The Point of Acids in Wine
Acids are in wine to give them the crisp, tart taste they are known for. This are a number of things that moderate acids and give your wine balance. These include sugar, alcohol, minerals, and other ingredients. Some of the acids come from ingredients you put in the wine while others are natural byproducts of fermentation.
The natural acids you get from your ingredients have the freshest, purest tastes. Acids you get from fermentation have milder, more complex taste. Natural acids common in grapes are tartaric, malic, and citric. Oxalic acid is another common natural acid. It's found in rhubarb and other ingredients. Fermentation acids include lactic, succinic, and acetic.
Since acidity has such a major influence on the taste of you wine, you need to make sure you understand the roles of various acids. You need to know their occurrence in common bases for making wines, their tastes, their sufficiency, how to measure them, and the principles for adjusting them when necessary.
Various Acids and Their Roles
The major grape acids are tartaric and malic. Citric is considered a minor acid, but is quite common. When you don't have enough naturally occurring acid in your base, it's common to add a blend of tartaric, malice, and citric acid. Sometimes you'll find that only adding one acid - most often citric - makes the best tasting wine. Understanding the roles of both major and minor acids in wines is critical, even if the only reason is knowing why their control is critical beyond the obvious role of taste.
Acids help yeast do what they need to do. It's certainly true that yeast will reproduce and convert sugar into CO2 and alcohol without any acid present, it does help. Even without being required by yeast, acids play other even more important roles. Taste is an obvious role. But what acid does that most people don't think about is stop or retard the growth of money potentially harmful microorganisms that would spoil your wine.
Tartaric acid is the most important acid you'll get to know. It's found in basically no other fruit other than grapes and it's the predominate acid in most wines. It's the strongest and most voluminous acid in grape wines and, since it has potassium and calcium salts, basically controls the acidity (pH) of wines. This contributes to a wine's color, aseptic stability (the resistance to bacterial infections), and taste. Therefore, a wine with a tartaric acid deficiency can have a lot of problems.
Most non-grape wines are made with either raisins or grape juice as a minor ingredient to add vinous qualities to the wine, most notably body and mouth-feel. So even when a wine's major component has no grapes, tartaric acid becomes an important component of the wine. The hardness in taste that tartaric acid is noted for can conflict with the softer acids normally found in non-grape wine bases.
Malic acid, on the other hand, is found in almost all of the fruits and vegetables that wines are made with. The amount of malic acid in fruit is affected by the climate the fruit is grown in. Warmer climates produce less malic acid in ripe fruit. No matter where the fruit is grown, there is less malic acid in ripe fruit than unripe fruit. When there is an excess of malic acid there tends to be a sharply greenish taste. Reducing the amount of malic acid is often a major considerationin toning down or smoothing out your wine. Fermentation is a great way to accomplish this, as 20-30% of the harvested malic acid is respired during fermentation. If your fermented wine still has too much malic acid, a malolactic fermentation can be encouraged where malic acid is converted to weaker lactic acid. Normal fermenation produces some lactic acid (the same stuff that makes your muscles sore after working out), but malolactic fermentation (MLF) can reduce malic and increase lactic fivefold.
Lactic acid is much milder in taste than malic acid, but it's also a two-edged sword. It's mildly sour taste counteracts the harsher tartness of malic acid very well. But it can also invite infection by some lactic bacteria that can produce odors suggestive of spoiled milk or sauerkraut. Because of this a number of winemakers will say you should never use MLF, while a number will also say it's a great idea. Another reason for dissuading MLF is that certain wines require it to attain their noted tastes.
Citric acid is minor in grapes but a major component of many other fruits. It's normally added to wines to increase acidity, prevent ferric hazes, or complement a specific flavor. Just like malic acid reduces during fermentation, any citric acid found in grapes will basically disappear. If you add it to an almost finished wine to increase acidity, citric acid will give the wine a freshness of flavor that seems - and is - artificial.
Acetic acid is a very volatile and odorous acid. It's detectable as the small of vinegar. Most wines have it naturally in very small quantities. It's formed very quickly by certain bacteria being exposed to air. The only reason it's in wine is to spoil it.
Succinic acid is a byproduct of yeast fermentation and is found in trace amounts in all wines. It's taste is a mixture of acid, salt, and bitterness. It is also considered to be the best acid for producing rich, flavorful esters during aging.
Other commonly found acids that are found in trace amounts and contribute to total acidity include: citramilic, dimethylglyceric, galacturonic, gluonic, ketoglutaric, mucic, oxalic, and pyruvic.
The Dominant Acids in Common Wine Fruits
| Base | Acid |
|---|---|
| Apple | Malic |
| Apricot | Malic |
| Banana | Malic/Citric |
| Bilberry | Citric |
| Blackberry | Malic |
| Blueberry | Citric |
| Boysenberry | Malic |
| Cherry | Malic |
| Choke Cherry | Malic |
| Crabapple | Malic |
| Cranberry | Citric/Malic |
| Currant, Black | Citric |
| Currant, Red | Citric |
| Currant, White | Citric |
| Dewberry | Malic |
| Elderberry | Citric |
| Fig | Malic |
| Gooseberry | Citric |
| Grape | Tartaric/Malic |
| Grapefruit | Citric |
| Huckleberry | Citric |
| Kiwi | Citric |
| Kumquat | Citric |
| Lemon | Citric |
| Lime | Citric |
| Loganberry | Malic/Citric |
| Marionberry | Malic |
| Nectarine | Malic |
| Orange | Citric |
| Passion Fruit | Malic |
| Peach | Malic |
| Pear | Malic |
| Plum | Malic |
| Pomegranate | Citric/Malic |
| Raspberry | Citric |
| Rhubarb | Malic/Oxalic |
| Rosehip | Malic |
| Salal | Citric/Malic |
| Salmon Berry | Malic |
| Saskatoon Berry | Malic |
| Strawberry | Citric |
| Tangerine | Citric |
The Tastes of Various Acids
Emile Peynaud, in his book Knowing and Making Wine, suggests the following experiment intended to help familiarize you with the different tastes of acids.
Prepare the following six buffered solutions with the same pH:
- Tartaric acid a 1 g/L
- Malic acid at 1 g/L
- Citric acid at 1 g/L
- Lactic acid at 1 g/L
- Acetic acid at 1 g/L
- Succinic acid at 0.5 g/L
Taste each of the solutions in turn, clearing the palate between each tasting. The acids will never be this intense in a real wine, but it's the best way to help you in your future decisions about acidity in your wines.
Doing this experiment you'll realize that tartaric acid produces the hardest taste, malic acid the most pronounced, citric acid the freshest, lactic acid the weakest, acetic acid the most bitter and odorous, and succinct the saltiest. Using this knowledge you might make these decisions:
- Cold stabilization to reduce tartaric acid
- MLF to convert harsher malic acid into tamer lactic
- Adding citric acid to a malic dominant fruit base
- Adding tartaric acid to a weak, citric dominant fruit base
- Adding a blend of acids to round-out acidity in a weak base
When you make these decisions it's important to record them in a wine log so you can refer back to them when trying new recipes. That's the only way to make sure that you're making the correct judgements. When you make a wine that's really good or really bad you can refer back to your log to figure out exactly why.
How To Tell If You Have Enough Acid
Assuming you can measure the acidity of your wine, how are you supposed to know if the total acid is correct? This can be subjective, since you may like your wine more or less acidic. When you get the combination of acids, tannins, alcohol, and sweetness right, even very acidic wines will seem less acidic than they are.
There are some normal guidelines you can use for ballpark estimates of what may be acceptable levels. They are just guidelines, and won't be perfect for every situation.
The numbers in the table below reflect the total titratable acids (TA) as an expression of percentage of weight. 0.65% equals 6.5 g/L or 0.65 g/100mL.
| Type of Wine | Acidity % |
|---|---|
| Dry White Grape Wines | 0.65-0.75% |
| Sweet White Grape Wines | 0.70-0.85% |
| Dry Red Grape Wines | 0.60-0.70% |
| Sweet Red Grape Wines | 0.65-0.80% |
| Sherry Grape Wines | 0.50-0.60% |
| Non-Grape White Wines | 0.55-0.65% |
| Non-Grape Red Wines | 0.50-0.60% |
If your wine is well balanced you can exceed these guidelines and find that the wine is still quite palatable. If your wine comes in below these guidelines though, your wine may actually seem too acidic to enjoy. One thing you'll learn is there are very few absolutes in wine making.
Testing the Acidity
There are a wide range of inexpensive acidity test kits you can find at your local homebrew or winemaking supply store for under $10. You can also find them on Amazon. The pH test is simple, effective, and lets you know what's going on in your wine.
- In most kits you just add a 15 cc sample of your wine to a clear sample bottle or glass
- Then you add to your sample drops of phenolphthalein, a pH indicator
- Then you fill a syringe with a titrate solution, most commonly sodium hydroxide
- You then add the titrate solution .5 cc at a time to the sample and shake or stir it
- The color will change - pink for white wines, gray for red wines. The amount of titrate solution used is the key to the titratable acidity of the wine. Every cc of solution added equals 0.1% TA. So if you used 5.5 cc of solution to produce the indicated color, the TA of the wine would be 0.55%.
The Keys to Increasing and Decreasing Acidity
There are a number of ways you can increase acidity in musts. If you follow most of the recipes you find online, the recipe will likely attempt to take acid deficiencies into account by having you add a quantity of a specific acid, a blend of tartaric, malic and citric acids (called acid blend), or the juice of a citrus fruit (normally lemon or orange).
Keep in mind recipes are using base ingredients that may differ in natural sugar content or acidity from the same base ingredients you might get. So if your recipe tells you to add a teaspoon of acid blend to get the corrected acidity right, that's for the ingredients the recipe author had at hand. A teaspoon may or may not be correct for your base.
There are a number of reasons acidity varies, but the common reasons are differences in varieties, differences in the soil, the amount of water available during plant growth, differences in the temperatures during growing, differences in the sunlight, and even differences in the maturity in the fruit when it was harvested.
Therefore if you really want balanced wine you'll measure the acidity and correct accordingly, not just according to what the recipe calls for.
Acid blend is commonly used to increase the acidity of your must. There are several difference formulations of these blends. Commercial acid blends normally contain tartaric, malic, and citric acids in one of these ratios: 40-40-20; 40-30-30; 50-30-20; or 50-25-25. If you're looking for precision - and you should be - be sure to ask your supplier what their specific ratio is. The most common blends are 40-40-20 and adding 3.9 grams of this ratio to a gallon of must will increase the acidity approximately 0.1%. If you add 3.78 grams of pure tartaric acid you will get the same increase.
Sometimes recipes will use Fumaric acid in food grade powder form since it tends to inhibit malo-lactic fermentation when used between 1.5 to 5.7 grams per gallon. This gives you an increase of 0.05 to 0.15% acidity. When you use large doses of fumaric acid it may affect the flavor, so it's best to test it in a sample of wine before using it.
Fermentation will lose almost all citric acid you add, which is why it's best to add it after all signs of fermentation of ceased.
Malic acid can be added at any point in the process, but it also has a potential disadvantage. Malic acid buffers to a fairly high pH, so if your goal is to increase acidity and/or lower the pH you shouldn't use it. To lower pH you will want to use tartaric acid.
If your finished win is too acidic, you can easily fix that by adding calcium carbonate, acidex, or potassium bicarbonate. You can also use cold stabilization.
Calcium carbonate reacts best with tartaric rather than malic acid, so you shouldn't try to reduce acidity more than than 0.3% through it's use. Using 2.5 grams per gallon of wine lowers TA about 0.1%. After using calcium carbonate you should bulk age the wine at least 6 months to allow calcium malate, a natural byproduct, to precipitate from the wine. You should then cold stabilize the wine to ensure tartrate crystals do not precipitate out after bottling.
Potassium bicarbonate is used to deacidify a wine with a low pH (under 3.5), but it shouldn't be used to reduce acidity more than 0.3%. Using a dose of 3.4 grams per gallon of wine lowers the acidity by about 0.1%. After it's use, your wine should be cold stabilized as up to 30% of the potential acid reduction occurs then. You will get a greater rise in pH than calcium carbonate for an equivalent reduction in acidity.
Lastly, potassium bitartrate (aka cream of tartar) is used to help promote cold stabilization. It promotes the formation os tartrate crystals and is used at 2-5 grams per gallon. You then need to rigorously stir. If you use it you'll get better and quicker stabilization. You'll also get the benefits at a slightly higher temperature than if you don't use it.
pH - Another Way to Measure Acidity
There are two ways to measure acidity - titratable acidity (TA) and the potential of hydrogen (pH). Titratable acidity was discussed above. pH is related to an acid's strength in solution and is measured on a logarithmic scale. On the pH scale 7 is neutral. Numbers above 7 are alkalize and increase as the number gets higher. Numbers below 7 are acid and increase as the number lowers.
A pH of 9 is more alkaline (or basic) than a pH of 8, but a pH of 4 is more acidic than a pH of 5. Because pH uses a logarithmic scale, a pH of 4 is ten times more acidic than a pH of 5.
Although TA and pH are interrelated, they are not the same thing. A solution containing a specific quantity of a weaker acid such as malice with have a higher pH than a solution containing the same quantity of a stronger acid like tartaric.
For more on pH check out wikipedia.
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