EditorPotassium Sorbate CAS 24634-61-5: Uses, Typical Dosage and Storage
Potassium sorbate sits in a slightly awkward position among food preservatives. It is effective against mould and yeast, ineffective against most bacteria, and only works well in a fairly narrow pH range. Get those three facts wrong and it looks like a weak preservative. Get them right and it does its job at a few hundred parts per million.
What it is
Potassium sorbate is the potassium salt of sorbic acid. The CAS number is 24634-61-5, molecular formula C6H7KO2, molecular weight 150.22 g/mol. It appears as a white to off-white granular powder or as pellets, with a mild characteristic odour and good solubility in water.
The salt form is used far more often than sorbic acid itself. Sorbic acid dissolves poorly in water and is only practical in acidic liquid systems. Converting it to the potassium salt raises water solubility to roughly 1400 g/L at 20°C, which makes it workable in beverages, sauces and brines.
In dry form it is stable. In solution it is not, which is the source of most processing problems.
How it works
The active form is the undissociated sorbic acid molecule, not the sorbate ion. That distinction drives everything about how the product should be used.
At pH 5, a meaningful share of the preservative is present in the undissociated form and antimicrobial activity is strong. At pH 6.5, that share drops sharply and the same dose does much less. Above pH 7 the practical effect against mould is negligible.
| pH | Share of undissociated acid | Practical antimicrobial activity |
|---|---|---|
| 4.0 | High | Strong |
| 5.0 | Moderate to high | Effective at typical doses |
| 6.0 | Low | Marginal, dose must rise sharply |
| 7.0 | Very low | Not usable against mould |
This is why potassium sorbate is used mainly in acidic foods: soft drinks, fruit juices, jams, pickles, cheese, baked goods with fruit fillings, wine and dried fruit. In neutral or alkaline products it is the wrong tool, and no increase in dose will fix that.
It also explains the combination with benzoates. In very acidic systems the two cover slightly different pH bands, and blends are common in beverage applications.
Typical use levels
Dosage depends on the product, the target organism and the shelf life required. As a general frame:
Soft drinks and juices: 200 to 500 mg/L, calculated as sorbic acid
Sauces, dressings and pickles: 500 to 1000 mg/kg
Cheese and dairy analogues: surface treatment or in-mass, typically 1000 mg/kg maximum in many jurisdictions
Baked goods with fruit fillings: 500 to 1000 mg/kg
Dried fruit: up to 1000 mg/kg in many markets
Regulatory limits differ by market. The EU lays out permitted levels in Regulation (EC) No 1333/2008 and its amendments, the US framework sits in 21 CFR 182.3640, and most importing countries publish their own limits under a national food additive standard. Confirm the destination market's limit before fixing a formulation, since a level accepted in one market can exceed the ceiling in another.
Two practical notes on dosing. First, limits are usually expressed as sorbic acid, so the potassium sorbate quantity is about 1.34 times the sorbic acid figure. Second, adding the preservative late in processing, after the product has cooled, reduces losses and gives better control.
Stability and storage
Solid potassium sorbate keeps well. Store it sealed, away from moisture, at ambient temperature, and it holds for around two years. It is not light sensitive in the way some actives are.
The powder absorbs moisture and cakes if the bag is left open, which is not a safety problem but does make dosing inaccurate. Keep the liner closed and use opened bags within a reasonable period.
In solution, three things degrade it: prolonged heat, light, and contact with metal ions. Iron and copper accelerate oxidation and cause browning in some products. Where a stock solution is used, prepare it in stainless steel or plastic, keep it out of direct light, and use it within a day or two.
One more behaviour worth knowing: sorbate can be broken down by certain spoilage microorganisms into trans-1,3-pentadiene, which carries a kerosene-like odour. It is a sign that the preservative itself has been consumed by microbial activity rather than that the material was defective on arrival.
Quality parameters to check
For incoming inspection, the useful checks are assay, loss on drying, and heavy metals. Food-grade material typically specifies assay of 98.0 to 101.0 percent on the dried basis, loss on drying not above 1.0 percent, and heavy metals within the limits of the relevant monograph.
Shelf-life and organoleptic complaints in finished products usually trace back to pH and dosing, not to the incoming material. Checking the specification sheet is worthwhile, but checking the product pH is where the money is.
Potassium sorbate is one item in the food additives range. Where a formulation also needs an antioxidant or a colour component, plant-derived material such as grape seed extract or lutein powder is often specified alongside it, and the same pH and storage discipline applies to both.
For products where the flavour profile is the constraint rather than the preservation, the essential oils and spices range covers the usual bases. If you are working on a formulation and want the technical data sheet or a sample specification for review, send us the intended application and target market.
