Airlocks
This page covers the essentials. Additional sections — cold crash suck-back detail, retirement criteria, and the grommet/stem interface — are in preparation.
An airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. is a one-way valve fitted to the fermenter lid. It allows CO₂ produced during fermentation to escape while preventing air, wild yeast, and bacteria from entering the fermenter. It is one of the simplest components in the setup and one of the most important.
Types
Two designs are in common use. Both work.
3-piece airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. — a cylindrical body with a removable cap and an inner float. The float rises on CO₂ pressure and lets gas escape around the rim, then drops back to seal when pressure equalises. Easy to disassemble and clean thoroughly. Recommended.
S-type (double-bubble) airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. — a single moulded S-curve body. Gas bubbles through the liquid fill in both chambers. Cannot be fully disassembled — cleaning is limited to flushing. Adequate for most use but the 3-piece is easier to maintain.
Materials
AirlocksAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. are typically made from PPPP — Polypropylene A semi-crystalline polyolefin plastic widely used in fermenter buckets, lids, taps, and airlocks. Excellent chemical resistance across all homebrewing chemical environments. EU Regulation 10/2011 compliant. or SANSAN — Styrene-Acrylonitrile copolymer A transparent plastic used in some airlocks and equipment. The acrylonitrile content gives better chemical resistance than GPPS, particularly against DDBSA in acid-based sanitisers. Rated A for ABNS, unlike GPPS which is rated B/D. (styrene-acrylonitrile). Both are A-rated for all brewing chemicals at ambient temperature.
Some airlocksAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. — particularly compact designs — may be made from GPPSGPPS — General-Purpose Polystyrene The standard grade of polystyrene — amorphous, rigid, transparent, and inexpensive. Carries RIC code 6. Susceptible to DDBSA-driven environmental stress cracking (ESC) under WDC conditions — rated B at working dilution, D under accumulated WDC. Confirmed in Enolandia compact airlock (cod. 14037/14038) and cylindrical fermenter with float (cod. 11965) by Declaration of Conformity. (general-purpose polystyrene). GPPSGPPS — General-Purpose Polystyrene The standard grade of polystyrene — amorphous, rigid, transparent, and inexpensive. Carries RIC code 6. Susceptible to DDBSA-driven environmental stress cracking (ESC) under WDC conditions — rated B at working dilution, D under accumulated WDC. Confirmed in Enolandia compact airlock (cod. 14037/14038) and cylindrical fermenter with float (cod. 11965) by Declaration of Conformity. is chemically weaker than SANSAN — Styrene-Acrylonitrile copolymer A transparent plastic used in some airlocks and equipment. The acrylonitrile content gives better chemical resistance than GPPS, particularly against DDBSA in acid-based sanitisers. Rated A for ABNS, unlike GPPS which is rated B/D. and should not be soaked in concentrated ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution. or alkaline cleaners for extended periods. If the material of your airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. is not stated, treat it as GPPSGPPS — General-Purpose Polystyrene The standard grade of polystyrene — amorphous, rigid, transparent, and inexpensive. Carries RIC code 6. Susceptible to DDBSA-driven environmental stress cracking (ESC) under WDC conditions — rated B at working dilution, D under accumulated WDC. Confirmed in Enolandia compact airlock (cod. 14037/14038) and cylindrical fermenter with float (cod. 11965) by Declaration of Conformity. and limit soak time to 30 minutes maximum. See the PS/SAN materials page for the full compatibility analysis.
SANSAN — Styrene-Acrylonitrile copolymer A transparent plastic used in some airlocks and equipment. The acrylonitrile content gives better chemical resistance than GPPS, particularly against DDBSA in acid-based sanitisers. Rated A for ABNS, unlike GPPS which is rated B/D. is typically crystal-clear with a faint blue tint. GPPSGPPS — General-Purpose Polystyrene The standard grade of polystyrene — amorphous, rigid, transparent, and inexpensive. Carries RIC code 6. Susceptible to DDBSA-driven environmental stress cracking (ESC) under WDC conditions — rated B at working dilution, D under accumulated WDC. Confirmed in Enolandia compact airlock (cod. 14037/14038) and cylindrical fermenter with float (cod. 11965) by Declaration of Conformity. is clear but more brittle and has a slightly duller appearance. When in doubt, treat as GPPSGPPS — General-Purpose Polystyrene The standard grade of polystyrene — amorphous, rigid, transparent, and inexpensive. Carries RIC code 6. Susceptible to DDBSA-driven environmental stress cracking (ESC) under WDC conditions — rated B at working dilution, D under accumulated WDC. Confirmed in Enolandia compact airlock (cod. 14037/14038) and cylindrical fermenter with float (cod. 11965) by Declaration of Conformity..
Fill liquid
The liquid in the airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. U-section creates the seal. The choice of fill liquid matters.
Working-dilution ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution. (StarSan, StellarSan) — the recommended fill liquid. Already sanitised, compatible with all airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. materials, and harmless if suck-back occurs during cold crashing. Use the same solution you mixed for brew day sanitisation.
Cooled boiledBoiling Heating wort to a rolling boil (typically 60–90 minutes) to sterilise it, drive off unwanted compounds (including DMS precursors), concentrate sugars, and isomerise hop alpha acids into bitterness. Boiling is a hot-side process — it does not occur in Brew 1, which uses a pre-boiled kit. water — acceptable if no ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution. is available. Plain tap water carries a small contamination risk if suck-back occurs; boiledBoiling Heating wort to a rolling boil (typically 60–90 minutes) to sterilise it, drive off unwanted compounds (including DMS precursors), concentrate sugars, and isomerise hop alpha acids into bitterness. Boiling is a hot-side process — it does not occur in Brew 1, which uses a pre-boiled kit. and cooled water eliminates this.
Do not use undiluted DESDES — Disinfectant Ethanol Sanitiser ChemiPro DES. An ethanol-based (70–80%) sanitiser with no non-volatile residue. Evaporates completely, leaving no WDC risk. A-rated for all common homebrewing materials. (ethanol) — at 70–80% concentration, suck-back delivers a slug of alcohol directly into the fermenter headspace, which can damage or kill yeast at the liquid surface. DESDES — Disinfectant Ethanol Sanitiser ChemiPro DES. An ethanol-based (70–80%) sanitiser with no non-volatile residue. Evaporates completely, leaving no WDC risk. A-rated for all common homebrewing materials. is not suitable as an airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. fill liquid.
Do not use plain tap water — contamination risk from suck-back is low but non-zero. Cooled boiledBoiling Heating wort to a rolling boil (typically 60–90 minutes) to sterilise it, drive off unwanted compounds (including DMS precursors), concentrate sugars, and isomerise hop alpha acids into bitterness. Boiling is a hot-side process — it does not occur in Brew 1, which uses a pre-boiled kit. water or ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution. is the better choice.
Fill to the indicated level on the airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. — typically the line marked on the body. Overfilling increases suck-back volume if negative pressure develops; underfilling reduces the seal.
Installation
- Sanitise the airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. by submerging in working-dilution ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution. for 30 seconds. Do not rinse.
- Fill to the indicated level with fresh working-dilution ABNSABNS — Acid-Based No-Rinse Sanitiser The class of acid-based sanitisers used in homebrewing, combining phosphoric acid with an anionic alkylbenzenesulfonate surfactant. The acid creates a low-pH environment hostile to microorganisms; the surfactant disrupts cell membranes. Examples: Star San, Sanipro Rinse, StellarSan, Chemsan. Approved for use on food-contact surfaces without rinsing when used at the manufacturer's specified dilution..
- Fit the airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. stem into the grommet in the fermenter lid. It should seat firmly with light hand pressure — push until resistance is felt, not until the grommet deforms.
- Do not overtighten or force. The seal is made by the grommet compression against the stem, not by driving the airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. deep into the lid.
Reading the airlock
Bubbling indicates CO₂ is escaping — fermentation is active, or the fermenter is still off-gassing after active fermentation has slowed.
No bubbling does not mean fermentation is complete. Common causes include: fermentation genuinely finished; temperature drop reducing CO₂ solubility and gas production; a small leak in the lid seal allowing CO₂ to escape another way. The only reliable way to confirm fermentation is complete is to measure gravity on two consecutive days and confirm it is stable. The airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. is a useful indicator, not a definitive one.
Cleaning
3-piece airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use.: disassemble completely after every brew. Soak all parts in warm alkaline cleaner (PBWPBW — Powdered Brewery Wash A sodium metasilicate and percarbonate-based alkaline cleaner widely used in brewing. Removes organic soil through alkaline hydrolysis. A-rated for all common homebrewing plastic and elastomer materials at working concentrations. or StellarClean) for 15 minutes. Rinse thoroughly. Inspect the float for residue in the joint around the rim.
S-type airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use.: flush thoroughly with warm water immediately after use while residue is still wet. Soak assembled in alkaline cleaner and flush again. Full disassembly is not possible — if residue persists, replace rather than brew with a suspect airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use.. AirlocksAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. are inexpensive.
Retirement
Replace an airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. if:
- The body is cracked or cloudy in a way that obscures the fill level
- The float (3-piece) no longer seats correctly or shows visible residue that cleaning cannot remove
- The stem is damaged or deformed in a way that compromises the grommet seal
AirlocksAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. are consumables. A fresh airlockAirlock A one-way valve fitted to the fermenter lid that allows CO₂ produced during fermentation to escape while preventing air and contamination from entering. Filled with sanitiser solution or cooled boiled water. The rate of bubbling gives a rough indication of fermentation activity, but the absence of bubbling does not confirm fermentation is complete — gravity measurement is the reliable indicator. 3-piece and S-type designs are both common and functionally equivalent for homebrew use. costs less than a ruined batch.