Dear Steve and Listserve
I would like to add to Jon McGraw's observations.
The mere act of freezing, and necessary subsequent thawing, produces changes
in the sensory properties of fish. They are of the same character as
produced by frozen storage - decrease in intensity of characteristic fresh
flavour, (assuming the fish is very fresh when frozen), development of cold
storage flavours or rancid flavours, development of tough, dry fibrous
texture, formation of 'drip'. A well trained/experienced sensory panel can
differentiate between unfrozen fillets and fillets frozen and immediately
thawed. The effect though is small if freezing and thawing is carried out
under good practices and has little implication for consumer satisfaction -
the effects of holding frozen fish at inappropriate storage temperature
would be much greater . The changes described, especially in loss of fresh
flavour, are most rapid in the temperature range of about -2ºC to -5ºC and
this range should be passed through as quickly as possible. Double freezing,
and thawing, will incur two double excursions through this zone and the
effects on sensory properties will be accumulative, but still within limits
of acceptability for good quality products, again assuming good practices.
These practices include starting with very fresh fish, preferable sea
frozen, rapid freezing and rapid thawing. Much of the consumer products such
as coated fish portions are prepared from double frozen material. The fish
are frozen at sea, returned to land processing plants for thawing and
filleting, and refrozen as blocks. This is approximately the scenario
described by Steve.
Steve asks for literature. I do not have any papers in my own bibliography,
but Dr Schubring of the German fisheries laboratory in Hamburg has published
papers on double freezing. The FAO publication Johnston, W.A., Nicholson,
F.J., Roger, A. & Stroud, G.D. 1994, Freezing and refrigerated storage in
fisheries. FAO Fisheries Technical Paper 340, FAO, Rome, Italy, has a brief
reference, p7:
"This practice [double freezing] is often necessary for the production of
some frozen fish products previously made from fish frozen and stored in
bulk. What must be remembered is that even quick freeing results in quality
changes in fish and double freezing will therefore result in further
changes. Only fish that were initially very fresh should therefore be
subjected to double freezing and still conform to good quality standards.
Fish frozen quickly at sea immediately after catching, for instance, would
be suitable for this purpose."
Peter Howgate
----- Original Message -----
From: "Steve Grabacki" <graystar@alaska.net>
To: "Seafood Internet" <seafood@ucdavis.edu>
Sent: Thursday, March 11, 2004 3:03 AM
Subject: twice-frozen salmon
> Greetings -- How does twice-frozen salmon differ from once-frozen
product?
> Example -- Salmon #1 is filleted, and the fillets are frozen. Salmon #2
is
> headed-and-gutted, then frozen, later thawed, then filleted, then the
> fillets are frozen. How apparent is the difference between the fillets of
> fish #1 vs. fish #2? What are the specific differences (texture, etc.)?
> Are there any papers or reports of studies on this topic? Thanks &
Cheers,
> -- Steve
>
> Stephen T. (Steve) Grabacki, FP-C
> President
> GRAYSTAR Pacific Seafood, Ltd.
> P.O.Box 100506
> Anchorage, Alaska
> 99510-0506 USA
> ph: +907-272-5600
> fx: +907-272-5603
> graystar@alaska.net
>
>
>
>
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