Editor’s Note: For convenience, we’ve created a collection of all current cider articles by this author.

By Michael Wilcox

Acidity is sensed in the mouth as sourness or tartness. Some acids have an aroma but most of the “good” or desirable cider acids have little to none. Acidity is a vital component of cider and perry, and a range of it can give a fresh taste, provide preservation from infection, or give a harshness that makes the beverage undrinkable. Its effect on mouthfeel can be to cut through the viscosity provided by residual sweetness. This can be a positive with an extremely sweet ice cider, or occasionally make a cider seem too thin. High sourness can feel like it is taking enamel off your teeth while a lack of acidity can leave a cider flabby, boring, and prone to microbial contamination. Cider with high acidity will generally age better than that with low, but other components like tannins and alcohol also play a role.

Since cider and perry are literally wines made with apples or pears, we’ll briefly compare grape acidity with that of apples and pears before talking about acidity in finished cider and perry.

Acids in the Fruit

The main acid found in apples is Malic Acid . Though present in most fruits, it can represent more than 95% of acidity in apples. The flavor and character of this acid is thus strongly associated with Apples. Pear acidity is also composed of a large portion of malic acid, but also may contain a significant portion and occasionally even a majority of Citric Acid . Pears may also contain low but discernible amounts of acetic acid. Tartaric Acid is mostly associated with grapes, though it is also present in other fruits like cranberries and prickly pears. Though unripe grapes can have as high as a 3:1 malic/tartaric ratio, malic acid is reduced significantly during the ripening process, so by the time fermentation begins, acidity is largely tartaric. This reduction is very dependent on climate, particularly nighttime temperatures. For example, cool-climate grapes may be more malic and thus more acidic.

Malic acid

This acid has a sharp, strong taste of green apples or rhubarb (another plant with high amounts of malic). Unlike tartaric acid it is widespread in nature. It can be harsh and metallic at high levels. Unripe fruits tend to be full of malic acid – that which can provide freshness in a moderate amount is unpleasant at high level when the fruit is green/unripe. It is diprotic (we’ll get to this in a little bit…) and can be converted into the softer lactic acid through malolactic fermentation (MLF).

Tartaric acid

Predominant only in grapes. It is also diprotic and is a stronger acid than malic. I find the flavor more pleasant than malic, like a salty soft lime, but as a fairly strong acid, it is highly mouth-watering. (Relatively speaking, at least – tartaric is a fairly weak acid, but is still 2-3 times as strong as malic.) Tartaric is a target of significantly fewer microbes than malic or citric, tending to make it more stable than the other two. This makes it a good choice for post-ferment adjustments, however there are limits to its use. Unlike malic acid, tartaric has a fairly low solubility limit, especially when chilled – you may have seen crystals of it in in wine bottles. These crystals or “wine diamonds” are formed of potassium bitartrate. (That Cream of Tartar you shove out of the way in your spice cabinet? – same stuff.)

Citric Acid

Commonly associated with citrus where it is the predominant form of acidity, this acid is also found in significant amounts in berries and many other fruits. This acid is weaker than the other two and odorless with a fairly-distinctive tangy/sour flavor, associated more with a “freshness” character than malic/tartaric. It is tends to be easily converted during fermentation – by yeast into lactic acid, and by lactic acid bacteria (LAB) to acetic acid.

Ascorbic Acid, or Vitamin C

Not to be confused with Citric Acid, Ascorbic is often found in commercial apple juice. Though theoretically a truckload of the very weakly acidic Vitamin C could lower pH enough to promote microbial stability, the usual use of Ascorbic is as an antioxidant, generally for color stability (Ascorbic is an even weaker acid than acetic). Ascorbic tastes quite bitter compared to the sour Citric Acid flavor. Other than being already present in commercial apple juice, you’re more likely to encounter Ascorbic Acid in a mead or wine kit.

Acids in finished Cider and Perry

Malic acid is almost always present. Tartaric should be noticeable only in finished (grape) wine. Citric acid tends to be consumed during fermentation but may be present in the finished product, especially with fruits other than apples. Also, citric is a component of “Acid Blend” along with tartaric and malic and could have been used to adjust the cider. (Side Note: do you know the blend % of your particular brand of Acid Blend? You really should…)

Carbonic acid – Cutting through sugar, carbonation helps make many ciders and perries great for food. This acid is very weak, but as you know from beer, it can increase acidity slightly.

Lactic Acid – Commonly associated with dairy products like yogurt, this acid is fairly light and refreshing. The fairly soft mouthfeel of lactic acid is in contrast to the much “harder” sometimes metallic malic acid. It is a weak acid and monoprotic. LAB make lactic acid (and CO2) from malic acid. Both yeast and LAB can also make lactic acid from sugar during primary fermentation.

Acetic Acid – Everyone knows this one – the distinctive smell and flavor of vinegar. You may notice a harshness in the swallow, a “burn” in the back of the throat/aftertaste. Acetic Acid is pretty much always present in cider, and at very low levels is a positive flavor contributor. The thing is as soon as you can taste it, it is generally a fault. As pears may contain small amounts of this acid right off of the tree, a low but noticeable amount of acetic acid is NOT considered a fault in Perry. Note that Acetic Acid is part of Volatile Acidity (VA), the other notable component of VA being Acetone (nail polish remover).

“So what’s this mono/diprotic stuff?”

Most judges are familiar with pH, basically the concentration of hydrogen ions (i.e. protons) in a solution. It is a negative logarithmic scale, thus the lower the number the more acidic the solution. As a logarithmic scale, pH of 2 is 10x as acidic as pH of 3, which is 10x as acidic as pH of 4, and so on. For the record, a pH of 2 is extremely sour, approximating that of lemon juice, while 3 is fairly common in a tart cider, and 4 is really getting too high to be a microbially stable cider.

Recall that apple acidity is almost entirely malic. Malic acid is diprotic, while lactic is monoprotic, and in the simplest terms this means malic acid releases twice as many protons into the solution. Replacing malic acid with lactic (through MLF) thus means a reduction of the protons in solution, a decrease in acidity and a corresponding increase in pH.

If you really hate chemistry, skip to the next section for practical judging tips related to acidity in cider and perry.

[Note for the experts here: Yes, I’m really oversimplifying things, and mostly omitting talk of Total or Titratable Acidity measurements. Taking off my Judge pin, one is looking at amount/strength of acidity for stability purposes, and the other at how acidic it tastes. Yes, two beverages could have the same pH but differ significantly in TA. With plain cider we’re dealing almost exclusively with Malic. Get into other beverages, and other fruits, and it becomes more confusing. Even TA is generally given as the dominant acid in a particular fruit, i.e. will vary if given as g/L tartaric, malic, or citric. I’m keeping it simple because I view these things are more important for a cider MAKER, and less important for a cider JUDGE. A judge only knows how it tastes and feels on their palate. So I choose to use the pH term that more people are used to.]

Suffice to say the comparative ease or difficulty with which various substances give up their first, second, or third protons, or whether MLF is actually an enzymatic decarboxylation rather than true fermentation, are beyond the scope of judging. Any BJCP chemists are welcome to argue this stuff amongst themselves. The point is the acidity goes down. With grape wine a drop in acidity of 1-3 g/L and corresponding pH increase of 0.1 – 0.3 units is expected during MLF, but as apples are almost entirely malic, this change can be significantly greater in a cider – converting all the malic to lactic would basically reduce acidity by half.

Recall that pears contain significant citric acid, and that LAB can turn that into acetic acid. This is generally why MLF is avoided with Perry – pears and their fermented counterpart tend to be fairly delicately flavored, and there isn’t a lot of room to hide much vinegar before it becomes a fault. Also, as pears tend to be a little less acidic than apples, some perries cannot handle as much increase in pH before losing microbial stability.

MLF does more than just reduce acidity, but we’re going to talk about the various organisms that might be performing MLF, under what conditions they like to work, and what their various effects are, in a later article.

I hate chemistry; what does this stuff mean for me as a judge?

If you want to judge cider, you should be tasting cider before you start. If you find everything is too tart, perhaps these categories are not for you. But, simply given the frequency of sour beer fans among the BJCP, I doubt it will be much of an issue.

C1A New World Cider tends to be quite acidic, a function of using moderate to highly acidic apples. MLF is rare in this style and if it did undergo MLF, there is no taste or aroma component thereof. No noticeable vinegar.

Acidic apples are also used in C2A New England Cider thus this style should not have low acidity either. If sweetness is not particularly elevated, moderate acidity can work here, especially with some noticeable alcohol.

C2C Applewine often uses sharp apples, though it gets more of its structure from alcohol than New World. Applewine acidity is generally at least moderate, but a very high alcohol and acid combination will often come across as harsh. The style is referred to as the most like white wine – recall that with their lower tannin levels, white wine acidity is often higher than that of red wine.

C2D Ice Cider will likely be the most acidic thing in your flight, at least by measurement. However, depending on the alcohol and especially residual sugar level, it may come across to your palate as anywhere from screamingly tart to cloyingly sweet. You’re looking for something in the middle, a harmony of acid and sugar, acidity cutting through full body and lingering richness and flavor without harshness. Ice cider would be sipped slower, as compared to most of the other styles we have, but it needs to be fairly drinkable. The best are generally called “dangerous.”

C1B English and C2C French ciders get more of their structure from tannin, thus in general acid levels are lower than New World. There should be no noticeable vinegar. Super high acid would clash with high tannins, and these beverages need to be drinkable.

C2D/E Perry can be refreshingly tart or moderately low in acid if there are other elements of structure. Don’t knock the entrant for a slight vinegar character, which is acceptable.

Acetic acid is also a component of many Spanish Ciders, but we don’t have guidelines for that yet, and it’s not the only component – your unintentional apple cider vinegar isn’t going to do well here.

**Next time I’ll talk about the other components of cider: Sweetness/fruitiness, tannin, and alcohol, and their interplay with the acids we just discussed.**