

It's a manifestation of Le Chatelier's principle, which says that if the equilibrium in a chemical system is changed, the system will adjust so as to counter the change. Consider a simplified system where you have just tartaric acid and potassium tartrate in solution. Tartaric is a weak acid, so most of it exists in the protonated state (let's call it TH, where the hydrogen ion (H+) is bound to the tartrate ion, (T-)), and only a small amount is dissociated into free H+ and T-. If we precipitate out potassium tartrate, this reduces the tartrate ions (T-) in solution and so some of the TH species dissociates into H+ and T- to counter the effect. So we simultaneously decrease the total acid concentration (TH) but increase the hydrogen ion concentration (H+), ie lower the pH. (It's a bit more complicated in that there are 2 H+ that can bind per tartrate molecule, and this only holds for pH < 3.6, but hopefully the general argument makes sense?)

 

[cmason1957]

Could you please explain how this works? In the comment right above yours, @winemaker81 talks about chilling your wine to reduce acid. That makes sense if there is excess tartaric acid and it precipitates out. If there is not excess tartaric acid, then the pH probably won't change. But how could chilling increase the acid (lower the pH)?

I would love to explain it to you, but it is well beyond what I completely understand. There are many articles written about it on the web. Here is a link to one.

Wine Production | Penn State Extension

Curious to learn how to make wine? Access educational resources on wine production, wine acidity and tannins, grapevine diseases, and harvest season.

extension.psu.edu

 

[Raptor99]

@BarrelMonkey Thanks for posting the explanation. So the chilling the wine can potentially lower total acidity (TA) but at the same time lower pH.

@cmason1957 Thanks for sharing the link. From that article:

If the initial pH of the wine, prior to cold stabilization is below pH 3.6, then the pH will decrease as KHT precipitates out of solution, generating one free proton per molecule of KHT precipitated. If the initial pH is above pH 3.6, then the pH will increase as KHT precipitates out of solution (Iland 2004).

I wonder if that also takes place for citric and malic acid? Some of the fruits I use to make wine have very little tartaric acid.

 

[winemaker81]

I wonder if that also takes place for citric and malic acid? Some of the fruits I use to make wine have very little tartaric acid.

AFAIK, no. Just tartaric acid.