Chinling
We must be clear about terminology here. In my messages I meant 'slurry ice'
or perhaps better, 'ice slurry', to be a mixture of ice and freshwater or
sea water prepared by adding particulate ice, for example, crushed block ice
or flake ice, to water in a container. The container can be a large tank in
a ship when the system is usually referred to as CSW, chilled sea water. The
fishery product is immersed in this. This way of cooling fish has been used
for a long time in the fishing industry to cool fish. The slurry should be
thick before the fish/shrimp are added; a mixture of 1:4 water:ice would be
typical. This mixture is made from the separate ingredients and the ice is
dry, that is the methods of preparation and storage allow any free water to
drain away from it.
Flake ice is made in a scraped heat exchanger and if the conditions are
arranged so that some of the water is not frozen what is produced is a
mixture of flake ice and water. This mixture is referred as 'slush ice' -
see FAO Fisheries Technical Paper 331, Ice in Fisheries, FAO,1992. This
publication notes that a mixture of flake ice in 10% water is pumpable. This
system was develop further so that the scraped heat exchanger system
produced very small particles of ice suspended in a liquid. Originally I
understand these mixtures were intended as heat exchange fluids that could
be circulated through pipework, and continue to be used as such, and a
variety of liquids are used. The slurries can also be used to directly cool
foodstuffs, including fishery products, and then the fluid must be potable.
For fishery products sea water is frequently used. These slurries are
referred to in the FAO publication as 'slush ice', but in the refrigeration
industry more often as 'pumpable ices'. They are sometimes referred as
'binary ices' or 'biphasic ices' because they can be considered as two
phases - solid ice and the fluid the ice is suspended in. Accounts I have
read of the use of pumpable ices in fishery industry the slurries have
contained 60% of the liquid phase. Such slurries are used on fishing vessels
in the UK and in other countries, but I do not know how extensively. Being
almost liquid pumpable ice makes a good heat exchange medium and fish cools
more rapidly in pumpable ices than in flake ice, but I think the main
advantage of its use on fishing vessels is its ease and convenience of use
rather than its cooling efficiency.
A feature of pumpable ice as I have described is that its temperature is
below 0degC. If the ice is made from sea water, approximately 3% salt
solution, and ends up as a slurry containing 60% liquid phase then the
liquid phase is effectively 5% brine and the temperature of the slurry is at
about -3degC. Most of the cooling capacity of ice is in the latent heat of
the melting of the ice rather than the temperature of the medium and a
greater weight of pumpable ice containing 40% ice will be required to cool a
given mass of fish than of flake ice, about twice as much. However, there is
no doubt that fishery products cool faster in pumpable ice, or any other
type of ice slurry for that matter, than with flake ice. However, as
Professor Labuza pointed out a small product such as shrimp will cool
rapidly anyway so the advantage of the close contact obtained with slurries
compared with flake ice may not be of much advantage in the case of cooling
of shrimp. Pumpable ices are used to cool fishery products stowed in boxes,
not in closed containers, and the liquid phase with drain away leaving
almost pure ice so the system ends up similar to that of stowing the product
in flake ice.
The original question asked about storing fish in slush ice as distinct from
cooling in slush ice, and I advised against it on the assumption the slush
ice system was as I described above, in a non-draining container. My main
objection was to the undesirability of allowing shrimp to remain immersed in
water. This situation does not arise if pumpable ice is used to ice up
shrimps for storage in boxes and whether to use it or flake ice seems to me
to be a question of economics - costs of purchase and maintaining a pumpable
ice system compared with a flake ice machine - and of convenience.
To deal with the second part of your message, that of flavour of shrimps.
The experiments on leaching of flavourous substances were carried out as
part of a study of processing of cooked/peeled shrimps I was involved in
many years ago. It was obvious that the multiple washings that cooked peeled
shrimp were subjected to, in addition to soaking in ice/water slurries,
would leach out flavours and I measured ninhydrin-reacting substances -
predominately amino acids - as a quantitative measure of this leaching. The
experiment was not large enough to warrant publication and I no longer have
my notes of the exercise. The results just confirmed what was obvious from
tasting the products - that flavour was rapidly lost as the shrimp went
through the processing and the final product was tasteless.
I am not aware of any comprehensive account of the flavour and flavour
chemistry of shrimps and of the differences between species. My own
experience is that there are species differences and the differences are
mainly in the sweetness of the products. This sweetness is due to amino
acids such as glycine and alanine present in high concentrations in
crustacean shellfish, possible potentiated by inosine monophosphate. I have
not seen comparative amino acid analyses of shrimp, but the sweetest shrimp
I have tasted has been deepwater rose shrimp caught off Mauritania.. Close
to that is scampi, Nephrops norvegicus, caught off northern Scotland. In the
laboratory I worked in some members of my taste panels would not attend
scampi tastings because they disliked the strong sweet flavour. I have found
the shrimp I have tasted in SE Asia to be less sweet than these species, but
I can not recall my experiences of different species. I have noted an
earthy/musty flavours of some shrimp from SE Asia and I assume these must
have been farmed in freshwater ponds. I have come across the term sticky
shrimp in association, but this due to the glaze applied to the shrimp as
part of a cooking recipe. I am not aware of washing making a difference to
the stickiness of the raw shrimp, but I have a recollection of the effect of
icing on the sound that shell-on shrimp make when being poured out of a box.
However I can appreciate Japanese customers asking for minimally washed
shrimp as these will have retained their flavour.
Peter Howgate
----- Original Message -----
From: "Chingling Tanco" <crt@mida-group.com>
To: "P Howgate" <phowgate@clara.co.uk>; <seafood@ucdavis.edu>
Sent: Wednesday, June 27, 2007 2:12 AM
Subject: Re: Chilled Storage of Fresh Fish (tuna)
Thanks for this Peter,
The ice slurry equipment people say the ice slurry advantage is the ability
to transport the ice through a processing plant through pipes rather than
have all kinds of carts just to transport ice. Also, with flake ice rooms,
you then deal with the problems of how to keep that room sanitized and have
workers change boots when they enter to get ice, and then how to properly
transport the ice through a plant.
We are in the process of trying to rebuild the shrimp industry in the
Philippines and know that plants will be having to upgrade from the old
system of having ice blocks and crushing them. Only a few have flake ice
machines which by the way normally I understand (from the same slurry ice
equipment people), operate to only about 80% of rated capacity.
So as the industry here rebuilds their plants and look at investing in flake
ice or slurr ice equipment, your discussion plus that of Remi re EU FVO
requirements, will make a difference.
I am also interested in your studies on the leaching out of amino acids
and which are the flavoring compounds or flavor potentiators. You are
saying that your study showed that there was more loss in these flavor
compounds when ice slurry was used rather than with flake ice? Is this
study or paper already published and would it be possible to see a copy of
it?
We have gotten comments on the blandness of the flavor of the vannamei vs
the tiger from our distribution markets here. Are these flavoring compounds
measureable? In Indonesia there is a product some people are producing for
the Japanese market called Sticky shrimp they mean for the shrimp to be
washed as little as possible thus retaining the sticky surface. Wonder if
this has to do with the retention of those flavoring compounds you talk
about.
Chingling Tanco
Mida, Philippines
On 6/21/07 11:40 PM, "P Howgate" <phowgate@clara.co.uk> wrote:
> Chingling
>
> As Professor Labuza points out shrimp will cool within a few minutes in
> ice
> slurry. The time will be a little longer when stowed in flake ice, but the
> difference will not be of any technological significance. The question
> then
> is the balance of advantages/disadvantages between the two processes.
> There
> is no doubt in my mind that stowing in flake ice is to be preferred. I
> described in my previous message the disadvantages of bulk and weight and
> of
> the need to use more ice when using ice slurry and the possibility of
> layering of water and ice, but I must emphasis in the case of shrimp the
> penalty of leaching out flavourous compounds in the case of small products
> such as shrimp. I have carried out experiments on the leaching of amino
> acids, some of which are flavouring compounds themselves or flavour
> potentiators, but can be considered as representative of other flavouring
> chemicals such as nucleotides, and monitored the losses during processing.
> The loss of flavour is more pronounced in the case of headless and is
> severe
> in the case of peeled. In some cooked/peeled plants I looked at by the
> time
> the cooked shrimps were held in ice slurry, cooled in ice slurry after
> cooking, washed, and left standing in ice slurry between processing steps
> there was hardly any amino acids and other flavouring chemical remaining
> and
> the products were tasteless.
>
> I would recommend that shrimp be iced in flake ice rather than crushed ice
> as the large lumps in the latter can bruise the shells, which promotes
> formation of black spot, and they should be iced in shallow boxes to avoid
> compression damage, which again promotes formation of black spot. Cooling
> and stowage in ice slurry prevents this damage, but I consider that this
> benefit does not compensate for the disadvantages of this technique.
>
> Peter Howgate
>
> ----- Original Message -----
> From: "Chingling Tanco" <crt@mida-group.com>
> To: "P Howgate" <phowgate@clara.co.uk>; "Dinesh Dhammika uduwana"
> <dduduwana@hotmail.com>; <seafood@ucdavis.edu>
> Sent: Tuesday, June 19, 2007 9:00 PM
> Subject: Re: Chilled Storage of Fresh Fish (tuna)
>
>
>> Hi Peter,
>>
>> What about if you were cooling shrimp - say 15-20 grams per piece HO or
>> 10-20 grams headless. Because of the size of the shrimp, heat diffusion
>> within the animal will not be much of an issue so does this make ice
>> slurry
>> more effective for cooling shrimp? What about storing shrimp overnight?
>>
>> Chingling Tanco
>> Mida Trade Manila
>>
>>
>> On 6/19/07 10:30 PM, "P Howgate" <phowgate@clara.co.uk> wrote:
>>
>>> Dinesh
>>>
>>> You need to differentiate between cooling fish in ice slurry and storing
>>> fish in ice slurry.
>>>
>>> Ice slurry, because it is in complete contact with the surface of the
>>> fish,
>>> is a better heat transfer medium than is flake ice and could be the
>>> preferred procedure for cooling large, warm fish such as tuna. However
>>> flake
>>> ice also makes good contact with the surface of the fish plus the melt
>>> water
>>> from the ice trickles over the fish making good contact with the fish.
>>> Also
>>> there comes a point in the cooling when surface heat transfer is not the
>>> limiting factor for heat loss compared with heat diffusion within the
>>> fish.
>>> Altogether there is not likely to be a big difference in rates of
>>> cooling
>>> between the 2 systems, but you would have to carry out comparative
>>> experiments to determine the size of the difference in your
>>> circumstances.
>>> Ice slurries use more ice to cool a given mass of fish than using flake
>>> ice
>>> because the water in the slurry has to be cooled down as well as the
>>> fish
>>> so
>>> is more costly than using flake. It is important when cooling fish in
>>> ice
>>> slurries that the mixture is stirred or the water phase recirculated.
>>> When
>>> the fish is added to the slurry some of the ice is melted and the
>>> container
>>> has layer of water and fish with the ice floating on top of it. If the
>>> fish
>>> has not cooled down completely this layer of fish and water will
>>> equilibrate
>>> at a temperature above 0degC and the ice floating on top will not cool
>>> it
>>> down. This does not happen with fish stowed in ice; assuming there is an
>>> adequate amount of ice all of the fish will cool down to ice
>>> temperature,
>>> (actually a little below it, around -0.2degC, to be pedantic). Chilled
>>> Seawater (CSW) systems - a slurry of ice with seawater- are often used
>>> on
>>> pelagic trawlers to cool large catches of pelagic fish, but these
>>> systems
>>> recirculate the water to ensure mixing. CSW is not the same as the
>>> refrigerated brine storage used on larger tuna boats.
>>>
>>> Though ice slurry is effective in rapidly cooling fish when used
>>> properly
>>> it
>>> is not a good medium or procedure for storing fish. Fish in ice slurry
>>> takes
>>> up more space, and weighs more than the same amount of fish in ice.
>>> These
>>> are considerations for the space required to store the fish and for
>>> transporting it. Suspension in water alters the appearance of the fish.
>>> This
>>> might not be a consideration for tuna destined for canning but is for
>>> fish
>>> going to retail sale. Depending how long the fish is stored in the ice
>>> slurry the product can lose flavour due to leaching into the water, and
>>> the
>>> fish can absorb water. This might be favourable for the economics of
>>> selling
>>> the product, but not for eating quality.
>>>
>>> The Codex advice, and other texts on storage of fish, that fish should
>>> iced
>>> in containers which allow for drainage is good advice and should be
>>> followed. Fish in ice slurries are typically held in containers with a
>>> drainage hole; just taking the bung out of the hole will allow for
>>> drainage.
>>>
>>> Peter Howgate
>>>
>>> ----- Original Message -----
>>> From: "Dinesh Dhammika uduwana" <dduduwana@hotmail.com>
>>> To: <seafood@ucdavis.edu>
>>> Sent: Saturday, June 16, 2007 12:07 PM
>>> Subject: Chilled Storage of Fresh Fish (tuna)
>>>
>>>
>>>> Dear All in Seafood List,
>>>>
>>>> Looking forward for the expert opinion on what is the best way of
>>>> storage
>>>> of fresh fish either only ice (flake Ice) or in a ice slurry
>>>> composites
>>>> of flake ice and water.
>>>>
>>>> code of hygienic practices for the fresh fish (Codex) says the water
>>>> from
>>>> melting ice should be drained to prevents bacteriological and chemical
>>>> contamination!
>>>>
>>>> so if we stored in a ice slurry how can we facilitate drainage in
>>>> stored
>>>> in ice slurry!
>>>>
>>>> expecting expert comments soon.
>>>>
>>>> thanking you
>>>>
>>>> Dinesh Dhammika
>>>> Ensis Fisheries Factory
>>>>
>>>> _________________________________________________________________
>>>> Don't just search. Find. Check out the new MSN Search!
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>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
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