Juice treatment
Acid adjustment
Correcting the acidity of low-acid juice before fermentation, usually with malic acid, and the difference between the pH question and the titratable acidity question.
Also called Acidification, Malic acid addition, Juice acid correction.
- Stage
- Juice treatment
- Traditional in
- Normandy, Pays d’Auge, Herefordshire, Somerset
- What it most changes
- Acidity up, freshness up
- Safety
- None recorded
What it is
Some cider fruit is very low in acid. French and English bittersweet cultivars in particular can give juice with so little malic acid that the resulting pH sits high enough for spoilage organisms to be genuinely comfortable. Acid adjustment is the addition of acid — malic acid most commonly, since it is the acid the fruit itself carries, though citric and other permitted acids are used in some jurisdictions — to bring the juice down to a range where fermentation is microbiologically defensible and the finished cider has some structure. Blending with sharp fruit achieves the same end without an addition, and is often preferable.
Described in full
- Shape
- Two panels side by side, each representing a juice. Each panel contains eight small squares in two rows, standing for units of acid: the left panel has four filled and four drawn in dashed outline, the right has all eight filled. Beneath each is its titratable acidity — 4.0 and 8.0 grams per litre. A single wide band below both, with arrows leading into it from each panel, states that both read pH 3.6.
- What the squares count
- Acid groups available to a titration. The titration finds every one of them, dissociated or not, because the alkali drives the equilibrium until all of them have reacted. That is what titratable acidity measures: how much acid is present.
- What the meter finds
- Only the hydrogen ions actually free in solution at that moment. Malic acid is a weak acid, so most of it sits undissociated at cider pH, and the free fraction is a small part of the total.
- Buffering
- The juice also contains the potassium salts of its own acids, and those salts absorb added hydrogen ions. A juice rich in potassium therefore holds a higher pH than its acid content alone would predict, which is how two juices with very different acid loads arrive at the same meter reading.
- Why it matters
- Perceived sourness follows the amount of acid; microbial risk and sulphite effectiveness follow pH. A maker who measures only one of the two is blind to whichever question the other answers, and the two questions have different answers on the same juice.
Why it is used
- At high pH the antimicrobial activity of sulphur dioxide collapses, because the effective molecular form is a small and rapidly shrinking fraction of the total as pH rises, so a sulphite addition that would protect a sharp juice protects a bittersweet one hardly at all.
- Lactic acid bacteria, including the strains associated with ropiness and with acrolein formation from glycerol, are far more likely to establish in a high-pH cider than a low-pH one.
- A low-acid cider tastes flat and short regardless of its phenolic content, because acidity carries the finish and gives tannin something to work against.
- Correcting at the juice stage lets the fermentation and the malolactic conversion, if one occurs, happen at a pH the maker has chosen rather than one the season handed them.
How it works
- Malic acid is a dicarboxylic acid and the dominant acid of apple; adding it raises titratable acidity and lowers pH along a curve set by the juice’s buffering capacity, which is why the same addition moves different juices by different amounts.
- Potassium content is the main buffer. A juice from potassium-rich fruit resists pH change strongly, so a substantial acid addition may raise perceived sourness considerably while moving pH only modestly.
- pH governs the microbiology: it sets the molecular sulphur dioxide fraction, the activity of pectin methylesterase and other enzymes, and the growth thresholds of lactic acid bacteria. Titratable acidity governs the taste.
- If malolactic fermentation subsequently occurs, malic acid is decarboxylated to lactic acid, removing roughly half the acid function per molecule and raising pH, so an addition of malic acid is not necessarily permanent.
What it changes
The direction this step pushes the finished drink in, dimension by dimension. A direction, not a measurement: how far it moves depends on the juice, the temperature and how the step is carried out.
| Dimension | Direction | Why |
|---|---|---|
| Acidity | Raises | Additional dissociable carboxyl groups increase both the titratable acid and the free hydrogen ion concentration the palate registers as sourness. |
| Freshness | Raises | Acidity shortens and sharpens the finish and counteracts the soft, broad impression of a low-acid bittersweet juice, so the cider reads as livelier without any change in carbonation. |
| Astringency | Raises | Lower pH shifts phenolics towards forms that bind salivary protein more readily, so the same tannin load is perceived as drier and more gripping in a more acidic cider. |
The chemistry and the organisms
What is actually being changed, and by what. Each entry says what that compound or organism does in cider generally; this page is one place it does it.
Compounds involved
Malic acid
The acid of apples, which supplies almost all the sharpness a cider has and, through pH, decides how vulnerable that cider is to everything that could spoil it.
Citric acid
A minor acid in apples and a much more significant one in pears, whose metabolism by lactic bacteria is the reason perry gains more butter and more vinegar from malolactic fermentation than cider does.
Lactic acid
The softer acid that replaces malic when malolactic fermentation runs, halving the acid a cider carries and changing its texture as much as its sharpness.
Sulphur dioxide
The antimicrobial and antioxidant on which most modern cidermaking depends, and whose effectiveness collapses as pH rises — which makes every sulphiting decision a pH decision first.
Where it is traditional
The places this step belongs to as a matter of practice. It is not a claim of exclusivity — a method can be traditional in one region and perfectly ordinary in another.
What it is done with
Titration kits for total acidity
Total acidity is measured by titrating a measured sample with a standard alkali until all the acid is neutralised, and reading off how much alkali it took — a cheap, reliable measurement whose main pitfall in cider is finding the endpoint in a coloured liquid.
The pH meter and its calibration
A pH meter reads the activity of hydrogen ions through a glass electrode, giving the number that governs microbial safety and sulphur dioxide effectiveness — and it is worthless without regular calibration and proper probe storage.
What can go wrong
Faults that begin at this step, or that this step makes more likely. Each one is set out with its causes and whether it can be put right.
Low acidity
A cider without enough acid to give it definition, tasting soft, heavy and dull — and sitting at a pH that leaves it exposed to spoilage organisms.
Excessive acidity
Acidity high enough to dominate everything else, leaving a cider that is thin, hard and sour rather than fresh.
Ropiness
Cider that pours thick and pulls into an oily thread, caused by lactic acid bacteria secreting long-chain glucan polymers into the drink.
Microbial haze
Cloudiness caused by a growing population of spoilage organisms, and therefore a symptom of something worse rather than a clarity problem in itself.
Volatile acidity
The measurable fraction of acidity that can be steam-distilled off, dominated by acetic acid and read as vinegar sharpness in the nose and a hard, hot finish.
Mousiness
A retronasal taint of mouse cage, stale popcorn or crackers that appears only after swallowing — and that a substantial fraction of people cannot detect at all.
More on acid adjustment
The single most useful distinction in this subject is that pH and titratable acidity answer different questions, and it is the pH that determines whether a juice is microbiologically safe to work with. Titratable acidity tells you roughly how sour the cider will taste; pH tells you how much of a sulphite addition will exist in the antimicrobial molecular form, whether lactic acid bacteria will find the medium hospitable, and how stable the finished cider will be. The two move together, but not proportionally, because the juice’s potassium content buffers pH change. A maker who measures only titratable acidity can adjust a juice to a perfectly pleasant sourness and still be fermenting at a pH where sulphite is doing almost nothing.
This is not an abstract risk in bittersweet cider making. French cidre cultivars and the English bittersweets were selected for phenolic content and low acid, and blends composed entirely of them can sit at a pH high enough that ropiness, lactic off-flavours and acrolein bitterness become live possibilities rather than textbook curiosities. The traditional answer was never an acid addition — it was a blend. The Three Counties practice of building a blend from bittersweets with a proportion of sharps, and the Normandy classification that names acidulé fruit as a distinct category alongside doux and amer, both exist because the tradition understood that a blend needs an acid component. Where such fruit is unavailable, an addition does the same job less elegantly.
Regulatory positions differ and this is one of the places where a maker genuinely cannot generalise from one country to another. French cidre is defined by decree around a product made from apple or pear juice, with the permitted treatments enumerated, and the AOC specifications are tighter still than the general decree. United States federal rules are framed around what may be added to a wine or hard cider and under what labelling consequences, with acidification treated as a recognised cellar practice. UK rules approach cider through a juice-content definition with its own list of permitted operations. The practical instruction is to check the rules for the market the cider will be sold into, and to check them as they currently stand rather than as remembered.
What a practitioner decides, in order, is: measure pH, not just acidity; blend first if sharp fruit exists, because blending adds aroma and structure that an acid addition cannot; and only then consider an addition, made to the juice rather than the finished cider so that fermentation integrates it. The commonest error is over-correction, producing a cider that is aggressively sour and stays that way, since there is no gentle route back — deacidification is a clumsier operation than acidification and carries its own consequences for potassium and mouthfeel. The second commonest is forgetting that a subsequent malolactic conversion will undo part of the addition.
Related processes
Steps that sit alongside this one, replace it, or depend on it having been done.
Juice treatment
Juice blending
Combining juices from different cultivars before fermentation so that the blend ferments as a single batch, as against fermenting separately and blending later.
Blending
Acid balancing
Bringing a cider to the sharpness it needs, which requires separating perceived sharpness from titratable acidity from pH — three related things that do not move together.
Juice treatment
Sulphiting
Adding sulphur dioxide to juice to suppress spoilage organisms and oxidative browning, at a level that only means anything once the juice pH is known.
Fermentation
Malolactic fermentation
A bacterial conversion of sharp malic acid into softer lactic acid, which lowers acidity, changes aroma, and in most traditional cider happens whether it was planned or not.
Blending
Blending
Combining separate lots of cider or perry into one, which in cider is the historically normal way of making the drink rather than a remedy applied when single lots disappoint.
What people ask next
Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.
- How do i balance acid and tannin in a blend — Acid and tannin do different jobs and cannot substitute for each other: acid gives freshness and microbiological safety, tannin gives structure and length. A blend short of acid tastes flabby however tannic it is.
- How do you blend cider
- What is malolactic fermentation — Malolactic fermentation is a bacterial conversion of sharp malic acid into softer lactic acid, releasing carbon dioxide. It lowers total acidity and raises pH, and in cider it is often the source of a farmyard or buttery note as well.
- Why is sulphite added to cider — Sulphur dioxide suppresses spoilage bacteria and wild yeast before fermentation and protects the finished cider from oxidation. How much of it is active depends strongly on pH, which is why low-acid juice is harder to protect.
- Does cider contain sulphites — Most does. Sulphur dioxide is added to protect juice and finished cider, and fermentation itself produces a small amount even when none is added. European labels must declare it above 10 mg per litre.
- What is malic acid and why does it matter in cider — Malic acid is the acid of apples and supplies almost all the sharpness a cider has. It also sets pH, which decides how well sulphite works and how exposed the cider is to spoilage, so it does far more work than its taste suggests.
Where to go next
- How cider is made — The whole sequence, stage by stage, with the choices open at each one.
- Cider science — The chemistry and microbiology the methods on this page rest on.
- Troubleshooting — What goes wrong, how to recognise it, and whether it can be reversed.
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
The Science of Cidermaking and associated technical writing
Andrew Lea · reference work · passage verified 2026-08-24
Written by a food chemist who worked at Long Ashton on apple phenolics. Unusual among specialist cider writing in that it is primary-research-adjacent: the author is describing work he did, and cites the literature. This is why it is registered at tier 1 for chemistry while a general cider book is not.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
Légifrance, JORF texte n° JORFTEXT000051223792 · legislation · retrieved 2026-08-24 · covers In force from 1 July 2025; “artisanal” and “rosé” from 1 January 2026
Opened on 2026-08-24, and it turned out that the entry CiderHQ had was describing a repealed instrument. The décret of 20 February 2025 replaces the 1953 décret and the 1987 one that amended it, and it changes the thing this site had been repeating: the doux, demi-sec and brut categories are no longer residual-sugar bands. They are now defined on acquired alcoholic strength together with density at 20 °C, an extra-brut tier has been added, and the four bands deliberately overlap so that a producer can place a product with a hydrometer rather than a sugar analysis. The pages that said otherwise have been corrected. What could not be done is a verbatim read: legifrance.gouv.fr returns HTTP 403 to retrieval, so the text was read through a summarising fetch and every operative figure was then checked independently against the UNICID interbranch briefing, which reproduces the table. The two agree.