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PH, TA & Cold Stabilization

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DG2001

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I have a white wine that I added too much tartaric acid to. pH dropped to 3.06 and TA went up to 8.5, which is a little to acidic for my taste. I know if I cold stabilize it will lower TA but I'm a little confused about what will happen to the pH. What I have read on Winemaker Magazine states that depending on the pH, it could go up or down. Can anyone help me with understanding this? I want to make sure that I don't lower the pH even more.
 

skeenatron

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Cold stabilizing will drop some tartaric acid out of solution so you can rack off of the crystals. It will lower your TA and possibly increase your pH, but not by a whole lot. Then again you have a good amount of tartaric in that wine so it may be more drastic than normal. Doesn't hurt to do it though and will certainly not make your wine more acidic.
 

Boatboy24

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With pH/TA in those ranges, cold stabilization, along with Calcium Carbonate will help. It is when you are at/near 3.6 that it gets tricky and can actually raise your TA/lower pH.
 
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Johnd

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If you CS that wine, the pH will decrease, see the attached clip below from PSU. When the pH is below 3.6, CS DECREASES the pH (increase acidity). If your pH was above 3.6, CS would increase the pH (decrease acidity). If you want to increase the pH, look to one of the products that will increase your pH WITHOUT the need for CS to precipitate out the acid.

Sorry for all of the chemistry talk below. The referenced chart didn't come through in the cut/paste, but the information about the pH reaction to CS in the last paragraph is the important part........

"Theory of Cold Stabilization

Cold stability is a method of separating unstable natural ionic salts (potassium: K+, calcium: Ca2+, bitartrate: HT-) from wine. After fermentation, but prior to bottling, cold stability is conducted to prevent the tartaric salt, bitartrate (HT-), from precipitating out of the wine when stored and/or chilled post-bottling.

Precipitation occurs due to the instability of tartaric acid in its bitartrate salt form, which is known as potassium hydrogen tartrate (KHT) as a supersaturated solution. KHT is commonly referred to as potassium bitartrate or cream of tartar, and accounts for much of wine’s sourness or tartness (Butzke 2010). Instability occurs when the concentrations of potassium (K+) and bitartrate (HT-) bind to form the KHT product that exceeds solubility in the wine (Iland et al. 2004), thus precipitating out of the wine.

The pH of wine should be checked prior to cold stabilization as pH affects the efficacy of stabilization techniques. A higher pH wine (>3.6) will precipitate out more KHT in comparison to a lower pH wine (<3.6) (Church 2004). This is due to the percentage of the HT- present in the wine at a particular pH. The amount of tartaric acid in HT- form, as a function of pH, is illustrated by the acid stability curve seen in Figure 1.

boultontartaric acid chart

Figure 1 was provided courtesy of Dr. Roger Boulton in 2012, University of California, Davis.

As seen in Figure 1, the maximum concentration of bitartrate (HT-) exists at pH 3.6. At such pH, there is much available substrate to bind with K+ to form the KHT product. As a result of KHT precipitation, the titratable acidity will decrease. However, changes in pH are a result of the initial pH prior to cold stabilization. A direct relationship between pH value and percentage of HT- occurs. 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. If the initial pH is above pH 3.6, then the pH will increase as KHT precipitates out of solution (Iland 2004)."

EDIT: If you'd like to read the whole article, you can here: http://extension.psu.edu/food/enology/analytical-services/cold-stabilization-options-for-wineries
 
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Boatboy24

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Sorry for all of the chemistry talk below. The referenced chart didn't come through in the cut/paste, but the information about the pH reaction to CS in the last paragraph is the important part........
Here you go:




I updated my post - should have mentioned that K-carbonate, followed by cold stabilization is what will work. But go slow - you probably need only half of what most formulas say you need.
 
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DG2001

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Just so I'm clear on this. First I add calcium carbonate or potassium carbonate to lower TA and raise pH, then cold stabilize to precipitate salts. That right? Does it matter if I use potassium or calcium? Also is there any need to do it now opposed to a week or two before bottling after bulk aging?
 
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Boatboy24

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I'm only familiar wit the process using Potassium Carbonate. After that addition, you need to cold stabilize for at least two weeks. The formula I have is 1g/L to bring pH up 0.1. However, in my experience, you will overshoot more often than not. Start with half that amount and see where it gets you. Then repeat if necessary.
 

Johny99

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John has the whole pH tartrate precipitation relationship right.

One other thought since I'm not a huge fan of the side effect of potassium carbonate, if you have something to blend you could cs, blend and cs again. Also, pH is about stability, TA is more of a taste effect. You could CS and then look at adjusting with KCO. Counter to that idea is that I do remember reading someplace that the potassium will help seed the cs participation. Me, I'd go in steps and taste a lot.
 

Johnd

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For small adjustments in finished wine, under 1 g/L, I just use potassium bicarbonate. The wine typically sits in the cellar in bulk at 55F for many months prior to bottling, so a small amount of precip may occur, but the pH holds just fine. Once bottled, it's still stored at 55F, I've not had any additional precipitation in bottles. Go slow and taste along the way if you decide to raise the pH with K bicarbonate.
 

Johnd

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As would I, since I've used it on my low pH Chileans from last year and have experienced no side effects.
 

GreginND

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If you use calcium you will need to age for longer. It takes a lot longer for calcium tartrates to precipitate. Plan on six months or more.
 

fafrd

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Here you go:




I updated my post - should have mentioned that K-carbonate, followed by cold stabilization is what will work. But go slow - you probably need only half of what most formulas say you need.
Does this graph hold true even for CS without any additions, or only in the case the calcium carbonate is added?

Since other posts have indicated that the taste of the wine is primarily tied to TA rather than pH, what is the downside to having a low pH wine drop pH further if TA was reduced?

Lile the original poster, I have an overly acidic red wine (TA=0.79%, pH=3.25).

It tastes too tart and I want to try to drop TA by 0.1-0.15%.

If I try CS alone, is that likely to drop TA close to my target ampunt? If pH decreases rather than increases, does that cause a problem? (lower pH is better for stability).

If I go the route of adding potassium bicarbonate and do not CS after, is the only downside the possibility of some crystal formation if the wine gets chilled after it is bottled?

If the most effective way to reach my TA reduction targets is to add Potassium Bicarbonate followed by cold stabilization, will the cold stabilization further drop TA or can I assume the TA after adding Potassium Bicarbonate is where TA will end up and the CS is merely to avoid the possibility of any crystal formation post-bottle?

I've got enough wine that I can afford to try a few different options (including blending with an average-acidity wine) on bench trials before deciding what to do to the main batch - any suggestions appreciated.
 
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Johny99

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I'd suggest CS first. Then taste. Numbers are good but taste and aroma are all that really matter. To me the bicarbonates flatten the wine and strip aroma. Could just be my bias, well ok likely is. :? I'd go for blending to taste after CS.
 

fafrd

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I'd suggest CS first. Then taste. Numbers are good but taste and aroma are all that really matter. To me the bicarbonates flatten the wine and strip aroma. Could just be my bias, well ok likely is. :? I'd go for blending to taste after CS.
It's not really a numbers thing - I was happy with the numbers until the wine started tasting too tart as the tannins mellowed.

'flatten the wine and strip aroma' makes it sound as though you have tried bicarbonate and were not happy with the outcome.

I'm in no rush and will spend a few bottles of wine on some bench trials:

-control (do nothing)
-CS
-bicarbonate w/o C/S
-bicarbonate followed by CS

Any experience as to the approximate TA reduction that can be expected from CS alone?
 

Johny99

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I think your trials look good. Do report back how they compare. The TA reduction depends on a bunch of different things; pH, levels of different acids, potassium level, temperature and saturation level, etc. that the change is hard to predict.
 

fafrd

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I think your trials look good. Do report back how they compare. The TA reduction depends on a bunch of different things; pH, levels of different acids, potassium level, temperature and saturation level, etc. that the change is hard to predict.
Will do (report back).

I ran into this article in case anyone is interested in geeking out on this subject: http://www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Potassium Bitartrate Stabilization of Wines.pdf

Towards the end, they show an example where cold stabilization refuced TA by 0.3 g/L (0.03%) and pH decreased by 0.08...
 

fafrd

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I'd suggest CS first. Then taste. Numbers are good but taste and aroma are all that really matter. To me the bicarbonates flatten the wine and strip aroma. Could just be my bias, well ok likely is. :? I'd go for blending to taste after CS.
Found this on the same subject regarding CS: http://www.winegrowers.info/wine_making/Cold stabilisation.htm

"Some winemakers argue that a portion of the flavour and uniqueness of the wine is lost with the crystals."

Seems as though I'm just going to have to try these different techniques out and figure out for myself what works best for this overly-acidic Merlot...
 
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