Pre-Fermentation Acid Addition -- Unusual Case

 

This being harvest season, I thought I'd share a typical consulting conversation. I taught for 24 years a class at the UC Davis Extension called "Fundamentals of Wine Chemistry," and this is a former student's question which encapsulates many nuances of must correction principles which may be of interest to commercial winemakers and home enthusiasts, and may offer for general readership a glimpse into real life winemaking.

Clark,

We took your “Fundamentals of Wine Chemistry” class last fall, and have a question. We just picked up some Viognier from Paso Robles with 3.5 pH and .5 TA; we have not started fermentation yet.

We’re thinking we want to raise the acid a little. In looking over my notes, I see that you gave an example of a Yolo Semillon that had the same specs, and you said the WRONG thing to do would be to add tartaric. You recommended adding 2g/l of malic acid instead, since adding tartaric would result in too low of a pH. 
Unfortunately, our notes from the class did not list the malic component of your example.
Our goal is to capture the wonderful aromas of a traditional Viognier (and hopefully achieve good balance) with a cold fermentation at 50 F.

(the complete specs at harvest are brix=26.5, TA=0.5, pH=3.5, NH3=38ppm, AH=76ppm, YAN=114ppm, malic=2.19g/L, tartaric=4.64g/L, K=1789ppm, VA=0.013g/100mL)

We’d GREATLY appreciate any advice you have!! Thanks!

[Name withheld]

My response:

Go to the head of the class. You are exactly right, and you have avoided the disaster of an extremely low pH, perhaps 2.85 as in my example in 1986. The problem, which is common for German wines, is that at this pH, sulfur dioxide is very volatile, even at very low levels, so it interferes with the nose unless you use so little that you risk having none at all, in which case the wine may brown as did my Semillon.

Be sure your numbers are correct, and then adjust the TA with maybe 1.5 g/L using malic and see where you end up after fermentation. Because it’s lighter, you adjust with less; the ratio of the molecular weights is 0.893, so you really add 1.34 gm/L malic acid to achieve a boost of 1.5 gm/L in the TA.

The combination of this acid add and the precipitation of KHT should lower your pH to a good place, maybe 3.35 and 6 gm/L. That’s probably still too low a TA for you, but will give you a nice healthy fermentation and you can see how you like the result. Depending on how crisp you want the wine, you’ll probably want to finish with 6 – 7 g/L and a pH around 3.2 – 3.4. (I'm assuming no malolactic.) Depending on where you are, adjust further with malic or tartaric, bearing in mind that cold stabilization will further lower the pH and also the TA, and more so if you use tartaric.

Before you taste, it’s best to wait a few weeks for the hotness of freshly added acid to abate before you decide on further adjustments.

Congratulations on your excellent recall.

Clark

 

musings: 

Comments

 

 

Irving So:

This is fascinating. Most textbooks seem to suggest adding tartaric and lactic rather malic, and that tartaric usually has a stronger buffer capacity such that the pH will change little on addition (assuming no cold stab). Am I totally out of line? Will adding malic give too much of an appley flavor to Viognier?

Dear Irving:

Good questions. I don't know how to answer them without getting pretty geeky. If your chemistry isn't up to this explanation, you'll want to go find a chemist or get back to me with more questions.

First, it's essential to understand that KHTa, the potassium bitatrate half salt, precipitates from alcoholic solution, whereas malic (or lactic) salts do not, but rather stay in solution. Since KHTa contains a titratable proton, the effect of this preciptiation is always to lower TA (tartness). In high pH wines (above 3.6), pH rises when this happens, as you might expect -- less acidity, right? But in wines below 3.6, while the TA goes down, the pH ALSO goes down. If you lack malic (or lactic) to buffer this change, it is possible to end up with unmanagebly low pH's as I did.

It would work fine from a numbers point of view to use lactic instead of malic, but it tastes different. Lactic is not creamy in taste, but hot on the mid back palate, almost like jalepeno, somewhat similar to acetic, which is very piquant in the finish, but not as tangy and not as far back. Malic doesn't taste like apples. It has a crispness which is tasted in the front to middle mouth, while tartaric is further up front.

Your statement that tartaric has more buffering power, and therefore shifts pH less, is false. We say tartaric is the strongest acid you can add to wine, and gives you the most pH bang for your TA buck. Tartaric buffers in the 3.0 range. Malic buffers in the 3.5 range, lactic in the 3.8 range, acetic in the 4.8 range. The best wines have a good ratio of these acids, resulting in a blended, almost linear buffer curve and a broad and balanced flavor expression.

California wines (and certainly European wines) tend to benefit from tartaric addition for its ability to lower pH without affecting TA as much. But in this one unusual example, the pH is actually already too low for the TA of 5.0, so this effect is undesireable, and the odd choice of malic is the best.

 

 

 

Dear Name Witheld-
Perhaps you had no control over picking decisions? If this wine had been harvested earlier, while acidity was higher, and before sugar got so high, and fermentable nitrogen so low, you may have had the option of making a balanced wine without additions, or fewer. Less is more. If you don't have to decide how much water, acid, etc. to add, because the juice is naturally balanced, there's much less work, less chance of screwing up, and possibly even a better wine that reflects the nature of its origin, not the nature of your additive manufacturer. If you are a certain sort of winemaker, though, that might be where all the fun is- the technical ins and outs of manipulation. If one has a fermentation science degree, one probably wants to use it. Simply wandering around vineyards all day, doing juice sample analysis, and then picking balanced juice that sort of makes itself, doesn't allow for much "winemaking". I don't buy the story that grapes have to taste like Grandma's jam or Jamaican beach drinks before they can make good wine. I've made, and tasted other makers's varietally correct viogniers (floral and peach aromas) that were made from grapes harvested at 23 brix. Of course, I've also tasted some that were picked too soon, overcropped, or grown in the wrong place, that tasted like bad sauvignon blanc. Good luck with your viognier, and have fun calculating those adds. L-malic, or D-malic?

Dear Mark:
From your logic, most of Bordeaux and Burgundy are grown in the wrong place, requiring as they do beet sugar additions to the Premier Crus wines in most years. Perhaps they will benefit from global warming in bringing their regions into your politically correct balance. Personally I prefer my chef to salt the soup if it needs it, and I don't find this destroys its flavor if done with skill. My favorite corollary of Murphy's Law is "Nothing is impossible for the man who doesn't have to do it himself." I know that you are too good a winemaker than to subscribe to a braindead hands off philosophy wholesale, and you also know me better than to think I use tools for tools' sake. That said, we all believe in doing less when we can. As Einstein put it, things should be done as simply as possible, and no simpler.
Thanks for the input. Iron sharpens iron.
Clark

 

 

 

Clark
I have to make additions every year. I wish I didn't, but as you point out, it ain't a perfect world, even in France. I'm not a fire-breathing non-interventionist. I am rational, and, above all, want to make balanced wine that tastes good. I do practice what I preach, however, even when it gets a little scary. I have made a handful of wines with no adds whatsoever. I'm a little scared of bottling a commercial wine without sulfite at bottling. I don't have a good enough understanding of the forces at work, and I've bought a few pretty funky sultfite-free wines. We just started our own label, so I'm not playing with someone else's money, either. I admit that my screed was a little too simple-minded, but the point got made. After being in Virginia, where sometimes you are forced to practically manufacture a wine because the raw material is so compromised, it just hurts my soul to see winemakers take this wonderful California fruit and start throwing shit into it. I really appreciate this blog- I don't know where else I could get all this info, this dialogue, and read about concepts and ideas so fundamental to understanding the winemaking process. Keep it up, and keep sticking it to me. A valid, well-considered opinion must be able to withstand criticism, and also be able to integrate new knowledge and ideas. Mark