Acidity, PH, & TA: OH My!

I have written previously that wine yeast has no desire to make good wine. These organisms only follow nature’s playbook: They just want to make more yeast organisms! So too, wine grapes also have no interest in making good wine: They just want ripe seeds! Both these organisms are seeking to reproduce and it is we humans who want to capture that process for our own purposes: We want to make great wine!

At the core of these processes are acids, mostly tartaric acid. Grape vines want to keep their fruit too sour to eat until their seeds are just ripe enough. Yeast also works best at certain acid levels. So too, we wine drinkers want our wine to be within certain levels of acidity.

For us winemakers to master the winemaking process, we must understand that at wine’s core, its backbone, is the acid structure of the wine. Making this learning curve more difficult is that acid structure must be appropriate to the particular grape varietal and the particular growing season. It needs to reflect the style, color and body of the varietal. A flabby, low acid, Riesling would be a winemaking crime.  A very acidic, tannic, high alcohol, red wine would be a train crash in your mouth. To make a good, balanced wine, a good winemaker needs to understand what acids are in wine, how to measure them, how to know what amount is appropriate, and how to adjust them to create a good finished wine. This article will discuss how to do just that.

What is Acidity?

The word “acid” comes from the Latin word meaning “sour.” Acids have a PH less than 7 and in solution donate a hydrogen ion (H+). Acid can be strong enough to melt metal, or weak enough to be pleasant on your tongue, like lemon juice on your fish.

Humans seem to be drawn to acidic beverages, perhaps from the dawn of time. Maybe it is a biological trait which helps us to survive. Acidic beverages tend to have vitamins we need to avoid ailments like scurvy. Whatever the biological need, many of our favorite drinks, like colas, lemonade, and of course wine, contain acids. Each of our individual palates tolerates or enjoys acid in different strengths.

We can perceive acids in our mouths, which affect how we taste. In the mouth, acids stimulate our saliva glands, or more politely put, it makes a food mouthwatering. They also make food easier to taste and enjoy. Perhaps it’s like salt, magnifying flavors. I enjoy a vinaigrette on a fresh salad. I also find that a little vinegar added to a chili can help make the flavors pop. All of this from a donated hydrogen ion.

But unlike salt, acids also have a flavor profile. As well as having different strengths, acids add to the flavor profile of food and especially wine. Malic acid, like the acid in a green apple, is essential to wines like Sauvignon Blanc and Riesling. Substituting more tartaric acid for malic acid in these wines would change them fundamentally. Reversing that, substituting malic acid for tartaric acid in a Cabernet Sauvignon would be unpleasant, which is why most red wines undergo a malolactic fermentation.

One of the most important skills for any winemaker is knowing what perfect balance should be, and being able to obtain that balance, up or down, without altering the grape varietal’s character. A good winemaker knows when it’s better to mask acids in a wine, rather than adjusting them.

Getting the Balance Right

There’s no recipe for making wine that consistently works, because no two vintages are exactly the same. There are guidelines that can help you find your way, though. These guidelines need to be applied with some appreciation as to region the grapes were grown in (cool vs. warm or hot) and also the grape varietal you are fermenting. Thus you first you have to know the amount of acids in the grape must and determine their relative strength. To calibrate these acids two standards are used. These are called TA and PH.  

TA is shorthand for “titratable acid”, sometimes called “total acid.” This is a measure of the amount of acid in the must or wine, but not necessarily the strength of the acids. In grapes the majority of the acid is tartaric acid. This is a unique feature of grape juice, as most other fruit lacks tartaric acid and is a mixture of other acids, malic acid being foremost.

TA in white wines, generally, should have more acid than red wines and a TA range of between 6-9 g/L (grams per Liter). For instance, I like a racier Chardonnay and I like a TA of 7- 8g/L when I make Chardonnay. A California style Chardonnay might have 6-7g/L. Riesling or Sauvignon Blanc may be 8-9g/L. 

For red wine, where tannins and the acid in the wine clash in the mouth, a lower TA is suggested at 6-7g/L. Pinot Noir, I think, can show well with a bit more acid as it is a thin skinned varietal with less tannin in the skins. Big California reds are usually on the lower end of the TA red wine range.

But TA is only one of the two measures. PH, short for “potential hydrogen” (remember that hydrogen ion) is the other. PH looks at the strength of the acids over all. This is very important to a wine’s ability to avoid oxidation and spoilage and how much SO2 to add. White wines are usually 2.5 to 3.5 PH and reds at 3.4 to 3.7 PH. Again, aromatic whites tend to be on the low end, with 3.2 a general sweet spot (in my estimation) and big reds at 3.5 to 3.6.

There are two PH numbers to keep an eye on. One number is 3.2 PH, because some yeasts struggle with lower acidity levels and malic bacteria (malolactic fermentation) may also refuse to start at that or lower levels. Both are cured with a tolerant yeast strain and malic culture designed for high acid varietal fermentations.

Another PH number to be careful with is a wine over 3.6. Wine becomes chemically unstable over that PH level. Unusual chemical reactions can occur at high PH levels. Also the amount of SO2 required to keep the wine from spoiling above 3.6 becomes astronomical.

Keep in mind also, that PH measurement can vary throughout a fermentation. At the crusher the various lots of grapes can have slightly different PH due to ripening variances. It’s surprisingly hard to amalgamate the batch. So, you may not have a true reading. Also, with cold soaking and fermentation, potassium will leach from the grape skins into the must altering the PH of the must upward.

If in doubt, consider taking the middle road on your target TA and PH numbers or be conservative in your adjustments as you can do an “acid polishing” after fermentation. One thing to consider avoiding is over-adjusting a wine. It can lead to a “Frankenstein” wine. Sometimes the terroir needs to speak, even if the numbers are not perfect.

Getting the Numbers

Besides TA and PH, a good winemaker must cultivate a “winemaker’s palate”. Taste can help lead a good winemaker to understand the correct balance of acids in the wine and it is taste that tells a winemaker whether something is right or wrong with the acid balance. A good winemaker makes sure their taste buds are properly calibrated.

PH is the easiest metric to discover. PH meters are very inexpensive these days. But they must be calibrated to give a correct reading. That may be the difference between a cheap PH meter and one you will want to use. It’s worth it to have a meter that is easy to calibrate, as I find myself checking and recalculating often, especially if I am processing multiple batches of grapes. It’s also worth it to have a meter that reads in two digits after the first number. For instance 3.60, 3.65, etc. versus one that only gives a number like 3.6 and 3.7, with no numbers in-between. For SO2 additions, that difference is a big deal. 

You will need a PH calibrating solution, one at PH 4 and one at PH 7. To calibrate, follow the manufacturer’s instructions. Thereafter, you can immerse the meter in the must or juice and get an accurate reading of the PH.  Take your time to allow the meter to make its calculation, as it may take a bit of time to settle on the final number. Mine likes to stop and think about it for a minute or so, holding at one number, before it reads the final number.

PH is easy. TA not so much. It’s not that TA is complicated to discern, just a bit tricky in the lab technique. There are two methods of determining this number. The first is called the test tube method. It uses a colorant, phenolphthalein, and a titration chemical, sodium hydroxide (NaOH). It’s probably best if you purchase the chemicals as part of a test kit because the kit will include the instructions, the chemicals in their proper strength and a calculation table to translate the findings into TA levels. This acid test is not the test kit to determine whether a malolactic acid fermentation is complete. (Though you should have this test if you do this fermentation or if you suspect a natural onset of a malolactic fermentation, to avoid a wine that goes fizzy in the bottle).

The test tube method requires you exactly measure the added chemicals per instructions, including a measured amount of distilled water. It also requires you slowly add the titrant until the sample changes color, swirling the sample as you add the titrant. The amount of added sodium hydroxide at the change in color is listed on the companion chart and reveals the TA. The tricky part is going slow and mixing well between additions. Best practice to buy new chemicals every 6 months. The strength of the chemicals can fade, thus throwing off the calculation.

The second method also uses sodium hydroxide, but omits the colorant in favor of a PH meter. A measured sample of juice is also used with some added distilled water. Sodium hydroxide is slowly added to the test solution, swirling as you go, until the PH meter reads 8.2. A simple calculation yields the TA number. If you use .133 NaOH, then the calculation is even simpler at 2X the volume used.

Both of these methods require that the sample be continually mixed so as to even out the sodium hydroxide. The PH meter method also is tricky in that most of the volume of sodium hydroxide added is at the beginning of the test and somewhere below 7PH. After that PH level, mere drops of sodium hydroxide can race you past your target of PH 8.2 or your color change in the test tube method. So go slow! If using an ML syringe, switch over to a dropper after PH 7. There 20 drops in an ML.

Having repeatedly missed my mark, I invested in a burette, which is a tube that has a ballcock dropper and I can easily reduce the speed of the drops after PH 7. As it has a stand, I also don’t have to hold the dropper so I can concentrate on proper swirling of the sample.

In getting to these numbers, the three most important elements of doing a good job are having fresh chemicals, going slow, and if using a PH meter, making sure your meter is properly calculated. It’s crucial here.

Reaching Balance

So after you understand the basics of acid structure, having determined where you are with the acids, and then having decided where you want to go with the acids, how do you get to the Promised Land? There are ways to lower the acid level with the use of water, calcium carbonate or potassium carbonate or a combination of the three. This often occurs in cooler climate regions.

To raise acid levels, one can add tartaric acid, or acidified water. This deficit often occurs in warmer climate regions. In either situation, raising or lowering acid levels using water can affect sugar levels. Each has its own challenges.

Reducing Acid

Some winemakers recoil from the thought of adding water to the pre-fermentation must or juice to reduce the overall acid. But if you add small amounts, the effect on the overall taste of the finished wine is minimal. For vinifera, perhaps up to 5% of the overall volume can be added and with hybrids perhaps up to 10%. This has the benefit of reducing the acid profile while giving you a greater volume of wine. Also an added benefit is that it allows you to use fewer chemical additives. The downside of this, though, is a reduction in brix, which will need to be accounted for when chaptalizing.

I never add water after the fermentation is complete. It seems to have a much greater impact on the taste, even in small amounts.

Calcium carbonate is commonly used to reduce acid by neutralizing it. The package usually gives guidance on the amount to add and winebusiness.com has a web site to provide actual amounts for your batch. For me, calcium carbonate has a down side in that it take a very long time to clear and may leave a taste that lingers on the palate. Many people don’t agree on the residual taste. I would never use calcium carbonate after fermentation as it remain in the wine for a long time and may delay bottling. An upside is it does not affect the brix level.

Potassium carbonate is also used to reduce acid levels. It is fast acting, but needs a cold stabilization to have full effect. I don’t perceive any taste from adding it. This is my go-to carbonate, especially because you can add it pre and post-fermentation.

Potassium carbonate does affect the PH. So, if your juice requires a large correction, it may be wise to use calcium carbonate, or a combination of acid reduction techniques, to avoid a too high final PH level. Even possibly use a combination of carbonates (sequentially), or use some water to get the job done.

Increasing Acid

If you are working with warm climate grapes, you are more likely to have an opposite problem: Too little acid! But this problem is easily solved by adding tartaric acid. If white wine is being made, some malic acid might also be appropriate. Avoid citric acid as this can react with malic bacteria, giving it an unpleasant odor. Again, winebusiness.com can help with calculating the additions.

The tartaric acid can be mixed with water, which allows it to amalgamate more quickly in the must. Also, with warm climate grapes, the sugar levels can be elevated. The water will reduce the brix levels while the acid reduces the PH level.

How This All Works Together

Because wine cannot be trusted to follow the path suggested in any addition guide, I tend to make any additions (or reductions) very slowly and in three tranches. Additions sometimes just don’t correlate to what you would expect. Pre-fermentation, I use my target TA as the general guide, but I always check the PH and regardless of what the target is, I let the PH be the guide to when I stop. The pre-fermentation PH level should be a bit lower than your target PH.  The TA will get me to the neighborhood, but the PH tells me the proper address. Having left room for post fermentation correction, I have an additional buffer. I won’t have to re-acidify a wine I de-acidified, or vice versa.

Acid adjustment can occur before fermentation or after, but it makes more sense to make major adjustments before fermentation and polishing-final adjustments at the end of fermentation. PH generally rises in red fermentations, so a final PH needs to await the end of fermentation. I like to get my acid numbers in the “ball park” before I begin my fermentation. After fermentation, I can then taste the wine to determine if I need more acid reduction or increase after the wine finishes its fermentation, including after any malolactic fermentation. ML fermentation will also affect the PH, reducing the stronger malic acid to softer lactic acid. Also slightly affecting the acid balance is cold stabilization, again slightly lowering the PH levels. Get them all out of the way to see where you are at with the PH.

I don’t bother with TA after fermentation. I focus on PH, as that is what will determine how much sulfate you will need to add to keep the wine from oxidizing and thus spoiling. Also, I let my palate tell me whether the acid balance is correct. Other winemakers might want to continue to use TA as a guide to help them with measurements of carbonate or acid additions, even for minor adjustment. I feel that the TA number is ungainly in the post-fermentation polish.

TA can still be helpful where there are weird circumstances such as when the numbers are upside down, for instance where juice or wine has high acid andhigh PH. Normally acidic wines have a low PH. Some grape varietals can occasionally naturally have this problem, such as Gewürztraminer. Any attempt to overly reduce the acid will shoot up the PH to make the wine very unstable.

Sometimes purchased juice comes that way. I suspect (without any evidence) it may happen that some grape grower’s overuse of chemical fertilizer, containing elevated amounts of potassium which encourages fruit production, may cause high acid/high PH situations. An answer might be to forgo reduction and use sugar additions to mask the acid. 

The Promised Land

To make a good, balanced wine, a good winemaker needs to understand what acids are in the wine, how to measure them, and how to adjust them to create a good finished wine. But in the end, whatever the numbers say, the acid balance is for you to decide. Your palate is your guide. Your Promised Land is your glass.