Sanitisation
Contamination is the most common cause of ruined batches. A wild yeast, an unwanted bacterium, or a stray acetobacter can turn months of careful work into vinegar. The good news: contamination is almost entirely preventable. Thorough sanitisation of everything that touches your must is the single most important habit in meadmaking.
Why sanitisation matters
There is an important distinction between cleaning and sanitising, and both are necessary:
Cleaning
Removes visible dirt, residue, and organic matter using soap, hot water, and physical scrubbing. Cleaning does not kill microorganisms: it removes the material they live in.
Sanitising
Kills or inhibits microorganisms on a surface that has already been cleaned. Sanitiser cannot work effectively on a dirty surface: organic matter physically protects bacteria from contact with the sanitising agent.
The rule is absolute: clean first, sanitise second, always.
Without proper sanitisation, any of the following can take hold in your must:
- Acetic acid bacteria (acetobacter): produces acetic acid, the primary component of vinegar. The most feared contamination in mead.
- Wild yeast: unpredictable fermentation behaviour, harsh off-flavours, potential to outcompete your cultured strain.
- Lactic acid bacteria: can produce sourness and ropiness (a viscous, rope-like texture caused by polysaccharide production).
- Mould: visible contamination on must surfaces, potential mycotoxins, and off-flavours that penetrate the liquid.
Types of sanitiser
Several sanitisers are used in homebrewing. They vary in convenience, effectiveness, and whether rinsing is required after contact.
Star San
Phosphoric acid based, recommended
The most widely used no-rinse sanitiser in homebrewing. Mix at 1 ml per litre of water (1 oz per 5 US gallons). The foam it produces is harmless ("don't fear the foam" is the mantra).
Contact time: 30 seconds is sufficient. No rinse needed. Highly effective, easy to use, and safe for all equipment. Breaks down to phosphoric acid and water, a benign residue that will not harm your mead or yeast.
Shelf life of the diluted solution is 2–4 weeks. Check pH with a strip; discard and make a fresh batch when pH rises above 3.
Potassium metabisulphite (campden / K-meta)
Sulphite based, rinse required
A sulphite-based sanitiser common in winemaking and meadmaking. Dissolve 1 campden tablet per 4 litres of water, or use powdered K-meta at 1 g per litre.
Must be rinsed after contact: K-meta leaves a sulphite residue that can inhibit or kill yeast if not removed. Has a strong sulphur smell. Effective but more cumbersome than no-rinse options.
Also used post-fermentation to halt fermentation and prevent oxidation, and to pre-treat must before pitching a cultured yeast strain.
Sodium metabisulphite
Sulphite based, rinse required
Similar in use and effectiveness to potassium metabisulphite but sodium-based. Same usage and rinsing requirements. Avoid if you are preparing mead for anyone on a low-sodium diet.
Iodophor
Iodine based, no-rinse at low concentration
Another no-rinse option at the correct dilution (12.5 ppm iodine). Can stain equipment and skin amber. Effective but less popular than Star San for meadmaking.
If used at a higher concentration than specified, rinsing is required. Follow the manufacturer's instructions for the specific product.
Bleach (sodium hypochlorite)
Not recommended for regular use
Cheap and widely available, but requires extremely thorough rinsing: any residue will kill your yeast and leave pronounced off-flavours. Chlorine compounds can react with phenols in your must to produce TCA, a medicinal, antiseptic off-flavour.
Not recommended for regular meadmaking use. Stick to purpose-made brewing sanitisers.
Heat sanitisation
Boiling water or steam
Boiling water or pressurised steam can sanitise equipment that can tolerate it: stainless steel, glass, silicone. Not practical for most plastic equipment, large vessels, or anything with tight seals.
Useful for boiling small items (spoons, funnels) if you have no chemical sanitiser to hand, but chemical sanitisation is more practical for routine brew-day use.
No-rinse sanitisers explained
At the correct dilution, Star San and similar no-rinse sanitisers leave so little residue on equipment surfaces that it is genuinely harmless, both to your fermentation and to you. The acid breaks down quickly once exposed to the mineral content of your must, and the quantities involved are far too small to measurably affect pH or yeast health.
A small amount of Star San solution draining from a sanitised vessel or funnel into your fermenter will not harm your mead. You do not need to shake it dry or wipe it down; in fact, doing so defeats the purpose.
Do not rinse after sanitising with a no-rinse sanitiser.
Tap water is not sterile. Rinsing with tap water reintroduces microorganisms to a surface you have just sanitised. Let it drain: do not rinse.
Technique and tips
Spray bottle at the bench
Keep a small trigger spray bottle filled with diluted Star San at your bench during brew day. Spray anything that will touch your must: your hands, the outside of lids, airlocks, the rim of vessels, the tip of your wine thief. A spray bottle makes this fast enough to become automatic. Label it clearly.
The two-vessel method
Fill your fermenter with sanitiser solution, swirl to coat all internal surfaces, then drain into a second vessel (a bucket works well). Use the drained solution to sanitise smaller items: hydrometers, wine thieves, funnels, spoons, tubing. Work through your equipment systematically before you begin.
Siphon tubing and hoses
Draw sanitiser solution through your siphon tube and racking cane to sanitise the interior surfaces. The outside is easy; the inside requires flow. Let it drain fully before use: you want it wet, not pooled.
Airlocks
Fill airlocks with Star San solution rather than plain water. If liquid is ever sucked back into the fermenter during a temperature drop or pressure change, Star San solution is far safer than unsterile water.
Timing
Sanitise as close to use as possible. Equipment left to dry after sanitising is no longer protected: microorganisms from the air will settle on dry surfaces within minutes. Work with wet, dripping equipment. If something dries before you use it, re-sanitise.
Your hands
Your hands carry bacteria and wild yeast. Wash thoroughly with soap and rinse well, then spray with Star San solution before handling sanitised equipment or reaching into vessels. This is especially important when taking gravity readings, adding nutrients, or degassing.
Storing sanitiser solution
Star San diluted solution keeps for 2–4 weeks in a sealed container if made with low-mineral water. Hard tap water shortens shelf life: the minerals neutralise the phosphoric acid faster, raising the pH and reducing effectiveness. Using filtered or bottled water gives a longer-lasting solution.
Check with a pH strip before each use. Star San solution should be below pH 3 to remain effective. When it rises above 3, discard it and make a fresh batch. A 500 ml bottle of Star San concentrate makes a very large volume of working solution, and it is not worth compromising a batch to avoid throwing away a litre of spent solution.
Store in a labelled, sealed container (a repurposed plastic jug or the spray bottle itself). Keep out of reach of children. Never store sanitiser solution in a food or drink container.
Common mistakes
- Sanitising without cleaning first. Organic residue physically shields microorganisms from the sanitising agent. Clean, then sanitise, every time.
- Rinsing after sanitising. Tap water is not sterile. Rinsing with it reintroduces contamination to a surface you just sanitised. Drain, don't rinse.
- Not sanitising the outside of lids and bungs. Anything that contacts the opening of your fermenter counts: the outside of a lid, the thread of a bung, the rim of a vessel.
- Using too weak a solution. Follow dilution ratios exactly. Below the minimum effective concentration, the sanitiser does not reliably kill microorganisms.
- Using too strong a solution. Above the recommended concentration, you waste product and risk leaving flavour-affecting residue, and for products that require rinsing, the rinse becomes more critical.
- Forgetting the hydrometer and wine thief. These go directly into your must every time you take a reading. They must be sanitised every single use.
- Reusing spent sanitiser solution. Check pH before relying on stored solution. A cloudy, flat-smelling solution that no longer foams is a sign the acid has been neutralised: make a fresh batch.