ph during fermentation

[Dewbie]

Got a new ph meter for Christmas. Have been making Concord grape wine, kits & dandelion wine for years Ignoring acid levels. Started my first batch of dragon blood over the weekend. SG 1.102 ph3.55. Used EC1118. Today after stirring, SG is 1.062 & ph2.98. Was surprised in the change in ph. My question is do I adjust the ph now while it’s still working or wait until fermentation is almost done? If I adjust now I’m wondering how it will effect the taste of the finished product?

 

[winemaker81]

Don't mess with the pH during fermentation. Carbon dioxide forms carbonic acid, which can temporarily lower the pH.

It's also worth it to check that your meter is properly calibrated

 

[BernardSmith]

Here's the thing: Yeast really dislike a pH much lower than about 2.8. But a pH much above 4 is not very hostile to bacteria you don't want. But the dirty little secret is that pH is a measure of the strength of the acids in solution and the fact is that while we can taste different acids (tartaric does not taste like malic and malic does not taste like citric) we are unable to taste acids by strength. What we taste is the AMOUNT of acid dissolved in solution and the MORE acids the more acidic the wine will taste which is why BEFORE bottling (after fermentation and degassing is all finished) we measure the TA (titratable acidity) . If a wine tastes bland, that suggests the TA is less than about .6g/L of acid in solution. If it tastes bright and zingy, then it probably has enough acidity. If you are looking for a a way to measure the TA you can use your pH meter. and you measure a sample of wine to which you have added drop by drop Na OH until the pH meter reads 8.2. The amount of Sodium Hydroxide you needed to add to hit 8.2 can be converted to indicate the volume of acid in solution.
After fermentation, the pH has a value in enabling you to determine how much K-meta to add to inhibit oxidation. The stronger the acidity (the lower the pH) the less free sulfur you need to inhibit oxidation at bottling. But many home wine makers simply add the equivalent of 1 campden tab /gallon to provide about 50 ppm of the sulfur.

 

[BigDaveK]

Like @winemaker81 said, don't mess with pH during fermentation. Lots of complex reactions going on.

I will amend one thing he said, though. (Sorry Bryan - too much reading.) Carbonic acid is formed but it's highly unstable and almost instantly ionizes. However, "pH" stands for the "power of Hydrogen" and it's a measurement of hydrogen ions. During fermentation yeast will actually produce hydrogen ions causing a change in the pH reading, usually temporarily. I've had fermentations hit 2.7 a couple times and even 2.6 once, but everything settles down and they finished over 3.0.

Low pH is good for a couple things - shifts color to more red, enhances production of fruity esters, increases aging potential, and of course it's great protection against bacteria. And it compliments SO2 - high pH you need more, low pH you need less. Also, some yeast will produce more alcohol with low pH. Not a lot - the ABV may increase 1/2 to 1 %.

 

[Raptor99]

Don't mess with the pH during fermentation.

I would add, that sometimes you need to adjust pH before fermentation. Then you might need to adjust TA after fermentation, before bottling. But don't try to adjust it during fermentation.

 

[winemaker81]

I will amend one thing he said, though. (Sorry Bryan - too much reading.) Carbonic acid is formed but it's highly unstable and almost instantly ionizes. However, "pH" stands for the "power of Hydrogen" and it's a measurement of hydrogen ions. During fermentation yeast will actually produce hydrogen ions causing a change in the pH reading, usually temporarily. I've had fermentations hit 2.7 a couple times and even 2.6 once, but everything settles down and they finished over 3.0.

I've read several sources that attributed the pH change to carbonic acid, hence my comment.

The pH dropping is a common statement. Regardless of source, it often drops, then raises again. Assuming your source is correct, if carbonic acid forms and breaks down constantly, the pH can have a steady curve downward, then later upward.

In any case, the consensus for @Dewbie is "Don't mess with the pH now".

 

[BigDaveK]

I've read several sources that attributed the pH change to carbonic acid, hence my comment.

Assuming your source is correct,

You're absolutely correct. I've come across a lot of conflicting information and try to find corroboration. Only have one here:

 

[winemaker81]

@BigDaveK, this line on the second page is interesting: "It is most soluble in solvents such as ethanol and acetone which contain both hydrophobic and strongly polar groups." It may explain why we can have a lot of what appears to be CO2 in a wine, during and and post-fermentation.

I once made the mistake of giving wine in a 19 liter carboy a vigorous stir -- it was down about 3 to 4 bottles, plenty of room, right?

Ahhh ... no. I didn't lose more than 4 or 5 oz of wine, but "purple volcano" I've mentioned previously? It was mostly bubbles. I wish I had video of it!

It appears you misinterpreted one thing -- the acid is slow to form and slow to break down, but it ionizes instantly. This causes a drop in pH, although I didn't find any indication of how significant the drop may be.

At first I thought the last paragraph states that carbonic acid doesn't exist below pH 8, which is not true. Upon re-reading, one ionized form doesn't exist, but apparently the other does. The nuances push the boundaries of my memories of Chem 101/102 from 30+ years ago ....

 

[Rice_Guy]

pH 3.55. . . . I’m wondering how it will affect the taste of the finished product?

Once you have degassed you should expect the pH to be back to 3.55 +/- 0.1 unit.

 

[stickman]

I know I've said this before, but TA is definitely affected by co2 content, so conducting a TA titration with co2 present will cause an error on the high side. Degassing the sample is good practice as the pH probe may be affected by CO2 bubbles etc., but it should be pointed out that pH is not significantly affected by co2 unless the initial must or wine pH is above 4. Carbonic acid has two pKa's, the first is 6.37 and the second is 10.32, so when the wine pH is 4 or below, little to none of the co2 (carbonic acid) is dissociated and therefore doesn't contribute significantly to the pH.

 

[Dewbie]

Thanks to all for this tremendous amount of information. I‘ll re-calibrate my ph meter. I will not adjust ph until fermentation is complete - if needed. I will check sg & ph daily for historical reference. I’ll test TA before bottling. I’ll post the results.

 

[rsportsman]

I know I've said this before, but TA is definitely affected by co2 content, so conducting a TA titration with co2 present will cause an error on the high side. Degassing the sample is good practice as the pH probe may be affected by CO2 bubbles etc., but it should be pointed out that pH is not significantly affected by co2 unless the initial must or wine pH is above 4. Carbonic acid has two pKa's, the first is 6.37 and the second is 10.32, so when the wine pH is 4 or below, little to none of the co2 (carbonic acid) is dissociated and therefore doesn't contribute significantly to the pH.

The first pKa of 6.37 is an apparent pKa for the overall reaction H2O + CO2 <==> H2CO3 <==> H+ + HCO3- . The actual pKa for dissociation of carbonic acid H2CO3 is much lower, on the order of 3.5 - whether this is significant in most wine is not clear.

 

[rsportsman]

Thanks to all for this tremendous amount of information. I‘ll re-calibrate my ph meter. I will not adjust ph until fermentation is complete - if needed. I will check sg & ph daily for historical reference. I’ll test TA before bottling. I’ll post the results.

You can check your pH calibration with saturated cream of tartar https://vinmetrica.com/troubleshooting-guide/#CreamOfTartar