Sodium Hexametaphosphate (SHMP) — Frequently Asked Questions

Frozen fish and shellfish lose water as drip when they are thawed and cooked, which reduces yield and makes the flesh dry and fibrous. Polyphosphate treatment, often a blend containing SHMP, helps the proteins retain their natural moisture and protects texture through freezing. In canned seafood SHMP also binds magnesium, which helps prevent glassy struvite crystals forming. Use must stay within the P2O5 limit for the category, and excessive treatment to add water is not permitted.

Each does a different job, which is why blends are common. TSPP is alkaline and the most effective at dissociating muscle proteins, improving water holding and bind. STPP is the workhorse of meat brines, balancing pH lift and solubility. SHMP is near-neutral and a strong sequestrant, so it improves solubility of the blend in hard water and stabilises colour and flavour. The ratio is chosen for the product and the brine, then confirmed in yield and sensory trials.

The name is historical. Early chemists believed the glassy product was a ring of six phosphate units. It is now known to be a mixture of long-chain polyphosphates with an average chain length that varies between grades. That is why specifications focus on total and inactive P2O5 and on solution pH rather than on a single molecular formula.

Yes, slowly. Long polyphosphate chains hydrolyse in water to shorter pyrophosphate and orthophosphate, losing sequestering power. The process speeds up with heat and at low pH. Make brines and stock solutions fresh, keep them cool, and use them within the same shift where possible. Dissolve the phosphate before adding salt, because high salt concentrations slow dissolution.

Most food categories that allow phosphates set one group maximum for E338 to E452 combined, expressed as P2O5, so add the contribution of every phosphate in the recipe, including those from other ingredients. The limit and the categories are in Annex II of Regulation (EC) No 1333/2008 and the UK retained equivalent. On the label SHMP is declared by function and name or E-number, for example stabiliser: E452.

Tell us the application, the form required (glassy flake, granule or powder), the minimum P2O5 and any limit on inactive phosphate, the purity standard (E452(i), FCC or JECFA), pack size, annual volume and destination. List the approval documents you need, such as the specification, safety data sheet and batch certificate of analysis, so they can be confirmed with the quotation.