A tale of acid, MLF, and What do I do Now?

Dan - Did you degas your samples before measuring TA and pH. Wine samples taken during fermentation will be full of CO2 and this will give you false results unless you heat the sample to boil off the CO2 and then replace the lost volume with distilled water.

Bill Frazier Olathe, Kansas USA

Dan, I would agree with Bill, degas and remeasure.

Measure out either 50 or 100 ml of must or wine.

Heat in microwave until boiling.

Cool back to room temperature.

Add distillled water back to 50 or 100 ml.

Calibrate the pH meter.

Measure both TA and pH.

I use 10 ml for the sample and use 0.1 normal NaOH. You can check the NaOH with Potassium Acid Phalate to get the actual normality and use Bens formula, that is what I do.

Hope that helps.

Joe

No, I didn't de-gas before measuring during fermentation. Which way does the CO2 effect readings for pH and TA - higher, lower?

The question still remains - what do I do now? Can I raise acid with tartaric post fermentation and MLF without bad consequences?

thx dan

Daniel Tortorici wrote "No, I didn't de-gas before measuring during fermentation. Which way does the CO2 effect readings for pH and TA - higher, lower? The question still remains - what do I do now? Can I raise acid with tartaric post fermentation and MLF without bad consequences?"

Dan - I think the question is...how confident are you in the post ML numbers. Your acid numbers seem pretty good. The pH is high.

5 Days of MLF lead to the following numbers: Cabernet TA 0.5 pH 3.97 Zinfandel TA 0.65 pH 3.86 Merlot TA 0.64 pH 3.72

I bet there's still some CO2 in solution that's affecting your pH and TA measurements. Before I would consider adding anything to the wines I would degas, retest and evaluate the wine flavor. In the end the real question is; how does the wine taste.

Bill Frazier Olathe, Kansas USA

Bill, Thanks for the suggestions. When I get back home this weekend I'll degas and retest as you suggested. As for taste the Cab is a little flat otherwise the others seem fine. dan

I think TA reads too high if you don't degass the sample after fermentation starts. If your cab tastes flat, I'll bet your recalculated pre-fermentation numbers were closest to being the accurate ones (at least up to the point of doing the MLF).

A related question on degassing - I noticed that you should add distilled water after degassing to get it back to the original volume. Why is this?

dan

Hi Dan,

Because if you loss water by boiling it off, you're changing the concentration of the acids (same # of g of acid divided by fewer mL of water).

I actually haven't found it to be a huge difference. I just bring the wine to boiling, and find that after cooling the volume is only down by 4 ml out of 100. A 4% error doesn't bother me any.

Do the rest of you find that you lose more water than that? How long are you boiling?

Dave

**************************************************************************** Dave Breeden snipped-for-privacy@lightlink.com

David C Breeden wrote "I actually haven't found it to be a huge difference. I just bring

by 4 ml out of 100. A 4% error doesn't bother me any. Do the rest of you find that you lose more water than that? How

Dave - I use anywhere from 200 to 400ml for a sample. I put it on the stove in a covered pan, heat to a boil and then simmer for 10 minutes while I do something else. Even tho. the pan is covered I boil off about 25% of the volume. So, I have to qs back to starting volume or my test results wouldn't mean anything.

Here's some recent data showing why you have to boil off the CO2 to get meaningful results. This data is for my 2004 Chambourcin/NY73 wine just after yeast fermentation completed and before I added the ML culture;

Before CO2 removal - pH 3.48, TA 1.22% After CO2 removal - pH 3.24, TA 1.04%

Bill Frazier Olathe, Kansas USA

Thanks, Bill!

Hmmm. Maybe I'm not boiling long enough?

I've had similar results to yours above. Can anyone explain why, if you boil off CO2 (an acid. a non-protic acid, granted, but an acid) the pH goes DOWN?

How long are the rest of you boiling? I thought I remembered Tom S. saying that he would bring the wine just to a boil.

Dave

**************************************************************************** Dave Breeden snipped-for-privacy@lightlink.com

David C Breeden wrote "Can anyone explain why, if you boil off CO2 (an acid. a non-protic acid, granted, but an acid) the pH goes DOWN? How long are the rest of you boiling? I thought I remembered Tom S. saying that he would bring the wine just to a boil."

Dave, I should have added that the juice, prior to yeast fermentation had these numbers; pH 3.37, TA 1.01%. After fermentation and before adding ML culture the numbers were as follows;

It's my understanding that addition of distilled water, which theoretically contains no ions, should not affect pH (it doesn't seem to affect TA). I buy the distilled water from the grocery store in plastic bottles. I doubt it's as pure as that used in a laboratory and this may be part of the reason for the pH shift. Also, during fermentation acid composition of wine changes and this may affect pH.

Hi Dave, Carbonic acid is a very weak acid. Very few molecules are ionized so I don't think CO2 removal would change the pH much one way or the other. Lum Del Mar, California, USA

Two things:

First, distilled water (at least if you buy it off the store shelf) usually is not pH 7. It reacts with CO2 in the air and becomes somewhere between 5.6 and 7.0 from what I've read. Tested some from a freshly opened jug here at work once and it was a ways from neutral - don't remember the measurements now.

I guess it could be easily adjusted to 7, but would this affect the Ta reading?

Second, shouldn't your pH have went up after boiling, Bill?

Miker wrote >

Yes Miker, it seems like the pH should have gone up. Maybe stay the same but not go down. Back when I worked in a pharmaceutical lab you would stick a pH probe in distilled water. The pH reading would wander around and never settle. That was very good quality distilled water and the pH readings were what I would expect. I don't expect the same result from grocery store distilled water but it should be better than what I would experience with Johnson County, Kansas tap water. The pH of our local water is near 9 because of addition of chlorine, chloramine and slaked lime.

I'll give a try to grocery store reverse osmosis water and report back.

Bill Frazier Olathe, Kansas USA

Interesting. I understand why the TA goes down, but why does the pH drop too - anybody knows? I think Joe reported the same thing in another thread.

Pp

Guess I need to find a faster way to post to this newsgroup than through Google. My first post hasn't shown up yet as I write this several hours later. I already see that you have addressed my two points already, Bill. It will probably look like I wrote my comments after seeing your explanations but it just happens that you addressed both of my points before my first post could show up. As you say, your pH may have been lowered by the distilled water. Whether it affects TA, I'm still not sure.

Miker