Why Does Food Grade Silicone Tubing Turn Yellow Over Time and How Do You Prevent It?

This is the question most people want answered before anything else, so let's address it directly.

The answer depends on the cause of the yellowing. In the most common scenario - yellowing caused by the oxidation of peroxide-curing residuals in the silicone compound over time - the colour change is primarily cosmetic. The underlying silicone polymer remains chemically stable and food-contact compliant. The yellowed tubing is not leaching additional compounds into your product as a result of the colour change itself; the discolouration is a surface and bulk optical effect, not an indicator of chemical breakdown of the polymer.

However, yellowing can also indicate more serious issues - such as thermal degradation from operating above the tubing's rated temperature, or chemical attack from incompatible cleaning agents. In these cases, the colour change is a symptom of actual material degradation that affects mechanical properties and may compromise food safety.

The practical rule: yellowing alone, in the absence of other signs (softening, tackiness, cracking, brittleness, odour change, visible surface damage), is generally cosmetic. Yellowing combined with any of those other signs indicates degradation that warrants immediate replacement.

Understanding what's actually causing the colour change is the only way to address it at the root. Here are the five most common causes, in order of how frequently they occur in food applications.

1. Peroxide Curing Residuals Oxidising Over Time

This is by far the most common cause of yellowing in food grade silicone tubing, and it's entirely a function of manufacturing choice rather than user error.

Silicone rubber can be cured (cross-linked) by two main methods: addition curing using a platinum catalyst, or condensation/peroxide curing using organic peroxides. Peroxide curing is less expensive and is widely used in general-purpose silicone products. However, peroxide curing leaves residual peroxide decomposition products in the cured silicone - primarily benzoic acid compounds and other oxidative byproducts from the curing reaction.

Over time, particularly with heat exposure and oxygen contact, these residuals oxidise and produce chromophores - chemical structures that absorb visible light and appear as yellow or brownish colouration. This oxidation process is gradual, which is why yellowing typically appears after months of use rather than immediately.

The key point: this yellowing is intrinsic to peroxide-cured silicone and cannot be fully prevented through user care. The solution is to specify platinum-cured silicone from the outset.

2. Prolonged Heat Exposure Above Rated Temperature

Silicone's thermal stability has genuine upper limits. Standard food safe silicone tubing is rated for continuous service to approximately 200–230°C depending on the compound. When tubing is consistently operated above its rated temperature - or even close to the upper limit for extended periods - thermal oxidation of the silicone polymer itself begins to occur.

Thermal oxidation produces yellow and eventually brownish discolouration that starts at the outer surface and progressively penetrates the bulk. Unlike peroxide residual yellowing, thermally induced discolouration is accompanied by hardening and loss of elasticity. The tubing becomes progressively less flexible and eventually brittle.

In food processing applications, the most common scenario for thermal yellowing is tubing installed too close to heat sources - steam pipes, hot equipment surfaces, or process lines where insulation is inadequate. Tubing routing that brings silicone into contact with surfaces above 200°C will cause thermal degradation.

3. Certain Cleaning Chemical Reactions

Not all cleaning chemicals are compatible with silicone, and some react in ways that produce visible discolouration.

The most commonly encountered culprit is iodine-based sanitisers (iodophors). Iodine is a known staining agent for silicone - it absorbs into the surface layer and produces a yellow-brown discolouration that is extremely difficult to remove once established. This reaction doesn't necessarily indicate chemical degradation of the silicone polymer itself, but the iodine-stained surface may retain iodine residuals that could affect product taste.

High-concentration sodium hypochlorite (bleach) at elevated temperatures can also produce oxidative yellowing of silicone surfaces. Standard CIP concentrations of sodium hypochlorite (200–400 ppm available chlorine) at ambient temperature are generally well-tolerated by food grade silicone. It's the combination of high concentration (above 1,000 ppm), elevated temperature (above 50°C), and extended contact time that causes problems.

Quaternary ammonium compounds (quats) at high concentrations can cause surface swelling and discolouration in some silicone compounds, though this is less common than iodophor or hypochlorite staining.

4. Oil and Fat Absorption at Elevated Temperatures

As discussed in the context of food oil applications, silicone shows low but non-zero absorption of edible oils and fats, particularly at elevated temperatures. In applications involving extended contact with hot cooking oils, rendered animal fats, or high-fat dairy products at elevated temperatures, absorbed lipids can undergo oxidation within the silicone matrix over time - producing yellow discolouration that originates from within the material rather than from the silicone polymer itself.

This type of yellowing is more common in high-fat applications at elevated temperatures and is more prevalent in peroxide-cured silicone (which has a more open polymer network that facilitates lipid absorption) than in platinum-cured products.

5. UV Exposure in Outdoor or Well-Lit Installations

Prolonged direct UV exposure - in outdoor installations, near UV sterilisation equipment, or in facilities with intense lighting at specific wavelengths - can cause surface yellowing in silicone. As discussed in the context of silicone's UV resistance, the Si-O backbone is intrinsically resistant to UV-induced chain scission, but very long exposure periods cause slow photodegradation of surface silicone oligomers that produces a chalky or slightly yellowed appearance.

UV-induced yellowing is usually limited to the outer surface and is the least concerning of the five causes from a food safety perspective.

The single most effective thing you can do to prevent yellowing in food grade silicone tubing is to specify platinum-cured (addition-cured) products. Here's why the chemistry makes such a difference.

In platinum-cured silicone, the cross-linking reaction involves a platinum catalyst that facilitates the addition reaction between vinyl-functional and Si-H functional silicone polymers. The platinum catalyst is consumed cleanly in the reaction and becomes part of the cross-linked network. There are no residual peroxide decomposition products, no organic byproducts, and no compounds present in the cured material that would undergo oxidative yellowing over time.

The result: platinum-cured silicone maintains its original translucent or clear appearance significantly longer than peroxide-cured equivalents under equivalent service conditions. A 2020 study published in Polymer Degradation and Stability compared the discolouration behaviour of platinum-cured and peroxide-cured food-grade silicone compounds after accelerated thermal ageing at 150°C for 500 hours. The platinum-cured samples showed a yellowness index (ASTM E313) increase of 3.2 units - within the range of barely perceptible colour change. The peroxide-cured samples showed a yellowness index increase of 18.7 units - clearly visible yellowing.

This is a meaningful real-world difference. In commercial food operations, the visual appearance of contact materials matters for hygiene audits, retailer inspections, and quality assurance documentation. Platinum-cured food safe silicone tubing from a reputable manufacturer maintains a cleaner appearance throughout its service life.

If your silicone tubing is yellowing rapidly - within weeks rather than months - cleaning chemistry is the most likely cause. Here's what to check and what to use instead.

Iodophor sanitisers: Replace with peracetic acid (PAA) or hydrogen peroxide-based sanitisers, which are fully compatible with food grade silicone and do not cause staining. PAA at use concentrations (100–200 ppm) and temperatures (up to 40°C for most formulations) is the industry standard for silicone-compatible sanitation in food and beverage operations.

High-concentration hypochlorite: Reduce concentration to below 200 ppm available chlorine, or switch to alternative sanitisers. If hypochlorite must be used at higher concentrations, limit contact time and temperature. A brief rinse exposure is very different from extended soak-type cleaning.

Caustic CIP (NaOH): Standard food-industry CIP concentrations (1–2% NaOH at 70–80°C) are compatible with food grade silicone and do not cause yellowing. Problems arise when concentration or temperature significantly exceeds these norms. Verify your CIP parameters against the tubing manufacturer's recommendations.

Acid CIP (nitric acid, phosphoric acid): Similarly, standard CIP concentrations (0.5–1.5% nitric acid or 1–2% phosphoric acid at 65–75°C) are compatible with silicone. Issues arise with concentrated acid solutions or extremely extended contact times.

A useful resource: the European Hygienic Engineering & Design Group (EHEDG) publishes guidance on cleaning chemical compatibility with food contact materials, including silicone. This guidance aligns CIP chemical type, concentration, and temperature against material compatibility ratings and is a practical reference for CIP protocol design.

A craft beverage manufacturer in Southeast Asia noticed significant yellowing of silicone transfer tubing approximately four months after installation across their syrup mixing and filling lines. The tubing had been purchased from a regional distributor at a competitive price point; the product was labelled "food grade" but no certification documentation had been supplied.

Sunhingstones was contacted by the facility's quality manager after the yellowing triggered a question from an external food safety auditor during a routine inspection. The auditor had noted the discolouration in the facility's hygiene records and requested evidence that the tubing remained food-safe.

Investigation findings:

The installed tubing was peroxide-cured - confirmed by a standard acetone extraction test, which produced a characteristic odour from peroxide residuals not present in platinum-cured products.

The facility's sanitisation protocol included weekly iodophor treatment, which had accelerated the surface yellowing significantly.

Operating temperatures on the syrup mixing lines reached 85°C, above the thermal comfort zone for peroxide-cured silicone.

Sunhingstones supplied replacement food safe silicone tubing - platinum-cured, with LFGB certification documentation - across all affected line sections. The sanitisation protocol was revised to replace iodophor with peracetic acid at 150 ppm.

At the six-month review after replacement, no visible yellowing had occurred across any of the new tubing sections. The quality manager confirmed that the external auditor's concern had been formally closed following provision of the new tubing's certification documentation.

Specify platinum-cured silicone from the start. This is the single most effective prevention. Ask any supplier explicitly whether their product is platinum-cured and request written confirmation in the product data sheet.

Avoid iodophor sanitisers. Switch to peracetic acid or hydrogen peroxide-based alternatives that are fully compatible with silicone and do not cause staining.

Keep operating temperatures within the rated range. For standard food grade silicone, continuous service above 180°C accelerates thermal yellowing. Check the product's rated temperature against your actual maximum operating condition and verify there's adequate margin.

Check CIP chemical concentrations. High-concentration hypochlorite and very high-temperature caustic CIP can cause accelerated discolouration. Verify your CIP parameters are within standard food industry ranges.

Protect outdoor installations from direct UV. If tubing is installed in a well-lit or outdoor position, UV-protective conduit or sheathing prevents the slow surface yellowing that prolonged UV exposure causes.

Request migration and safety documentation from your supplier. A reputable food safe silicone tubing manufacturer can provide data on how their product behaves after extended service, including discolouration and migration change data. This documentation is useful for food safety audit responses.

Inspect regularly and track colour change over time. Photographing tubing at installation provides a baseline for comparison at periodic inspection intervals. Gradual yellowing over 18–24 months is different from rapid yellowing over weeks; the rate of change tells you more than the colour alone.

The colour of silicone tubing alone is not a sufficient reason to replace it. Use these criteria:

Monitor but don't replace yet:

Mild yellowing after 12–24 months of service, platinum-cured product, no other signs of degradation

Tubing remains flexible and returns to original shape after handling

No detectable odour change

Certified product with documentation confirming food-contact compliance

Plan for near-term replacement:

Moderate yellowing in peroxide-cured product, particularly in fat-contact or high-temperature applications

Yellowing accompanied by slightly increased stiffness

Replace immediately:

Yellowing combined with surface tackiness, softening, or cracking

Yellow-brown discolouration with noticeable hardening or brittleness

Any detectable odour or taste transfer to the product

Visible surface damage, delamination, or blistering

Yellowing in food grade silicone tubing is a manageable problem with a clear solution hierarchy: start with platinum-cured products, manage cleaning chemistry carefully, and operate within the tubing's rated temperature range. Do all three, and yellowing over a normal service life is either absent or cosmetically minor.

At Sunhingstones, we manufacture food safe silicone tubing and food grade reinforced silicone tubing in platinum-cured formulations, with LFGB, FDA 21 CFR, and NSF 51 certification. Discolouration resistance is documented in our product ageing test reports, available on request.

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1.ASTM E313 – Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates. ASTM International. https://www.astm.org/
2.FDA 21 CFR 177.2600 – Rubber articles intended for repeated use. U.S. Food and Drug Administration. https://www.ecfr.gov/
3.LFGB (Lebensmittel- und Futtermittelgesetzbuch) § 31 – Food contact material requirements. https://www.gesetze-im-internet.de/lfgb/
4.NSF/ANSI 51 – Food Equipment Materials. NSF International. https://www.nsf.org/
5.European Hygienic Engineering & Design Group (EHEDG) – CIP Chemical Compatibility with Food Contact Elastomers. Technical Guideline. https://www.ehedg.org/