Equipment

Caustic and acid cleaning

What do caustic and acid cleaners actually do, and how are they handled?

In short

The two chemistries do different jobs. Alkaline cleaning, usually based on sodium hydroxide with additives, saponifies fats and hydrolyses proteins so that organic soil lifts and disperses. Acid cleaning, usually phosphoric, nitric or citric, dissolves the mineral deposits that alkali will not touch.

A vessel cleaned only with alkali accumulates mineral scale; one cleaned only with acid accumulates organic film. Commercial regimes alternate, or use one and periodically the other.

Both concentrates injure people. Neither should be used without reading the supplier’s safety data sheet and using the protective equipment it specifies, and no figure published here or anywhere else substitutes for the concentration and contact time on the product’s own label.

What alkaline cleaning does

Sodium hydroxide raises the pH of the cleaning solution far enough to convert fats into soluble soaps and to break proteins into fragments that dissolve or disperse. In a cider house the organic soil is chiefly yeast, lees, pectic material and the film that grows on any wet surface, and alkali is what removes it.

Formulated cleaners add more than the alkali itself: sequestrants to stop hardness in the water precipitating, surfactants to wet the surface and carry soil away, and sometimes chlorine or peroxide as an oxidising booster. Formulated products are generally better than raw caustic for this reason, and their instructions are written for the job.

Hot alkali is far more effective than cold, which is why commercial clean-in-place regimes heat the caustic circuit. Heat also increases the hazard, and hot caustic splashing is a serious burn.

Alkali attacks aluminium, zinc, tin and galvanised surfaces vigorously, generating hydrogen in the process. It also damages wood, soft metals and some elastomers. It belongs on stainless steel and on materials the supplier says it belongs on.

What acid cleaning does

Acid removes what alkali leaves: calcium and potassium salts, tartrate deposits, water-hardness scale, and the mineral film that builds inside pipework. On stainless steel, a nitric or phosphoric acid clean also does something else useful — it removes surface iron contamination and helps re-establish the passive chromium oxide layer that makes stainless corrosion-resistant in the first place.

Acid is also used as a neutralising rinse after alkaline cleaning, which both removes caustic residue and leaves the surface in a slightly acidic state that is less hospitable to many organisms.

Citric and other organic acids are milder and are the usual choice at small scale, where the scale burden is lighter and the handling risk of a strong mineral acid is not worth taking.

Handling

These chemicals injure peopleSodium hydroxide causes severe burns and permanent eye damage, and it does so without the immediate pain that warns of an acid burn. Strong acids burn on contact and give off irritant fumes. Concentrates are always added to water, never water to concentrate, because the reaction is strongly exothermic and can boil and spit. Alkaline and acid solutions are never mixed with each other, and chlorine-containing products are never mixed with acid — that combination releases chlorine gas and has killed people in food premises. Every use requires the supplier’s safety data sheet, the protective equipment it specifies including eye protection, ventilation, and a plan for what to do if it goes wrong. Store them separately, labelled, away from food and away from anyone who does not know what they are.

Rinsing and residue

Both chemistries leave residue that must be rinsed out, and both leave residue that will damage the cider if it is not. Alkaline residue raises pH and tastes soapy; acid residue affects acidity and can strip a passivation layer if left too long. Rinse water quality matters too: rinsing a sanitised tank with untreated water reintroduces whatever the water carries.

A rinse is verified rather than assumed. At small scale that means rinsing until the rinse water runs clear and shows no soapiness or smell; commercially it means checking conductivity or pH of the final rinse against a defined value.

Disposal is the other end of the same question. Strong cleaning solutions cannot go into a soakaway, a watercourse or a septic system, and in most jurisdictions there are rules about what may go to drain. That is a matter for local regulation and the supplier’s guidance, and it is worth resolving before the first drum is bought rather than after.

Also answered on this page

Questions this page covers, so you can tell at a glance whether it is the one you want.

What is caustic used for in a cidery?
Do I need acid cleaner as well as caustic?
Can I use bleach to clean cider equipment?

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.

What should i know about stainless steel fermentation tanks — A stainless tank is a welded vessel, usually cylindrical, in an austenitic stainless grade chosen for corrosion resistance in acidic, chloride-containing conditions. It contributes nothing to the cider and lets no oxygen in.
Why does everyone say cleaning matters more than anything else — Cleaning removes soil — pomace, lees, tartrate, protein and the biofilm growing in it. Sanitising reduces the number of viable organisms on a surface that is already clean. They are two separate operations and the second does not work without the first.
How do i sterilise cider bottles — Wash them clean first, then sanitise with a no-rinse sanitiser or a sulphite solution, and fill while still wet with it. Bottles that look clean but have dried deposits inside are the usual source of bottle spoilage.
What sanitiser should be used on cider equipment
What is cork taint — Cork taint is a musty, damp-cardboard smell caused mainly by trichloroanisole, which can come from the cork or from the cellar. It strips aroma from the drink even below the level at which it can be identified.
What is cold stabilisation in cider

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.

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.
Hochschule Geisenheim University — beverage technology
Hochschule Geisenheim · university · retrieved 2026-08-24
German beverage-technology research covering apple wine and fruit juice processing, including the enzymology of clarification.
National Association of Cider Makers
NACM · specialist organisation · retrieved 2026-08-24
The UK trade association. Useful for industry-agreed definitions and for the voluntary labelling standards its members work to. A trade body has an interest in how its product is described, so CiderHQ cites it for what the industry says about itself rather than for neutral scientific claims.

Where to go next

Cider making equipment — The rest of the equipment material, grouped by what each piece is for.
How cider is made — The methods this equipment exists to carry out.
Troubleshooting — The faults that are traced back to equipment and to cleaning.