Dehydrated onion is not steam sterilised by default, but it can be, and many food manufacturers in the EU, UK and US ask for it. The treatment reduces total plate count, yeast and mould, and pathogens such as Salmonella.
Done well, the effect on flavour is usually small. The bigger risks are a slight darkening of colour, some loss of the sharpest volatile notes, and lumping in fine powders if moisture is not brought back down after treatment.
How it is done
The product is exposed to saturated steam for a controlled time and temperature, then dried and cooled back to its moisture spec. Some plants treat flakes and then mill them into powder in hygienic conditions. Others treat the finished form directly. The general principles are covered in what steam sterilisation is and when you need it.
Not every Mahuva plant has its own sterilisation unit. Some send product to a separate treatment facility. That is acceptable if the facility is audited and the goods are tracked by lot in both directions.
Effects to test for
- Colour: treated onion can be slightly darker or more yellow than untreated product of the same grade.
- Aroma: some of the fresh, sharp top notes may soften.
- Flow: powders and granules may lump if moisture rises during treatment.
- Moisture: must be brought back within spec before packing.
- Microbiology: counts should fall clearly, which you confirm with a lab test after treatment.
Untreated, low count and sterilised
Suppliers may offer untreated product, product described as low microbial, and steam sterilised product. Low microbial can mean better hygiene and selection, or a light treatment. Ask exactly what process was used and get the microbiology results that back the claim.
If your onion will be cooked thoroughly in your process, untreated goods may be acceptable. If it goes into uncooked foods, a validated kill step is usually expected. Your own food safety plan and your customers decide.
What not to accept
Do not accept ethylene oxide fumigation as a way to cut microbes. Its use on food is not permitted in the EU, and residues have caused large recalls of Indian sesame and spices. Write "no ETO treatment" into the spec and test for ethylene oxide and 2-chloroethanol. Our guide to ETO treatment and EU rejections explains why.
Irradiation is another method, but it is restricted and must be labelled in the EU. If you do not want it, say so in the contract.
Before you order
- Approve a sample that has been through the same treatment as your shipment.
- Ask for the process records for the lot: time, temperature and batch size.
- Test microbiology after treatment, not before.
- Check colour and moisture against your spec after treatment.
- Confirm where treatment happens and who owns the unit.
How we help
We confirm whether a plant sterilises in house or outside, visit the treatment unit, and check that lot records match. Post-treatment samples go to an NABL-accredited lab for microbiology, moisture and ETO. Ask for a free sourcing review.