Hello everyone, here are some comments from a trader in the industry:
1. what are the temperature terms you are all using -
-18ºC and -20̊C
2. On the -50 vs -65degrees C freezing of fish, i know this terminology
refers to being able to maintain fish as sashimi grade. A distinction is
made commercially on frozen on board fish in commercial vessels and product
frozen at -50 degrees or less can be considered sashimi grade and product
frozen at -40 degrees or more is considered A-Grade. This is used for
Tuna, and for Swordfish. You can see the distincition in the bloodline of
the fish.
Further more, fish that may have originally been sashimi grade but not
stored in -50 degrees will lose its sashimi quality.
3. As to quality deterioration during storage - i once had an ineresting
conversation with a technical person from Stahl Astra - the makers of the
screw type compressor. He said that there is something called the delta T
factor which refers to the difference between the temperature of the cold
storage and the temperature outside the cold storage. if the Delta T is
high, there will be more loss of weight during storage than if the Delta T
is lower. Does anyone know anything more about this?
4. Question for the peanut gallery. Is it always true that the faster the
freeze, the closer to retaining the quality of it's prefrozen state is a
product? So something frozen by nitrogen will be better than if it were
frozen in 4 hours?
Chingling Tanco
At 09:05 AM 1/11/2003 +0000, P Howgate wrote:
>Dear List
>
>I can not agree with Dr Peralta, in respect to effect on quality, that '...
>the freezing process is as important as the storage temperature'. In my
>experience of evaluating many samples of fish frozen in different ways the
>rate of freezing other than very slow freezing, over days, has a negligible
>effect on quality. Storage temperature has a large effect on quality. An
>experienced sensory panel can detect the effect of 2 weeks storage at -18ºC,
>for example. The FAO publication Jose refers to is probably the FAO
>Fisheries Technical Paper 340, Freezing and refrigerated storage in
>fisheries, cited in my message of the 9th. Let me quote from this
>publication from the section on freezing methods:
>
>'There is no widely accepted definition of quick freezing.
>
>It is unlikely that even a trained taste panel could detect the difference
>between fish frozen in 1h and 8h, but once freezing times begin to extend
>beyond 12h the difference may well become apparent. Freezing times of up to
>24h or even longer, achieved in some badly designed and operated freezers,
>will almost certainly result in an inferior product. Very long freezing
>times, for example, due to freezing fish by bulk stacking in a cold store,
>may even result in spoilage by bacterial action before the middle of the
>stack is sufficiently reduced in temperature.
>
>Since the temperature just below 0ºC is the critical zone for spoilage by
>protein denaturation, an early UK definition of quick freezing recommended
>that all the fish should be reduced from a temperature of 0ºC to -5ºC in 2h
>or less. The fish should then be further reduced in temperature so that its
>average temperature at the end of the freezing process is equivalent to the
>recommended storage temperature of -30̊C. With normal freezing practice in
>the UK, this latter requirement is defined by stating that the warmest part
>of the fish is reduced to -20̊C at the completion of freezing. When this
>temperature is reached, the coldest parts of the fish will be at, or near,
>the refrigerant temperature of say -35̊C and the average temperature will
>then be near -30̊C. This is a rather elaborate definition of quick freezing
>and it is probably more strict than is necessary to ensure a good quality
>product.
>
>The more widely used definitions of quick freezing do not specify a freezing
>time or even a freezing rate but merely state that the fish should be frozen
>quickly and reduced in the freezer to the intended storage temperature.'
>
>The requirement for good freezing practice is just that the product be
>frozen in equipment designed for the freezing of fishery products. This is
>quite adequate and precludes just putting products in a cold room to freeze.
>
>I also should mention that thawing is an important step in the process of
>utilising frozen fish. Again the thawing process should be fast, for example
>in mechanical thawers, for maintenance of good quality.
>
>Peter Howgate
>----------------------------------
> > ----- Original Message -----
> > From: "Jose P. Peralta" <jperalta@gaechuk.gsnu.ac.kr>
> > To: <seafood@ucdavis.edu>
> > Sent: Friday, January 10, 2003 2:49 AM
> > Subject: Frozen fish vs its Quality
> >
> >
> > Dear list:
> > This posting somehow deviates from the original subject string, thus,
> > re-titled
> > differently.
> > The original subject string was, " Ice content in frozen fish."
> >
> > >>What is more damaging to quality is
> > that the fish has apparently been stored at -20ººC before processing and
>will
> > be stored at -18ººC afterwards. These temperatures are too high for
> > maintenance of good quality in frozen fish; a better temperature for
>storage> would be around -30ººC.
> >
> > I would agree that storing at -30 C is better. Furthermore, the freezing
> > process is as important as the storage temp. The thermal arrest period
> > should
> > be kept to 2 hours max.
> >
> > I recall, in one of FAOs reference, it advices frozen fish storage
> > around -30 C,
> > also.
> >
> > The international frozen fish industry have been slow in adopting such
> > advisory. Nowadays, more efficient refrigeration systems are available.
> > Industry practice still use -18 C storage temp.(also practiced in the
> > Philippines).
> >
> > Frozen black tiger prawn, in blocks, shipped from the Phil to Japan at -18
> > C.
> >
> > There is however, an interesting note on frozen fish vs its quality. Raw
> > fish
> > tuna market in Japan, has been dictating low temp practices of yellowfin
> > tuna to
> > be either chilled or frozen at -65 C.
> >
> > I have info gap on the storage of the frozen tuna, thereafter, but I
>believe
> > it
> > is lower than -18 C. Also, please take note, that the tuna will be eaten
> > raw,
> > eventually.
> >
> > There is one thing I am certain, though, the consumers in Japan demand to
> > have
> > the highest fish quality, and they are willing to pay the price for this
> > premium.
> >
> >
> > Jose P. Peralta
> >
> >
> >
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