Nofima Warns: Fish May Turn Yellow if Frozen Too Fresh
October 2, 2025 | 1 min to read
Freezing haddock pre-rigor—before rigor mortis sets in—caused consistent yellowing and quality loss after 20 weeks, a phenomenon Nofima researchers call rigor energy yellowing, previously undescribed in the literature. In contrast, haddock frozen post-rigor showed no discoloration, suggesting industry practices should consider timing of freezing to avoid unexpected quality defects.
Freezing fish at the wrong moment could lead to surprising quality problems. New research from Nofima shows that freezing fish when it is “too fresh” can cause visible discoloration and quality loss – a finding that even surprised the scientists themselves.
We are used to thinking “The fresher, the better” when it comes to food – and perhaps especially seafood. But look at the picture: haddock that was processed and frozen pre-rigor – that is, so fresh that rigor mortis had not yet set in – consistently turned yellow after just 20 weeks in frozen storage.
“Yellowing caused by ‘rigor energy’ has not been described in scientific literature. It is likely that the industry has not been fully aware of how significant this can be,” says Nofima researcher Svein Kristian Stormo.
By contrast, haddock frozen post-rigor showed no signs of discolouration.
To learn more, please visit Nofima.