The trouble with my ZIN (high pH)

Alex wrote "I bought some Zinfandel grapes from Brentwood CA. The grapes were at 24 brix but by the time I got over there and picked them they shot up to 26 brix. So I made wine anyways: pH 3.82, TA 7, SG 1.110 or 16 brix (best I can read from my cheap hydrometer)

-Alex, did you do the tests to arrive at the above numbers? BTW 16 brix is about SG 1.066. You added 84 grams tartaric acid to 50 gallons of must (38gallons juice). Like you say this works out to 0.58 grams per liter. The total acid in your juice is now 7.58 grams per liter or 0.76%TA. This probably was not enough acid addition to drop the pH much. I usually hang a pH probe in the juice or wine. Calculate the maximum acid I dare to add. Then add acid up to this amount with good mixing watching the pH drop.

The wine smells good....but there is definitely some heat from the alcohol and slight but not over powering tartness from the acid.

-I'm not surprised at the alcoholic heat. But if you want to taste over powering tartness from excess acid come to Kansas City and work with must containing 0.9% TA.

Clyde Gill has a good laboratory method to determine how much acid addition is required to drop pH to a desired value. He might be busy right now at the winery so if he doesn't chime in I can post his method. Since you have access to lab equipment you could try his method. If you want to get that pH down to a reasonable number I think you will have to add tartaric acid and then drop it out with a hard, cold conditioning later on.

Bill Frazier Olathe, Kansas USA

The 16 brix is a typo I meant 26.

-Alex

Those numbers aren't really that bad. I recently read an article in a trade magazine on picking at optimum ripeness. They were mainly talking about Syrah, but this sounds good for Zinfandel too. One of the winemakers was quoted as saying, "26 [Brix] is the new 24."

I'd recommend that you try to get the pH to ~3.6 or so _after_ ML and cold stabilization. To do that, you need the ML to finish first. Then do bench trials on the wine, adding 1g/liter, 2g/liter and 3g/liter to three samples. Chill the wine to nearly freezing, until the bitartrate all drops out. This can take as long as a couple of weeks. Decant the wines from the bitartrate sediment, let them warm to cellar temperature and taste them, both with and without food. See which you like best. Measure the pH if you like, but it'll probably end up around 3.6 to 3.7 in the sample that tastes best to you. Don't worry about the TA. That'll take care of itself.

Once you determine the correct addition (which could be somewhere in between those numbers) scale the tartaric addition up for the whole batch. Get one or two people who are better at math to check your numbers before you commit the entire lot or you may end up back here asking how to do acid reduction! You'll have to cold stabilize the entire lot, but you could actually wait until after barrel aging to do that if you wish.

Tom S

Tom, Thanks for the advice... sometimes the obvious escapes me like testing small batches. Would a 750ml bottle be large enough of a sample or should I use 1 gallon samples to treat and cold stabilize? How do people cold stabilize their wines if they don't have a temperature controlled room? I do have access to a 4 degree Celsius room at my lab and I could probably fit SS beer kegs of wine in there without anyone getting upset with me, I only have 38 gallons, so I could do it in two kegs. How quickly do you have to transfer the wine off the crystals before they dissolve? I would prefer to take the kegs home and not make a mess in the lab if it won't hurt anything. What happens if I do nothing? Thanks, Alex P

Hi Alex, That pH seems awful high for a TA in the range you are talking. That sounds like a good Fisher Scientific or Corning pH meter, but are you calibrating it right before the measurement and are you degassing the sample? If so are you sure of the normality of your NAOH? If it tastes tart the TA seems right...

I take the sample to boiling for an instant prior to reading. CO2 can make the pH seem falsely high.

The right way to do it is to measure out at least 50 ml of sample, degas, add distilled water back to 50 ml if necessary, cal the meter, measure pH and titrate acid.

Joe

William Frazier wrote "Clyde Gill has a good laboratory method to determine how much acid addition is required to drop pH to a desired value. He might be busy right now at the winery so if he doesn't chime in I can post his method."

Here's Clyde's method. Since your wine is fermenting it probably won't be possible to do this until it's dry so CO2 doesn't interfer with the result. I think Clyde uses this method for juice before fermentation.

Make a tartaric acid solution (Dissolve 2.0 grams t.acid in enough distilled water to make 200 ml. The solution contains 0.01 gram per ml) Measure out a specific volume of juice or wine (Example 50 ml) Put a pH probe in the juice or wine. Add the t. acid solution to the sample until the pH drops to the desired level (Clyde says pH 4.5 is ideal for juice that will make a red wine) Calculate how much t. acid is needed for one gallon (3785 ml) juice or wine (volume of t.acid solution used x 0.01 = grams t. acid required for the 50ml sample) (3785ml / 50 ml = 75.7 x grams t. acid required for the sample) Multiply the result by the number of gallons of juice or wine you want to treat

I would still stick a pH probe in the bulk juice or wine and add tartaric acid slowly with good mixing.

Bill Frazier Olathe, Kansas USA

Joe, I did calibrate the meter just before use and I made up the .2 M NaOH from a 5 M stock that is only a few weeks old. I am not so certain I properly degassed the wine though. I had it in a 50 ml conical tube and microwaved it until it was hot (not yet boiling) and I saw a bunch of bubbles forming on the side of the tube. I then put 15 ml in a flask and swirled it around for a while and waited for it to cool off before I checked the pH and titrated the acid. I will definitely re check it, but if nothing terrible will happen to the wine in the short term I will wait for fermentation and ML to stop completely. There is still an occasional bubble coming out of the air lock.

In case I get anxious or for next time , can the wine be degassed properly by putting it under a vacuum or bubbling nitrogen through it? I have both of these readily available and maybe it would be more certain than just heating it up?

Alex, Your process was pretty good, the only thing I would do differently is make sure I still had 50 ml after the heating. Add distilled water if necessary, then pull the sample.

Vacuum degassing or purging with nitrogen may work, but I'm not a chemist so I can't say with certainty. Margalit suggests the heating process you used, but uses a 100 ml sample size. His book Winery Technology is great and under $30 US. Mine is pretty worn out.

You seem to have a lot of potassium in that must. The ratio of malic falls and tartaric rises (since it does not fall) in mature grapes. Adding tartaric as Tom and Bill suggest will pull the potassium out and swing the pH better than malic so I would do that too. You really do want to cold stabilize. 25 F is faster than 40 F, but winter is coming and that could be an option too.

I'm not as experienced as Tom and still measure and use TA. It's easier to understand and manipulate for me since the relationship is linear, not a log function like pH.

It's also easier for me to correlate taste to TA than pH, I have never had a dry red with a TA over 6g/l that I thought was balanced. It's always too tart for me. OTOH I've had the pH all over the place (from

3.45 to 3.85) on wines I like with a TA under 6 and that's a big difference (to me).

Taste is everything though, trust your taste over optimal values in a book. The author is not drinking your wine...

:o)

Joe