Polyethylene terephthalate (PET)

	ABNS	DES	Cleaning	Beer/wort
Rating	A	A	A†	A

The Cleaning column aggregates all cleaning product categories at working concentrations. PET has the most differentiated cleaning profile in this register — see the Cleaning compatibility section for a full breakdown by cleaner type.

PET is a semi-crystalline thermoplastic polyester. It is the material of carbonated soft drink and soda bottles, and appears in homebrewing as pressure fermenters (FermZilla All-Rounder), carboys, mini kegs (Oxebar), and beer bottles. Its backbone consists of alternating terephthalate aromatic rings and ethylene glycol units connected by ester linkages (–CO–O–). Those ester linkages are the material's primary chemical vulnerability: both acid and alkaline conditions attack the ester bond through hydrolysis, regenerating terephthalic acid and ethylene glycol. The rate of hydrolysis depends strongly on pH, temperature, and contact duration — and PET's temperature sensitivity is substantially greater than that of the polyolefins (PP, HDPE) elsewhere in this register.

This page is about PET the material, not about specific products. The FermZilla All-Rounder, Oxebar kegs, and PET beer bottles are cited as evidence for material behaviour and as sources for manufacturer cleaning guidance. The conclusions apply to PET articles generally. Barrier PET constructions (Oxebar) differ from plain PET in ways that matter — that distinction is set out in Barrier PET — Oxebar construction and cleaning and maintained throughout.

Identifying PET

Look for the Resin Identification Code moulded into the base of the article — three chasing arrows forming a triangle, with the number 1 inside and PET or PETE below.

Resin Identification Code 1 — PET (Polypropylene)

The RIC 1 symbol as it appears on the base of PET articles.

RIC symbol: Anton Poliakov, Wikimedia Commons, CC BY-SA 4.0. Modified: fill colour adapted for dark-mode display.

PET is clear and colourless at typical wall thicknesses, or amber-tinted where UV protection is added. It is rigid, glossy, and fractures cleanly under impact rather than yielding. The RIC 1 code is the most reliable identifier; in practice, any transparent, lightweight, rigid brewing vessel with a ♺1 marking on the base is almost certainly PET.

Images

Images showing typical PET articles in a homebrewing context — a FermZilla pressure fermenter body, a PET carboy, an Oxebar keg, a PET beer bottle, and the RIC 1 marking — are planned for this section.

Food grade status

PET has the most thoroughly documented food contact compliance ecosystem of any plastic in this register. That depth of documentation is driven by the global beverages industry, which packages beverages — both carbonated and non-carbonated — in PET at volumes measured in millions of tonnes annually.

Under EU Regulation 10/2011, PET is a positively listed polymer with established specific migration limits for its monomers: terephthalic acid (SML 7.5 mg/kg) and ethylene glycol (SML 30 mg/kg). Both monomers have well-characterised toxicology profiles and are tested routinely in food contact applications.

The compliance testing context carries important practical weight. PET beverage bottles contact phosphoric acid (pH 2.5 in cola), citric and ascorbic acid (pH 2.0–2.5 in lemon and lime juice), citric acid (pH 2.5–3.5 in citrus drinks), and carbonic acid for weeks to months on retail shelves, often at temperatures above fermentation cellar conditions. That is a more aggressive contact scenario than any sanitiser or beer contact in homebrewing. Commercial producers obtain Declarations of Conformity for their PET packaging under 10/2011 routinely — and homebrewers benefit indirectly from that compliance infrastructure when sourcing bottles and vessels from the same supply chains.

For Oxebar barrier PET, the food contact surface is PET throughout — the barrier polymer component is dispersed within the PET matrix and not independently in food contact.

The full food contact compliance framework — what makes an article food grade, GMP requirements, EU simulant testing, DoC structure, and what to do without one — is covered on the Food contact compliance page. The sections below cover only what is specific to PET.

What makes a PET article food grade?

As with all thermoplastics, the polymer backbone is not the concern. PET's monomers are well-regulated and the migration limits are achievable and routinely met. The distinction between food grade and industrial grade PET lies in the additive package — antioxidants, processing stabilisers, and any colourants must be from the EU 10/2011 approved list.

The RIC 1 code identifies the polymer class, not food grade status or GMP compliance. A food grade PET bottle and an industrial PET component may both carry RIC 1.

DoC availability for PET brewing articles

PET brewing articles from the homebrewing market typically carry a food grade claim but no publicly available DoC — consistent with the pattern across the register. Where PET is sourced from food packaging supply chains (commercial beverage bottles), DoCs are more readily obtainable. If sourcing PET bottles for homebrew use from a packaging supplier rather than a homebrew retailer, a DoC referencing EU 1935/2004 and 10/2011 should be obtainable on request.

Temperature limits

Temperature is the defining operational constraint for PET, and the one that most distinguishes it from the polyolefins. It governs all three use contexts differently.

Continuous use

PET performs well across the full range of fermentation and conditioning temperatures. Standard ale and lager fermentation (8–22 °C) presents no concern. High-temperature fermentation with Kveik and other thermophilic yeasts nominally runs up to 38–40 °C, which is at the material's limit rather than comfortably within it. Two practical considerations apply: active fermentation generates heat above ambient, so the vessel wall temperature can exceed the ambient temperature you're targeting; and heat sources applied directly to the vessel — heat belts, heat mats, or heat pads in contact with the PET body — are not recommended, as they can create localised hot spots above the bulk temperature. If you're fermenting warm with Kveik, consider whether a glass, HDPE, or stainless vessel is the better choice. Rated A for standard fermentation and conditioning temperatures; approach the upper limit with awareness.

Cleaning

40 °C maximum for any cleaning solution. This is the limit confirmed by KegLand for FermZilla PET vessels¹ and is consistent with the hydrolysis kinetics of PET in alkaline media. At 40 °C, alkaline cleaners remain slow enough to be safe at practical contact times. At 60 °C — standard for stainless CIP — ester hydrolysis in alkaline solution accelerates dramatically: visible surface cloudiness and structural degradation begin within the relevant contact window.

The 40 °C limit applies to the temperature of the cleaning solution, not to ambient temperature. Fill PET vessels with cleaning solution prepared at or below 40 °C. Do not fill hot and assume the vessel will protect itself as it cools.

For Oxebar barrier PET, KegLand's stated maximum is 45 °C², but cleaning practice should remain at 40 °C — the barrier polymer matrix or inter-layer bond is at additional risk from elevated temperature, and the 5 °C margin provides no justification for relaxed discipline.

Hot liquid contact — never

Never fill a PET vessel with hot wort, hot sparge water, or any liquid above 40 °C. This applies to PET beer bottles, FermZilla-type pressure fermenters, and Oxebar kegs without exception.

PET's heat deflection temperature under load sits in the range 65–80 °C depending on grade and crystallinity. Near-boiling wort causes immediate, irreversible deformation. Wort at 50–60 °C poses a deformation risk under the internal pressure of a sealed vessel even before the HDT is reached.

No-chill brewing is not compatible with PET. No-chill relies on transferring hot wort directly into a sealed vessel and allowing it to cool slowly. This exposes the vessel wall to temperatures that will degrade PET. For no-chill-compatible vessel materials, see the no-chill process page. PET vessels should not be adapted for no-chill use regardless of design.

Comparison to polyolefins

PP and HDPE tolerate hot wort and hot cleaning solutions that are entirely off-limits for PET. Temperature constraint is one of PET's meaningful practical limitations relative to those materials. The trade-off is optical clarity, lower wall thickness at equivalent strength, and better intrinsic gas barrier performance than either polyolefin.

Compatibility — ABNS: A

Working-dilution ABNS sanitiser (StellarSan, Star San, Sanipro Rinse, and equivalents) is compatible with PET. Both active components are considered separately.

Phosphoric acid component. PET rates A for dilute phosphoric acid at ambient temperature. At pH 3.0–3.5 and 20 °C, the ester hydrolysis rate is negligible in any brewing-relevant timeframe. The commercial context confirms this: PET beverage bottles contact phosphoric acid (pH 2.5 in cola) for weeks to months at retail without degradation. Working-dilution ABNS at pH 3.0–3.5 for 30–60 seconds contact is a far less demanding scenario. The ISM chemical compatibility chart rates PET as A for phosphoric acid, consistent with this.³

DDBSA component. DDBSA (the anionic surfactant in ABNS products) interacts with PET through a mechanism specific to PET among the polyolefins: pi–pi stacking between DDBSA's aromatic ring and the terephthalate rings in the PET backbone. Unlike PP and HDPE — which contain no aromatic rings and resist DDBSA through their crystalline structure alone — PET's terephthalate rings can participate in weak non-covalent pi–pi interactions with the dodecylbenzene component of DDBSA.

This interaction is the same in family as the mechanism that makes polystyrene significantly more vulnerable to DDBSA — covered in detail on the PS/SAN page. PET's susceptibility is substantially lower than PS for two reasons: the terephthalate rings are incorporated into the main chain (more sterically hindered than PS's pendant phenyl groups), and PET's semi-crystalline structure limits access to the susceptible amorphous regions.

At working dilution in a sealed vessel — whether for a 60-second sanitisation cycle or stored dilute ABNS left in the tank between sessions — the interaction is minor and reversible. The key point is concentration: at working dilution, DDBSA remains at approximately 300 ppm and pH stays around 3.0–3.5, conditions under which ester hydrolysis is negligible and pi–pi stacking interaction is minimal. No structural consequence, no concern.

Under WDC cycling — where ABNS residue concentrates progressively on surfaces that dry between uses — the concern is real but modest at Zone A — open surfaces (fermenter interior walls, bottle interior). At Zone B — confined geometry (thread roots, lid seal channels, tap fittings), concentrated DDBSA residue has sustained contact with the surface at an elevated effective concentration, which warrants periodic inspection for surface cloudiness or micro-crazing.

The WDC model and zone definitions are set out on the WDC model page. For PET pressure vessels with fittings, Zone B is the primary location to monitor over service life.

WDC accumulation chart — planned

A quantified WDC cycle analysis for PET — showing DDBSA and phosphoric acid accumulation by zone against the concern threshold, equivalent to the PP page chart — is planned for this section. This requires confirming PET-specific ESC threshold data.

Structural vs migration. These are distinct concerns. The WDC-driven DDBSA accumulation at Zone B is a structural concern — concentrated surfactant at a mechanically stressed interface risks ESC, not a migration event. Migration of PET monomers into beer is a separate question governed by the food contact compliance framework: at homebrewing temperatures and contact times, migration from compliant undamaged PET is a fraction of the conservative EU simulant test conditions. A damaged PET surface — one showing cloudiness, crazing, or dimensional change — has an unknown, not necessarily elevated, migration profile, and should be retired.

The DuoTight case study — in which DDBSA WDC accumulation caused progressive structural failure in POM fittings — illustrates the structural failure mechanism. POM and PET fail through different chemical routes, but the structural concern (Zone B geometry, concentrated residue, mechanical load) is the same in family. See the DuoTight case study for the worked WDC failure analysis.

Practical guidance. Use ABNS for PET sanitisation as intended — fill or coat, maintain contact time, drain. Rinse any spills from external surfaces promptly; dried ABNS residue on exterior threads and fittings contributes to WDC accumulation. Clean the vessel after use to reset the WDC cycle before the next brew. Stored dilute ABNS in a sealed vessel does not create WDC conditions — concentration stays at working dilution without evaporation — so leaving dilute ABNS in the tank between sessions is chemically safe for the PET. The better argument for making fresh solution each time is efficacy: dilute ABNS loses sanitising effectiveness as the peroxy equilibrium shifts over days. Make what you need, when you need it.

Compatibility — DES: A

DES (ethanol-based sanitiser) at 70–80% has no meaningful interaction with PET at typical contact times. PET is rated for ethanol at all concentrations encountered in homebrewing use. No concern.

Compatibility — cleaning: A†

PET has the most complex cleaning compatibility profile in this register. The three cleaner categories behave differently. The constraints on PET pressure fermenters and kegs are stricter than for plain PET bottles, but the reason is not the PET material itself — it is geometry and mechanical stress. A PET soda bottle stores carbonated beer without issue. The difference with a pressure fermenter is one of stress geometry and sustained mechanical load: pressure vessel fittings — threaded ports, lid threads, O-ring seats under torque — create Zone B geometry where cleaner can concentrate and dwell, and sustained CO₂ pressure creates ESC-relevant mechanical stress. A PET bottle does have a threaded neck and geometric transitions, but it operates at lower sustained pressure, the thread is single-use or low-cycle, and there are no O-ring interfaces under sustained compression. The risk profile differs in degree, not in kind.

The sequence is always clean first, then sanitise. Rinse cleaning solution thoroughly from PET vessels before applying ABNS.

Oxidising cleaners (StellarOxy, ChemiPro OXI) — A

KegLand explicitly recommends StellarOxy¹ as the primary cleaner for FermZilla PET fermenters, and oxidising percarbonate cleaners (StellarOxy, ChemiPro OXI) are the preferred cleaning choice for PET across all vessel types. They work through an oxidative mechanism that does not attack ester linkages preferentially, and are effective on beer residues at cold and warm water temperatures with no contact time restriction beyond the 40 °C maximum that applies to all PET cleaning.

For standard fermentation soiling — yeast cake, beer film, light protein deposits — extending the StellarOxy soak to 30–60 minutes with agitation is more effective than the default 15–20 minutes. For very heavy soiling, a second fresh solution is more effective than extending a single soak beyond 60 minutes, as the active hydrogen peroxide is consumed and the remaining solution is weakly alkaline sodium carbonate with little oxidative activity. For heavy hop resin accumulation specifically — which requires alkaline saponification rather than oxidation — StellarClean (with the 30-minute PET time limit) is genuinely the better tool; extended StellarOxy does not fully substitute.

High-metasilicate alkaline cleaners (StellarClean, ChemiPro Wash, ChemClean) — A*

Alkaline cleaners containing significant sodium metasilicate — StellarClean, ChemiPro Wash, ChemClean — are conditionally suitable for PET at cold or warm water temperatures (≤40 °C), with a 30-minute maximum contact time and immediate, thorough rinsing afterwards.

The 30-minute limit is not arbitrary. At working concentration and ambient temperature, measurable surface changes begin on PET around this window — cloudiness and the onset of detectable ester hydrolysis. In practice, 15–20 minutes with moderate agitation is sufficient for typical beer residue on most PET surfaces, leaving margin before the limit. KegLand's FermZilla All-Rounder cleaning guide¹ is explicit: "Do not leave StellarClean in the vessel for longer than 30 minutes as this can damage the tank." For heavy soiling where a longer soak is needed, KegLand's guidance is to switch to StellarOxy, which may be left overnight.¹ KegLand's Oxebar cleaning video⁴ is stricter still: "Do not over-soak: Limit detergent contact to a maximum of 15 minutes to protect the plastic."

The 30-minute limit applies at ambient temperature. Do not use these cleaners hot on PET: the combination of pH >12 and elevated temperature accelerates hydrolysis significantly beyond what the time limit provides protection against.

Within stated limits only — exceeding the contact time or temperature degrades this rating rapidly.

Phosphate-based alkaline cleaners (Grainfather High Performance Cleaner) — A

Grainfather High Performance Cleaner uses sodium tripolyphosphate (STPP) as its primary alkaline agent rather than sodium metasilicate. STPP is a milder alkaline agent than metasilicate at equivalent concentration, and the phosphate-based formulation presents no ester hydrolysis concern for PET at homebrewing concentrations and contact times. Rating: A, no contact time restriction beyond the 40 °C maximum that applies to all PET cleaning.

Five Star PBW — A*

KegLand StellarClean and Five Star PBW

KegLand markets StellarClean as Powerful Brewery Wash (PBW); Five Star makes a separate product, Powdered Brewery Wash. Both use the abbreviation — in this section PBW means Five Star's product. StellarClean is rated separately above.

Five Star PBW is a high-metasilicate alkaline cleaner in the same category as StellarClean. KegLand's cleaning guide does not list it — but KegLand recommends their own products throughout their documentation, and the absence of a mention is not a recommendation against. PBW's formulation varies by market: EU-market labels show sodium metasilicate at 20–35%, which is comparable to or higher than StellarClean. It should be treated identically: A* with the same 30-minute contact time limit on PET, cold water, immediate rinsing. The same logic applies as to StellarClean — effective for heavy soiling, but StellarOxy is the lower-risk default for routine cleaning.

StellarOxy as a single cleaner for mixed PET and polyolefin equipment

If your brewery uses both PET vessels (FermZilla, Oxebar, PET bottles) and polyolefin vessels (PP buckets, HDPE cubes), StellarOxy is the better single-cleaner choice for the whole fleet. It is unrestricted on all of them. StellarClean and Five Star PBW are more powerful on heavy protein and hop soiling but introduce PET-specific time discipline and the risk of forgetting which vessel you are cleaning. StellarOxy handles standard beer residue effectively for most homebrewing scenarios; for sessions with heavy trub or hop matter, 15–20 minutes with agitation is usually sufficient. The only scenario where a metasilicate cleaner adds meaningful value is persistent soiling that percarbonate genuinely cannot shift — and even then, switching for that specific clean (with discipline) is preferable to using it routinely on PET.

Why three cleaner categories behave differently on PET

Pure percarbonate cleaners work oxidatively with minimal ester hydrolysis risk. High-metasilicate cleaners — StellarClean, ChemiPro Wash, Five Star PBW — add a strong alkaline component that begins attacking ester linkages above the 30-minute threshold. The mechanism is the same across all three; the time limit applies equally.

† PET cleaning: unrestricted (A) for oxidising cleaners. Conditional (A*) for high-metasilicate alkaline cleaners (StellarClean, ChemiPro Wash, Five Star PBW) within a 30-minute contact limit at ≤40 °C.

Compatibility — beer/wort: A

Beer at fermentation and storage conditions

Beer at pH 4.0–4.5, 4–8% ABV, at 0–40 °C for weeks to months: A. This is exactly the condition under which PET beverage packaging operates commercially, including beer. No material concern across the full fermentation temperature range, including high-temperature Kveik fermentation approaching 40 °C.

Sour beer

Lactic acid and acetic acid at sour beer concentrations (pH 3.2–3.8) present no additional concern beyond what standard beer contact covers. The acid hydrolysis rate at sour beer pH and fermentation temperatures is negligible over any practical timescale. A.

Wort — temperature governs

Wort at pitching temperature (18–22 °C, or up to 38–40 °C for Kveik) contacts PET as a matter of routine in PET fermenters — no concern. Hot wort above 40 °C is incompatible with PET for structural reasons set out in Temperature limits. No-chill is off-limits regardless of intent. A at pitching temperature; X above 40 °C.

Oxygen ingress

Oxygen ingress through the PET wall is a material property, not a compatibility issue. It is relevant because it sets a practical shelf-life ceiling for certain styles packaged in standard PET.

For a 500 mL standard PET bottle, the oxygen transmission rate (OTR) is approximately 0.04–0.08 mL O₂/day at ambient conditions — approximately 1.1–2.2 mL cumulative over four weeks of bottle conditioning. Robust stouts, strong ales, and malt-forward styles tolerate this level of ingress; residual yeast activity and the beer's own reducing chemistry partially compensate. Hop-forward and haze-forward styles — IPAs, pale ales, and especially New England IPAs (NEIPAs) — are sensitive to oxidation at this scale. NEIPAs are arguably the most susceptible style in common homebrewing: high dry hop load, haze-forming proteins that interact readily with oxygen, low bitterness that masks nothing, and typically consumed young when any oxidation damage is immediately apparent. Standard PET bottle conditioning imposes a practical shelf-life limitation for these beers regardless of packaging hygiene.

UV transparency and skunking

Standard PET is UV-transparent. This has two practical consequences:

For fermenters (pro): optical clarity lets you observe fermentation activity, yeast settlement, and clarity development without opening the vessel. This is a genuine advantage over opaque PP or HDPE fermenters.

For packaging (con): UV and short-wavelength visible light (350–500 nm) degrades iso-alpha acids in hopped beer through a radical reaction, producing 3-methyl-2-butene-1-thiol (3-MBT) — the compound responsible for the "skunked" off-flavour. 3-MBT has a detection threshold of approximately 4 parts per trillion; even brief light exposure is enough to cause detectable damage in sensitive styles. Clear PET bottles offer no protection against this mechanism. Lager, pale ale, and NEIPA are the most susceptible styles; dark beers with low iso-alpha acid content are less affected.

Amber-tinted PET — used in the 20L Oxebar — absorbs the damaging wavelengths and provides meaningful light protection. If using clear PET bottles or kegs for light-sensitive styles, store them in darkness or use opaque sleeves.

UV degradation of PET itself: UV also degrades the PET material over time through photo-oxidation, causing yellowing and embrittlement. KegLand explicitly note that keeping FermZilla vessels out of direct sunlight is essential.⁵ This is a separate concern from skunking — the vessel itself is being damaged, not just the beer. Store all PET fermenters and kegs away from direct sunlight as a matter of routine.

Oxebar — barrier PET as a packaging solution

Oxebar naming — the same material, several names

Oxebar was originally a separate Australian company (Oxebar Australia) specialising in polymer containers and oxygen barrier packaging technology. The brand and technology were absorbed into KegLand, and "Oxebar" is now KegLand's product line name for their barrier PET keg range.

All current Oxebar keg products — 4L, 8L, and 20L — appear to use the same construction: a PET polymer blend with barrier properties, claimed by KegLand to give approximately 3× better oxygen barrier than standard PET.²⁶ KegLand use at least three names for this across their product pages: Oxebar Mono, Oxebar Monolayer, and Mono Barrier PET Polymer Matrix. All three appear to describe the same material. The 4L ball lock tapping draught pack is the same keg bundled with a tapping head — the vessel itself is identical. Confirmation from KegLand of the barrier polymer composition would be welcome.

The Oxebar range is the practical homebrewing answer to PET oxygen ingress. The table below compares recommended storage duration for Oxebar (Mono/Monolayer) against estimated shelf life for standard PET bottles, by style and storage temperature. Oxebar figures are from KegLand's product documentation.² Standard PET estimates are derived from the OTR data above and are not from a manufacturer source.

Beer style	Standard PET — cold (2 °C)	Standard PET — ambient (25 °C)	Oxebar Mono — cold (2 °C)	Oxebar Mono — ambient (25 °C)
Light coloured, hazy, hoppy (incl. NEIPA)	~3–4 weeks	~1–2 weeks	6 months	2 months
Amber beers, porters, summer ales	~6–8 weeks	~2–3 weeks	9 months	3 months
Dark beers, stouts, triples	~3–4 months	~4–6 weeks	15 months	5 months

Choosing between packaging options — standard PET, Oxebar, glass, or stainless keg — is covered in the packaging guide.

PET vs PP and HDPE as fermentation vessels

Oxygen ingress is not just a packaging concern — it also matters during fermentation and conditioning when beer sits in the vessel for weeks. This is where PET offers a meaningful advantage over PP and HDPE fermenters. KegLand state explicitly that the FermZilla's PET wall is a better gas barrier than PP or HDPE,⁷ and that HDPE fermenters can be porous enough to carry flavour and aroma from one batch to another.⁵ Standard PET OTR is already substantially lower than HDPE at typical wall thicknesses; the practical implication for a homebrewer keeping beer in a fermenter for 2–4 weeks is real, if modest. For closed-transfer brewing with pressure fermentation and kegging, PET's oxygen barrier is a genuine advantage over HDPE or PP buckets.

Stainless steel is effectively impermeable to oxygen and remains the reference standard. For long conditioning periods or oxygen-sensitive styles, a PET pressure fermenter closed under CO₂ is the practical plastic alternative.

Barrier PET — Oxebar construction and cleaning

The Oxebar construction variants and their implications for cleaning compatibility are covered here. Barrier performance and packaging choice are discussed under Oxygen ingress above.

Construction

KegLand describe Oxebar as a PET polymer blend — their PCO38 kegs video⁶ refers to PET and nylon being blended together, though this is a simplified marketing description rather than a technical specification. The specific barrier polymer, its grade, and the precise blend composition have not been confirmed by KegLand in formal documentation. What is confirmed from KegLand's own sources is that Oxebar is a single-layer polymer blend (not a laminate), and that the food contact surface is PET throughout.

Chemical compatibility

Chemical compatibility analysis is identical to plain PET for all Oxebar constructions: the same 40 °C temperature limit, the same cleaner ratings, the same ABNS profile. The barrier polymer component is within the PET matrix and not independently in food contact. Based on available information, the blend has good general chemical resistance at homebrewing concentrations — no additional compatibility concern has been identified, but KegLand confirmation of the specific barrier polymer would allow this to be stated with more precision.

The additional constraint for Oxebar

The barrier polymer component in the Oxebar blend may respond differently to elevated temperature or sustained alkaline exposure than plain PET. This is an additional reason to hold strictly to 40 °C maximum for Oxebar cleaning, separate from the plain-PET hydrolysis concern. KegLand's stated 45 °C maximum² is a ceiling, not a target.

ESC and pressure — structural failure risk

Pressure vessel safety — applies to all materials

This section discusses structural failure risk in the context of PET, but the underlying safety principles apply to all pressurised vessels regardless of material — PET fermenters and PET bottles (this page), glass bottles (material), stainless kegs (material). Pressure vessel failure can cause serious injury. The material determines how and when failure may occur; the consequences of failure are determined by the pressure stored. This topic is covered on each relevant material page and in the equipment guides. A dedicated pressure safety overview is planned.

PET pressure vessels used under CO₂ introduce a structural failure risk not present in atmospheric-use articles. This distinction matters: structural failure in a pressurised vessel is a physical safety concern, not just a material or flavour concern. A cracked or burst PET pressure vessel under carbonation pressure can cause injury.

Environmental stress cracking requires both a susceptible material and sustained mechanical stress. The pressure level varies significantly by vessel type and filling method — and not always in the direction you might expect:

Force-carbonated keg: regulated pressure, typically 10–15 PSI at serving temperature. Controlled by the gas regulator (which has its own PRV) and the keg's own PRV. Constant and well-bounded — assuming the regulator is set correctly and the PRV is clean and functional.
Pressure-fermented FermZilla: CO₂ generated by fermentation, controlled by a spunding valve set to the target pressure and a PRV as a safety ceiling (typically 10–15 PSI). Both devices together keep pressure within a defined, safe range — assuming both are set correctly, free of krausen or debris that could cause them to stick, and functioning as intended.
Bottle filled from keg: same dissolved CO₂ as the keg at filling, but once sealed the pressure is unregulated — determined by headspace volume and temperature. No PRV, no pressure relief of any kind.
Bottle-conditioned PET bottle: priming sugar generates CO₂ with no pressure relief whatsoever. Pressure is determined entirely by the amount of fermentable extract, temperature, and headspace. There is no spunding valve, no PRV, no regulator — nothing between the bottle and failure except the structural limit of the vessel itself. Over-primed or warm bottle-conditioned PET bottles can and do fail catastrophically — "bottle bombs" are a well-documented homebrewing hazard. This is where ESC risk is greatest for PET specifically, and where the consequences of structural failure are most serious.

Chemical stress compounds mechanical stress. DDBSA residue accumulation at Zone B — confined geometry interfaces (O-ring seats, lid threads under torque) and Zone C — compressed contact under sustained stress geometries adds chemical susceptibility on top of mechanical load.

Hydrostatic testing. KegLand strongly recommends periodic hydrostatic testing of both Oxebar kegs² and FermZilla pressure fermenters — every two years, with a full test procedure in their Hydro Test Guide.⁸ The test is done with the vessel filled to the brim with water (not CO₂ or air — water is incompressible, so a failure during the test is safe). Given the low cost of Oxebar kegs, replacing them on the two-year schedule rather than retesting is a reasonable alternative. For FermZilla fermenters, note that the tank has a stamped date — do not use under pressure past that date without hydrotesting first.

Practical implications:

Inspect thread interfaces, lid seals, and O-ring seats for cloudiness, crazing, or micro-cracking at each brew
Retire any vessel showing visible surface degradation at a stressed interface — if you see cloudiness, crazing, or deformation, replace it. The compliance testing was done on undamaged material; for damaged PET the migration risk is low (the products are terephthalic acid and ethylene glycol, both with established SMLs) but unquantified. When in doubt, replace rather than continue using.
Replace O-rings and lid seals on the manufacturer's schedule, not at first leakage
Follow KegLand's two-year hydrostatic test schedule for Oxebar kegs and FermZilla fermenters
For bottle-conditioned PET bottles: accurate priming calculations, consistent fermentation temperature, and conservative headspace reduce pressure uncertainty

PET in homebrewing — the practical picture

PET is a well-founded fermentation and packaging material within its operational limits. Its food contact credentials are the strongest of any plastic in this register, backed by decades of commercial beverage packaging data. Within the temperature envelope, it performs reliably across all brewing chemicals encountered in good practice.

Where PET excels. Packaging: PET beer bottles are the standard alternative to glass at homebrew scale — lighter, shatterproof, and food contact compliant from well-documented supply chains. PET pressure fermenters: optically clear, lightweight, and chemically compatible with the full brewing process within temperature limits. Oxebar barrier PET kegs: the improved barrier matrix meaningfully extends shelf life for sensitive styles versus standard PET bottles.

Migration. PET's monomers — terephthalic acid (SML 7.5 mg/kg) and ethylene glycol (SML 30 mg/kg) — are among the best-characterised food contact migration products in the plastics register. Both limits are set accepting low-level migration and routinely met by compliant PET packaging. EU 10/2011 simulant testing is conducted at 60 °C over 10 days — conditions more aggressive than any homebrewing scenario. At fermentation temperatures and conditioning periods, actual migration from undamaged, compliant PET is a fraction of those test-condition figures. The open question — as with all plastics — is whether repeated cleaning and sanitising contact slowly depletes or alters the additive package over many cycles; this has not been characterised for homebrewing conditions. If the vessel is visibly undamaged and sourced from a food-contact supply chain, migration is not a meaningful concern. If it shows visible damage — cloudiness, crazing, deformation — retire it. The compliance data no longer applies to a damaged surface.

Where the constraints bind. The 40 °C temperature ceiling is a hard limit. No hot wort, no hot cleaning solutions, no no-chill. For any brewing practice that requires hot liquid contact with the vessel, stainless steel or rated HDPE is the correct choice. The cleaning protocol — StellarOxy as default, metasilicate cleaners with 30-minute discipline for heavy soiling — requires more attention than the single-cleaner approach appropriate for polyolefins or stainless. Oxygen ingress limits standard PET's suitability for long-term storage of sensitive styles; Oxebar barrier PET addresses this.

Cleaning and sanitising PET in practice. Use StellarOxy (or ChemiPro OXI) as the routine cleaner. Fill to coverage, agitate, allow 15–20 minutes, drain and rinse thoroughly. Apply ABNS after rinsing; fill the vessel, allow 1 minute contact, drain (no rinse needed for no-rinse formulations at label dilution). Store dry between uses.

Assessing and retiring equipment

PET vessels are transparent, which is a genuine advantage — surface condition, scratching, and early damage are all visible in a way they are not on opaque HDPE or PP. Use that visibility actively: inspect at each brew, not just when something looks wrong.

Ester hydrolysis cloudiness. The most PET-specific failure signal. Alkaline cleaner overexposure or hot liquid contact causes ester hydrolysis at the PET surface, which presents as a persistent milky cloudiness or loss of optical clarity in the affected area. Unlike hard water scale or beerstone, it cannot be removed by acid rinsing — it is a structural surface change, not a deposit. It typically appears first in the areas of greatest chemical exposure: base of the vessel (where cleaning solution pools), and around threaded ports. If cloudiness is present and does not clear after a thorough rinse, the surface has been chemically degraded. Retire the vessel.

ESC crazing at Zone B and C interfaces. Thread roots, O-ring seats, and lid thread grooves are the locations to look most carefully. Early ESC presents as a fine network of surface cracks or a faint haze — similar to the ester hydrolysis cloudiness but localised to geometrically stressed areas. Inspect with a torch held at a low angle to the surface — oblique lighting reveals fine cracks that are invisible under flat overhead light. At Zone C (compressed O-ring interfaces), look for deformation of the groove geometry. Any visible crazing, cracking, or dimensional change at a stressed interface means the vessel should not be used under CO₂ pressure. Retire it.

Mechanical scratching. Clean PET with a soft cloth or sponge only — no brushes, no abrasive pads. PET scratches more readily than HDPE. Scratches create surface texture that traps biofilm and is not reliably reached by sanitising chemistry. A scratched interior that cannot be restored to a clean, smooth finish after a thorough cleaning soak has exceeded its useful service life.

UV embrittlement. KegLand explicitly note that FermZilla vessels must be kept out of direct sunlight.⁵ UV degrades PET progressively through photo-oxidation: the surface yellows, becomes brittle, and loses mechanical strength. A yellowed or brittle PET vessel stored in direct sunlight should not be used under pressure. Amber-tinted PET (Oxebar 20L) has better UV resistance — but the same principle applies: store all PET equipment away from direct sunlight as a matter of routine.

Warping or deformation. Any distortion of a lid, base, or vessel wall that prevents correct seating, alignment, or sealing. Usually caused by hot liquid contact or sustained mechanical load above the temperature limit. Retire immediately — deformed PET is a structural failure risk under pressure.

Pressure vessel principle. The compliance testing on which food contact safety is based was conducted on undamaged, GMP-manufactured PET at defined conditions. Once a vessel shows visible damage — cloudiness, crazing, cracking, deformation — the compliance data no longer applies. The risk is not necessarily elevated; it is unknown. For pressure fermenters and mini kegs, a vessel with unknown structural integrity is a safety risk — CO₂ pressure failure can cause serious injury. Retire it. The cost of an Oxebar keg or FermZilla tank is not the cost of that consequence.

Summary by article type — scenarios

Scenario	Rating	Conditions
Beer contact (fermentation / storage, 0–40 °C)	A	No restriction — commercial beverage standard
Wort at pitching temperature (18–22 °C)	A	No concern
Hot wort or any liquid >40 °C	X	Never — HDT, hydrolysis, deformation risk
No-chill wort transfer	X	Not compatible with PET — see the no-chill process page
ABNS — brief sanitisation contact (30–60 sec)	A	Ambient temperature; drain; no restriction
ABNS — Zone A open surfaces, WDC cycling	A	Low concern; periodic inspection
ABNS — Zone B confined geometry, WDC cycling	B	Pi–pi stacking mechanism; monitor for surface change at threads and seal grooves
DES (70–80% ethanol)	A	No restriction at typical contact times
Oxidising cleaner (StellarOxy, ChemiPro OXI)	A	Preferred cleaner; no time restriction at ≤40 °C
High-metasilicate alkaline cleaner (StellarClean, ChemiPro Wash, Five Star PBW)	A*	30-minute hard limit; ≤40 °C; rinse immediately
Sour beer (pH 3.2–3.8, lactic / acetic dominant)	A	No restriction

* A within stated conditions. Exceeding the contact time or temperature degrades this rating significantly.

Rating key: A = unrestricted within stated conditions · B = suitable with precautions; monitor over service life · C = manufacturer advises against; use alternatives · X = not suitable

Summary by article type

Article	Food grade	Temp limits	ABNS WDC	Cleaning
PET beer bottles	RIC 1 confirmed. DoC obtainable from packaging supply chains.	40 °C max cleaning; no hot wort or hot fill.	Zone A — low concern at interior surfaces.	StellarOxy preferred; StellarClean ≤30 min; Five Star PBW A* with same limit.
PET pressure fermenter (FermZilla All-Rounder)	Food grade PET confirmed by manufacturer. No DoC publicly retrieved.	40 °C max cleaning hard limit; no hot wort.	Zone B at thread interfaces — inspect for surface change. ESC risk under pressure; follow hydrostatic test schedule.	StellarOxy preferred; StellarClean ≤30 min; Five Star PBW A* with same limit.
Oxebar keg	Barrier PET polymer blend; food grade claim by manufacturer.	40 °C max.	Zone B at fittings; same as fermenter.	Same as PET fermenter. KegLand video guidance: 15 min max soak.⁴
PET sanitiser reservoir / spray bottle	Functional use only — not beer contact.	Ambient use.	N/A	N/A

KegLand, FermZilla All-Rounder User Guide / Cleaning. Accessed May 2026. Direct quotes: "If using StellarClean it is important to limit contact time to 30 minutes"; "Do not leave StellarClean in the vessel for longer than 30 minutes as this can damage the tank"; for heavy soiling, overnight soak with StellarOxy only. Water temperature limit: less than 40 °C. ↩ ↩² ↩³ ↩⁴
KegLand, 4L Oxebar Keg with Cap and Handle (PCO38). Accessed May 2026. Confirms: do not exceed 45 °C; two-year hydrostatic testing required. Product described as Oxebar Mono/Monolayer in product text despite "multilayer" in URL. ↩ ↩² ↩³ ↩⁴ ↩⁵
ISM Industrial, Chemical Compatibility Chart — Polyethylene Terephthalate (PET). ISM's scale: A = Excellent, B = Good/minor effect, F = Fair, D = Severe effect — their A maps to this guide's A, their D to this guide's X. Rates PET as A for phosphoric acid. Covers bulk chemical exposure and does not distinguish Zone A, B, and C conditions as defined in the WDC model. ↩
David Heath / KegLand, Oxebar Mini Keg — How to Clean (YouTube), youtube.com/watch?v=ikk99JCE3pM. Accessed April 2026. Direct quote at 0:01: "Do not over-soak: Limit detergent contact to a maximum of 15 minutes to protect the plastic." Also confirms: no bleach or high-caustic cleaners; no sodium metasilicate at extended contact. ↩ ↩²
KegLand, FermZilla 30L All-Rounder product page. Accessed May 2026. Direct quote: “Other HDPE fermenters tend to be so porous they carry flavour and aroma from one batch to another.” ↩ ↩² ↩³
KegLand, Best Value Kegs System EVER — PCO38 Kegs (YouTube, 2022). Describes Oxebar construction as "PET and Nylon that is blended together" to reduce oxygen and CO₂ transmission rate. Also describes the nylon as distributed within the PET ("bits of nylon distributed within the PET"; "layered nylon PET"). Confirms oxygen diffuses through the wall regardless of internal pressure. ↩ ↩²
KegLand, FermZilla All-Rounder User Guide. Accessed May 2026. Direct quote: “The PET plastic is not permeable like some other fermenters made from PP or HDPE. The fermenter wall is a much better gas barrier keeping your product fresher for longer.” ↩
KegLand, FermZilla All-Rounder Hydro Test Guide. Full test procedure: fill vessel to brim with water, pressurise to 4.0 bar (60 PSI) using regulated water or CO₂ source, hold 1 minute. Use grey 6.5 bar PRV during test; swap back to red 2.5 bar PRV immediately after. FermZilla has a stamped date 24 months after manufacture — do not use under pressure past this date without passing a hydro test. ↩

Identifying PET​

Food grade status​

What makes a PET article food grade?​

DoC availability for PET brewing articles​

Temperature limits​

Continuous use​

Cleaning​

Hot liquid contact — never​

Compatibility — ABNS: A​

Compatibility — DES: A​

Compatibility — cleaning: A†​

Oxidising cleaners (StellarOxy, ChemiPro OXI) — A​

High-metasilicate alkaline cleaners (StellarClean, ChemiPro Wash, ChemClean) — A*​

Phosphate-based alkaline cleaners (Grainfather High Performance Cleaner) — A​

Five Star PBW — A*​

Compatibility — beer/wort: A​

Beer at fermentation and storage conditions​

Sour beer​

Wort — temperature governs​

Oxygen ingress​

UV transparency and skunking​

Oxebar — barrier PET as a packaging solution​

PET vs PP and HDPE as fermentation vessels​

Barrier PET — Oxebar construction and cleaning​

Construction​

Chemical compatibility​

The additional constraint for Oxebar​

ESC and pressure — structural failure risk​

PET in homebrewing — the practical picture​

Assessing and retiring equipment​

Summary by article type — scenarios​

Summary by article type​

Footnotes​