Nitrate accumulates in certain vegetables, principally leafy ones such as spinach,
lettuce and rocket, and the amount depends on the species, the cultivar, the growing
season, the light conditions and the fertilisation regime. Winter and glasshouse
production generally shows higher levels than summer field production, because light
drives the plant’s conversion of nitrate.
The European Union sets maximum levels for nitrate in specified vegetable categories
under its contaminants framework. Those maxima lived for years in Regulation (EC)
1881/2006 and have since been recast into a successor instrument, with the categories
and values amended periodically. Check the current text rather than a figure quoted in
an older specification template – stale nitrate limits are one of the more common
errors in circulated documents.
For a frozen product the practical consequences are two. First, the raw material
sourcing has to account for it: a supplier buying winter-grown leafy material without
monitoring is exposed. Second, the control is a monitoring programme with results over
time, not a single certificate, because levels vary between fields and between cuts of
the same field.
Processing has some effect – washing and blanching remove a portion, since nitrate is
water-soluble – but as with pesticide residues, reduction during processing is not a
control and should never be relied on to bring non-compliant raw material into
specification.