Food-Grade Potassium Hydroxide: FSSC 22000, E525 and What Buyers Should Verify

“Food-grade potassium hydroxide” is not a statement about purity – industrial KOH can be 90% and food-grade KOH can be 85%. The difference is the impurity profile, the documentation, and the management system behind the plant that made it. This article sets out what actually changes when you buy food-grade KOH, what FSSC 22000 certifies, and the two specification lines that catch buyers out: carbonate content and mercury.

1. What “food grade” changes – and what it does not

Dimension	Industrial grade	Food grade
Assay	Often higher (90-92% flake is common)	Often lower – 85.0-100.5% is a normal food-grade range because the material is sold on total alkali and may contain water and carbonate
Heavy metals	May not be specified individually	Specified: As, Pb, Hg and total heavy metals as Pb, each with its own limit
Documentation	COA and SDS	COA, SDS, specification, and a food-safety management system certificate
Management system	Quality system, if any	Certified food-safety system (FSSC 22000 or equivalent GFSI-recognised scheme), audit trail, traceability, allergen and hygiene controls
Sourcing visibility	Limited	The certificate names the site; the buyer can audit against it

So the question to ask is not “how pure is it” but “what is the impurity profile, and can you show me the system that produced it”. A 90% industrial flake and an 85% food-grade flake can both be excellent products; only one of them can go into a food line.

2. FSSC 22000: what the certificate actually covers

FSSC 22000 is a food-safety management system certification recognised by the Global Food Safety Initiative. It is built from three parts, and understanding the structure tells you what the certificate does and does not assure:

Component	What it covers	What it does not cover
ISO 22000	The management system: hazard analysis, HACCP principles, verification, traceability, recall	Product fitness for a specific application
Sector prerequisite programmes (ISO/TS 22002-1 for manufacturing)	Hygiene, pest control, maintenance, personnel, cleaning, foreign-body control	Chemical specification – that is still the COA’s job
FSSC additional requirements	Service and purchased-material management, product labelling, food defence, allergen control	Regulatory compliance in your destination market

For a buyer the practical value is threefold. First, it is evidence that the site is audited by a third party against a recognised standard. Second, it requires traceability and a recall procedure, which is what you actually need if something goes wrong. Third, it is increasingly a precondition for supplying food manufacturers at all – many purchasing departments will not open a supplier file without a GFSI-recognised certificate. But it is not a substitute for the specification: a certified system can still produce material outside your impurity limits if your limits are tighter than theirs.

3. E525: what potassium hydroxide does in food

Potassium hydroxide carries the food additive number E525 and functions as an acidity regulator. Its uses are unglamorous and essential:

Application	Role	Why grade matters
Cocoa alkalisation (“Dutching”)	Raises pH, darkens colour, modifies flavour	High dose relative to the finished product, so trace metals matter
Starch modification	Swelling and gelatinisation control	Clarity of solution is a functional requirement, not cosmetics
Edible oil refining	Neutralises free fatty acids	Soapstock and metal residues carry through to the oil
pH adjustment	General acidity regulator in beverages and processes	Carbonate content changes the effective alkalinity
Saponification of food-grade fats	Produces food-grade soaps and emulsifiers	Impurity profile carries directly into the product

As with all additives, the permission is tied to the use and the market, not to the substance in general. A food-grade certificate tells you the material is suitable for food use; it does not tell you that your specific application is permitted in your specific country.

4. Reading the specification: two lines that matter most

Item	Typical food-grade limit	What it tells you
KOH content	85.0 – 100.5%	Total alkali expressed as KOH. The wide range reflects that flake carries water and some carbonate
K₂CO₃	2% max	The freshness indicator. Potassium carbonate forms when KOH absorbs atmospheric CO₂. It is not a manufacturing defect – it is a storage history
Mercury	0.1 mg/kg max	Very low relative to the other metals – typically 30-50 times stricter than the arsenic limit. It points to a process or raw-material control specific to mercury
Arsenic	3 mg/kg max	Standard for food-grade alkali
Pb	5 mg/kg max	Individual limit, alongside the total
Heavy metals (as Pb)	10 mg/kg max	Aggregate limit; does not replace the individual ones
Clarity	Solution passes the test	Insoluble matter. A functional requirement in oil refining and in any clear-liquid application
Colour and odour	White or nearly white, odourless	Discolouration suggests iron contamination or organic pick-up
Texture	Flaky	Form factor, and a handling decision (see below)

5. Why the carbonate figure changes your dosing calculation

Potassium carbonate is not inert in an acid-base application – it neutralises acid too, and it does so at a different equivalent weight. That means a batch with 2% carbonate delivers slightly more total neutralising capacity than the KOH figure alone implies.

Calculation	Value
KOH as specified	85.0%
K₂CO₃ as specified	2.0%
KOH equivalent of the carbonate	2.0% x (2 x 56.11 / 138.21) = about 1.6%
Total alkali expressed as KOH	About 86.6%

The practical rule: if your process control is based on titration to a target pH, the carbonate does not matter much because you titrate to the endpoint anyway. If your process is based on weighing a calculated amount of KOH, then the carbonate figure has to be part of the calculation – and it will drift upward as the material sits in a partly used drum.

6. Form factor: flake, prill or liquid

Form	Typical concentration	Best fit
Flake	85-90%	Small to medium batch weighing; easy to handle in a food plant with dry ingredient dosing
Prill / granular	90%+	Lower dust, better flow in automated weighing; slower to dissolve than flake
Aqueous solution	45% or 50%	Large volume users, pumped dosing, no dissolution step – but you pay to ship water and need heated storage in winter

Flake is the default for food applications because it dissolves quickly and can be weighed accurately at small scale. Its disadvantage is hygroscopicity on the surface of the flakes, which is precisely where the carbonate forms.

7. Storage: the specification degrades in your warehouse

Potassium hydroxide is strongly hygroscopic and absorbs carbon dioxide from the air, converting to carbonate at the surface. Two consequences worth planning for:

Keep containers closed and the store dry. A drum opened repeatedly over months will show a rising carbonate figure and a falling KOH figure, both within specification but drifting in the same direction.
First in, first out – and buy to consumption. The material does not “go off” in a dramatic way; it slowly becomes a slightly different mixture, and if your process weighs rather than titrates, that difference reaches the product.

Also treat it as what it is: a corrosive alkali. Segregate from acids, protect from moisture, and follow the SDS for personal protective equipment and for spill response.

8. What to put on the purchase order

Grade and intended use – “food grade, for use as an acidity regulator” is a specification; “KOH 90%” is not.
Form and concentration – flake, prill or 45%/50% solution, because the price and handling differ completely.
Full impurity set: K₂CO₃, Hg, As, Pb, total heavy metals, clarity – not only the assay.
Food-safety certificate, with the certification body and the site named, plus its validity date.
Documentation package: COA per lot, SDS in the required language, specification sheet, and any allergen or GMO statement your market requires.

9. Packaging and supply

Food-grade potassium hydroxide ships in flake or prill form in polyethylene-lined steel drums, in 25 kg bags with a moisture barrier, or in big bags; solutions ship in HDPE drums, IBCs or road tankers. Because moisture and carbon dioxide are the two degradation routes, packaging is chosen for barrier performance rather than for freight economics, and pack size is agreed against your consumption so that a drum is used within its useful life. Every lot ships with a COA and SDS, FOB or CIF against destination, and the food-safety certificate is supplied with the first order and updated at each renewal.