How to Sterilise Glass Jars and Bottles: The Complete UK Guide

Whether you need to sterilise glass jars and bottles depends on what goes in them, not on the glass. If your product has no preservative, you almost certainly need to sterilise, because your process determines the shelf life. If it's preserved, say with high alcohol content, thorough cleaning may be enough, but only if you've tested it. 

For glass, dry heat works best: 160°C for two hours, 170°C for one hour, or 180°C for 30 minutes, according to CDC sterilising guide and European Pharmacopoeia preparation of sterilise products. This guide is for people filling jars and bottles with products they sell, and covers when to sterilise, each method, and how to test.

 

Quick Answer: Wash your jars and bottles, put them in a cold oven, and heat to 160°C for 2 hours, 170°C for 1 hour, or 180°C for 30 minutes. Let them cool inside the oven. Lids, pipettes and bulbs never go in the oven: each needs its own method. Boiling or a dishwasher will clean jars, but won't fully sterilise them.

 

In this guide:

• Do you need to sterilise, or is cleaning enough?

• Sanitising vs sterilising

• Methods compared

• How to sterilise jars in the oven

• Steam sterilisation and boiling

• Chemical methods and UV

• Pipettes, bulbs, caps and liners

• How to prove your process works

• FAQ

 

 

Do you need to sterilise, or is cleaning enough?

This is the question people get stuck on. The better question is: if you don't sterilise, does your product go off?

It comes down to what's in it. Some products contain natural antifungals, antibacterials, or preservatives that keep the microbial load down and help them last. Others contain biologically active compounds that enzymes can break down over time.

Our rule of thumb: if there's no preservative at all in your product, you're likely to need to sterilise, because your cleanliness during production is what sets the shelf life. If you do have a preservative, whether that's alcohol or something else, sterilising matters less, because the preservative is doing that job. Whether a preservative actually works in your formula is something you can test formally, with a preservative efficacy or "challenge" test as mentioned in International Organization of Standardization for antimicrobial protection of cosmetic products.

Either way, check your shelf-life claim. If you tell customers your product lasts two years, have you proven it? As strictly mentioned in GOV UK guidance on selling cosmetics in the UK, your product's safety assessment has to cover its stability and microbiological quality, so this isn't optional. We cover how to test at the end.

Why time and temperature matter: sanitising vs sterilising

Not all microbes are equally easy to kill. Most bacteria, yeasts and moulds in their active ("vegetative") form die quickly at temperatures well below boiling. As stated by CDC in their sterilising guide, bacterial spores are different: they're a dormant, heavily protected form that can survive boiling water and moderate oven heat.

That's the difference between two words that often get used interchangeably:

• Sanitising cuts the microbial load right down, killing most active microbes. Boiling, a hot dishwasher cycle, and most chemical rinses do this.

• Sterilising kills everything, spores included. That needs either dry heat at 160–180°C held for long enough or pressurised steam at 121°C or above, as in an autoclave or pressure cooker supported by CDC sterilising guide and European Pharmacopoeia preparation of sterilise products.

Dry heat needs higher temperatures and longer times than steam, because hot, dry air transfers heat into microbes far less efficiently than moist steam does. For reference, pharmaceutical manufacturers go even further, heating glass to around 250°C to destroy pyrogens (fever-causing bacterial residues), not just living microbes.

For many preserved products, sanitising is enough. For unpreserved products, aim for true sterilisation.

Method Compared

There’s no single perfect method, so match the method to each part supported by CDC in Guideline for Disinfection and Sterilization in Healthcare Facilities (2008) and USDA National Center for Home Food Preservation, guidance on sterilising jars and lids.

How to sterilise jars in the oven

Dry heat works for jars and glass bottles alike. It's how manufacturers sterilise glass in large quantities, and it's the method we lean on most.

1. Clean first. Wash and rinse your bottles as described in our cleaning guide. Heat deals with microbes, not residue.

2. Separate the closures. Take off all caps, lids, pipettes and liners. They each need their own method, covered below.

3. Heat slowly. Put the glass into a cold oven and bring it up to temperature gradually.

4. Hold at temperature. Once the glass itself is at temperature, hold it at 160°C for 2 hours, 170°C for 1 hour, or 180°C for 30 minutes. Use an oven thermometer: domestic oven dials can be off by 10–20°C.

5. Cool inside the oven. Turn the oven off and let the glass cool slowly with the door closed. Sudden temperature changes are what crack glass. Standard soda-lime containers are typically tested to withstand a difference of only around 42°C mentioned in BS EN in thermal shock resistance of glass containers. Don't put hot glass onto a cold or wet worktop, and don't pour cold product into hot glass or hot product into cold glass.

6. Handle and fill. Use clean oven gloves, hold bottles from the outside, and keep your fingers off the rims and the inside. Fill once the glass is at the temperature your product needs, and cap it straight away.

Steam sterilisation

Steam under pressure sterilises faster than dry heat and at a lower temperature. A pressure steriliser at 120°C for 20 minutes counts as sterilising. For reference, the CDC's standard cycle is 121°C for at least 15 minutes. An autoclave or a pressure cooker can reach either. It's a good option for glass pipettes, natural rubber bulbs, and any parts that can't take oven temperatures but can take steam.

Put a strip of autoclave indicator tape on each load. It changes colour once the cycle has reached temperature, so you can see at a glance that it worked.

Household “steam sterilisers” sold for baby bottles are a different thing. They run at around 100°C at normal pressure, which leaves you with a low bacterial load, not a sterile one. That’s fine for preserved products, but if your product has no preservatives, it isn’t enough. For that, you need steam at 120°C under pressure for 20 minutes, with indicator tape to show it worked.

Boiling glass bottles in a pot

Boiling is quick and needs no special equipment, but it sanitises rather than sterilises, because some bacterial spores survive 100°C. It's fine for preserved products or as a step before filling with a hot product. Guidance for home preserving uses a 10-minute boil for jars.

• Clean first. Wash your bottles as described in our cleaning guide.

• Boil. Place the glass bottles (not the droppers) in a large pot, fully submerged, and boil for 10–15 minutes. Put them in cold water and bring them up together to avoid thermal shock.

• Remove carefully. Lift the bottles out with sterilised tongs and stand them upside down on a clean rack or lint-free cloth to drain and dry.

Chemical method: Milton, sodium metabisulfite and alcohol

If heat isn't practical, chemical methods will sanitise or disinfect. None of them reliably kill every spore, so treat them as a step below heat.

• Milton: The liquid is a dilute sodium hypochlorite (chlorine) solution, and the tablets release chlorine from sodium dichloroisocyanurate. Use the dilution and soak time on the pack. It's the same product the NHS suggests for sterilising baby feeding equipment.

• Sodium metabisulfite: When in water it releases sulphur dioxide, which is what does the antimicrobial work. It's the standard sanitiser in home winemaking as tested by Roland Jackson in Wine Science.

• Alcohol: A 70% solution works better than 100%. Alcohol kills microbes by denaturing their proteins, and that needs water present. Pure alcohol also evaporates before it has time to work. The effective range is about 60–90%.

If you sanitise with Milton or metabisulfite, rinse afterwards with sterile water: cooled boiled water, distilled water, or water that's been through a purifier. Tap water is safe to drink, but it isn't sterile, so rinsing with it puts microbes straight back in, just as WHO writes in Guidelines for Drinking Water Quality.

Sterilising with UV

CDC in their sterilising guide reminds us that UV-C light damages microbes' DNA, but only on surfaces it directly reaches. Threads, crevices, and anything behind amber glass get missed, and too much exposure can degrade rubber bulbs over time. That's why we lean on dry heat for glass and steam for pipettes instead.

Sterilising dropper pipettes, bulbs, caps, and liners.

Take every closure apart first, so each material gets the method it can handle. Where a part can’t take heat, 70% alcohol is the standard choice, and it’s what NHS infection control guidance uses for disinfecting equipment. It disinfects rather than sterilises, so treat it as a step below steam.

• Pipettes: separate them from the bulbs. They can go through steam sterilisation, or in the oven alongside your bottles. If you can’t use heat, soak them in 70% alcohol or a sanitising solution such as Milton for 10 minutes, then rinse with sterile water.

• Natural rubber bulbs: they survive steam sterilising at 120°C well. Never put them in the oven, which melts them. If you don't have steam, wipe them inside and out with 70% alcohol and leave to dry.

• LDPE dripper inserts and PP caps: check before you commit. Steam can deform some plastics, so run a few through your own equipment first. Afterwards, the insert should still fit snugly in the bottle, and the cap should screw down tight with no warping. If not, that equipment isn't right for them.

• EPE-lined lids: EPE (expanded polyethylene) is the foam wad inside the cap that presses against the rim to seal the bottle. Give it a light spray of 70% alcohol and leave it to air dry somewhere flies, bugs and pets can’t reach. No rinse needed.

Lay all components on a clean, lint-free cloth and let them dry completely before you reassemble them.

How to prove your process works

Sterilising once doesn't prove your process works. Testing does. Keep three to five samples from each batch, store some warm (30–35°C) and some at room temperature, and check them monthly for six months as already covered by European Pharmacopoeia in sterilising tests. Look for bubbles, mould, or changes in colour, smell or texture.

Record the details of every batch, because ingredients vary: one batch of herbs might be clean, the next might carry mould because it was picked damp.

Frequently Asked Questions

How long to sterilise jars in the oven, and at what temperature?

Heat the oven slowly, then hold the glass at 160°C for 2 hours, 170°C for 1 hour, or 180°C for 30 minutes. The 120–140°C often quoted online will sanitise but can leave bacterial spores alive. Only the glass goes in; see the next question for lids.

Can you sterilise jars in the dishwasher?

A dishwasher will clean jars well, but don't rely on one to sterilise them. A kitchen dishwasher isn't a clean environment, especially if the filters haven't been cleaned recently, and it runs on tap water, which isn't sterile. It still reduces the bacterial load. Check your tablet leaves no residue, and if your product has no preservative, follow up with the oven for the glass and steam for the pipettes.

Do jars and bottles from a supplier come sterilised?

Not ours, and it's worth checking with anyone you buy from. Glass is sterile when it's made, but transit, warehousing, and cardboard boxes can bring in bacteria or mould afterwards. We supply glass we believe to be clean at the point of wrapping: clean and rinsed, not sterile. Proving sterility needs agar-plate testing under strict rules, so if your product needs sterile glass, sterilise it yourself.

Do I need to sterilise bottles for a tincture?

Probably not, if it has a high alcohol content, because the alcohol is likely to suppress bacteria on its own. Your herbs or mushrooms can still carry mould if they were picked or dried badly, and one clean batch doesn't guarantee the next. Test your process: keep three to five samples of each batch at around 35–37°C and check them over six months.

Can I rinse sterilised bottles with tap water?

No. Tap water isn't sterile, so rinsing with it puts contamination straight back in. It's the same reason I wouldn't count a dishwasher as sterilising. After Milton or sodium metabisulfite, rinse with distilled water or water that's been through a purifier. EPE-lined lids don't need rinsing: a light spray of 70% alcohol, left to air dry somewhere flies, bugs and pets can't reach, is enough.

Conclusion

Sterilising isn't a box to tick. It's one part of making sure your product is still what you said it was on the day someone uses it. Match the method to each part, then test that it works.

Once your bottles are sterilised, the next question is how to look after them, and whether you can safely reuse them. We get it covered for the right way of looking after sterilised glass bottles using any kind of method. You can check out the right way of Cleaning and reusing glass dropper bottles.