Peter,
Good point. A blast boat is a relatively small boat 15 to 20 meters that
freezes the fish in the fish hold with a blast (cold circulating air) freezer. The
fish remain in the hold for the duration of the trip as they were originally
placed. Defrost cycles are programmed usually once every 24 hours. These
cycles which are simillar to the defrost cycles in your frost free home
refrigerator freezer simply defrost the system by moving warmer air through the system to
melt any accumulated frost. In times of heavy fishing the temp of the hold
can vary substantially causing core temperatures of frozen tuna to "warm" from
-20F to -2F. These temperature fluctuations were measured by the use of
internal time/temp probes placed into the core of the fish prior to initial freezing.
At unloading the core temps of the fish will lose as much as 15F (from -20F
to -5F) if left in ambient air temps (60F) at dockside. I am sure that most
tuna people out there have observed tuna in bins at dockside waiting to be moved
into the transport vessel or a cold store freezer (-20F to 0F)or at least a
chill store at 32F. In one instance I observed and recorded tuna that was taken
from a -20F fish hold at 9AM and remain in a metal bin at ambient air
conditions until 4PM when the lory showed up for transport which only held the fish at
0F. I suppose that if the fish are on their way to processing then this could
be view as defrosting. But what happens if that -20F is left to thaw to 15F
then refrozen to 0F. I would think there would be some recrystallization form
thus damaging cellular structure. Could anyone shed any light on this?
I would think that the temperrature swings in shrimp would be greater under
the same conditions because of the density of the product.
Paul Dion
Paul Dion Associates, Inc.
Plymouth, MA
USA
In a message dated 11/26/2004 5:07:20 AM Eastern Standard Time,
phowgate@clara.co.uk writes:
> Subj: Re: frozen product core temp
> Date: 11/26/2004 5:07:20 AM Eastern Standard Time
> From: phowgate@clara.co.uk
> To: PDIONPDA@aol.com
> CC: seafood@ucdavis.edu
>
Sent from the Internet
Can Paul Dion expand on his message. What is a ‘blast boat’ and what is
involved in a ‘defrost cycle’. Were the tuna in the ship’s cold store? How was
the temperature of the product measured? The temperature range he quotes is
quite extraordinary for the temperature fluctuation of product that would be
expected in the defrost cycle of a cold store.
While I’m writing, let me go back to the original message. Enrique is quite
correct of course; codes of practice, international transport agreements,
regulations and such like recommend or specify the maximum temperature for storage
of frozen foods. I am not aware of any regulations or similar relating to
minimum temperatures of storage, though I am aware of quality assurance
specifications of some fish processing companies that requires storage at lower
temperatures, usually below -25 degC. Manuals of handling of frozen fish such as FAO
Fisheries Technical Paper 340, Freezing and Refrigerated Storage in Fisheries,
usually recommend that frozen fishery products be stored at -30 degC. The good
quality storage life of fishery products, including shrimp, is around 3
months at -18 degC, which bearing in mind inevitable delays in the distribution
chain is not long enough to ensure a good quality product to the consumer.
Peter Howgate
> ----- Original Message -----
> From: PDIONPDA@aol.com
> To: jn@dfu.min.dk
> Cc: seafood@ucdavis.edu
> Sent: Friday, November 26, 2004 2:49 AM
> Subject: Re: frozen product core temp
>
>
> Jette,
>
> How does the fluctuation of temperatures between -20C &-30C effect quality?
> I have seen frozen tuna fluctuate onboard from -20F to 0F during defrost
> cycles on blast boats. Dockside buyers and processors do not seem to care or
> maybe it is just that they are unaware of these temperatrure swings during
> onboard holding, unloading and transport.
>
> Paul Dion
> Paul Dion Associates, Inc.
> Plymouth, MA
> USA
>
In a message dated 11/26/2004 5:07:20 AM Eastern Standard Time,
phowgate@clara.co.uk writes:
> Subj: Re: frozen product core temp
> Date: 11/26/2004 5:07:20 AM Eastern Standard Time
> From: phowgate@clara.co.uk
> To: PDIONPDA@aol.com
> CC: seafood@ucdavis.edu
> Sent from the Internet
>
>
>
> Can Paul Dion expand on his message. What is a ‘blast boat’ and what is
> involved in a ‘defrost cycle’. Were the tuna in the ship’s cold store? How was
> the temperature of the product measured? The temperature range he quotes is
> quite extraordinary for the temperature fluctuation of product that would be
> expected in the defrost cycle of a cold store.
>
> While I’m writing, let me go back to the original message. Enrique is quite
> correct of course; codes of practice, international transport agreements,
> regulations and such like recommend or specify the maximum temperature for
> storage of frozen foods. I am not aware of any regulations or similar relating to
> minimum temperatures of storage, though I am aware of quality assurance
> specifications of some fish processing companies that requires storage at lower
> temperatures, usually below -25 degC. Manuals of handling of frozen fish such
> as FAO Fisheries Technical Paper 340, Freezing and Refrigerated Storage in
> Fisheries, usually recommend that frozen fishery products be stored at -30
> degC. The good quality storage life of fishery products, including shrimp, is
> around 3 months at -18 degC, which bearing in mind inevitable delays in the
> distribution chain is not long enough to ensure a good quality product to the
> consumer.
>
> Peter Howgate
>
>
>
> >> ----- Original Message -----
>> From: PDIONPDA@aol.com
>> To: jn@dfu.min.dk
>> Cc: seafood@ucdavis.edu
>> Sent: Friday, November 26, 2004 2:49 AM
>> Subject: Re: frozen product core temp
>>
>>
>> Jette,
>>
>> How does the fluctuation of temperatures between -20C &-30C effect quality?
>> I have seen frozen tuna fluctuate onboard from -20F to 0F during defrost
>> cycles on blast boats. Dockside buyers and processors do not seem to care or
>> maybe it is just that they are unaware of these temperatrure swings during
>> onboard holding, unloading and transport.
>>
>> Paul Dion
>> Paul Dion Associates, Inc.
>> Plymouth, MA
>> USA
>>
>
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