Listers on the subject,
I fully agree with Dr. Strak that thermodynamic calculation should lead to
practical utility. As I have emphasized, the calculations should give the
practicioner the base ice requirement only. The amount of excess should be
learned from standard practice.
The issue of un-used ice, after the fishing trip, again, I fully agree with Dr.
Strak that it should be dis-carded, for reasons as stated.
Jose Peralta
Andrew Strak wrote:
> Ken,
>
> I think that the thermodynamics calculations shoulds lead to simple and
> applicable 'rules of thumb'. In our practical life there are simply too
> many variables and in particular concerning heat leaks on the vessels.
> Moreover, the cost of ice is in most instances substantially below the cost
> of fish, threfere if taking any risks I would prefer to cover them with some
> excess of ice. There can always be some delays in the trip or slips in the
> discharging schedule. And with psychrophilic bacteria there is a substantial
> difference in growth rate and final count at 0C or +2-3C after few days.
> Besides, you are never sure about the size of your prospective catch and
> consequently very often insulated fishing boats carry some unused ice back
> home. Though, some calculated wastage is already built-in into the system.
> The issue is what to do with that excess ice that after several days may be
> of poor microbiological quality and caking and the vessel hold needs
> cleaning, besides. I would recommend discarding it. Therefore it is very
> difficult to be precise although sometives there is such a need as in the
> case of the superchilled fish described by you that got partially frozen in
> the brine. But it would not happen with regular ice unless it is very fresh
> from the plant.
>
> Andrew Strak
>
> ----- Original Message -----
> From: "Ken .Hilderbrand" <ken.hilderbrand@hmsc.orst.edu>
> To: <abstrak@accesswave.ca>; <jperalta@iloilo.net>; <seafood@ucdavis.edu>
> Sent: Monday, July 17, 2000 1:01 AM
> Subject: RE: Amount of Ice to Chill Fish
>
> > To the "ice needed to chill fish" discussion gang,
> >
> > This is an interesting discussion of "rules of thumb" and the
> > "thermodynamics" of how to figure out how much ice a fisherman needs to
> > "properly?" chill fish. But please remember, the bottom line often is
> > determined by the question of "who is paying for the ice?" If the fish
> plant
> > is providing the ice "free" the fisherman will want to take all they can
> > get. If fisherman are paying for the ice they will try to keep it at a
> > minimum. But if the ice is limited in supply, then there is a strong
> desire,
> > both by fishermen and fish plants, to be accurate in figuring out the real
> > quantity needed to meet some temperature specification.
> >
> > Ken Hilderbrand
> >
> > -----Original Message-----
> > From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu]On
> > Behalf Of Andrew Strak
> > Sent: Sunday, July 16, 2000 8:37 AM
> > To: jperalta@iloilo.net; seafood@ucdavis.edu
> > Subject: Re: Amount of Ice to Chill Fish
> >
> >
> > And usually the industry goes by the rule of thumb that works quite well.
> > For refrigerated fish holds in the Northern hemisphere and the average
> > length of trips 7-10 days it can be 1 part of ice per 2 parts of fish with
> > more ice being added in summer or when the trip is longer. Certainly, the
> > ice distribution around the fish is also very important and that may
> depend
> > on the type of ice being used. It does not only cool the fish but also
> > keeps it apart while allowing for oxygen to penetrate. A direct fish to
> fish
> > contact sometimes leads to undesirable marks and skin discoloration;
> besides
> > some anaerobic spoilage may lead to bilgy odours. Moreover, melting of ice
> > is perceived as beneficial to the product since it moistens the skin.
> >
> > Andrew Strak
> >
> >
> >
> > ----- Original Message -----
> > From: "Ted Labuza" <tplabuza@tc.umn.edu>
> > To: <jperalta@iloilo.net>; <seafood@ucdavis.edu>
> > Sent: Sunday, July 16, 2000 12:11 PM
> > Subject: Re: Amount of Ice to Chill Fish
> >
> >
> > > Dr Perlata has a good idea (below) I will take it one more step
> > >
> > > We can create a ice to fish ratio
> > >
> > > mi/mf = (t1 - 0)/Lf = Tf/80
> > >
> > > This says the Kg ice needed per Kg fish (or Lb per lb for that mater) is
> > simply
> > > 80 divided by the fish temperature Thus
> > >
> > > for cold water where Tf = 5 the ratio is 5/80 = 0.06
> > >
> > > for moderate water temp Tf = 20 the ratio is ~ 0.25
> > >
> > > for warm water eg in the Phillipines Tf = 35 ratio is ~ 0.44
> > >
> > > using a cp of one also gives a 20% overcompensation which is in the
> right
> > > direction.
> > >
> > > The problem of couse is with a low ratio one may not get the ice
> throughly
> > mixed
> > > with the fish
> > >
> > > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >
> > > Responding to the message of <3971922A.9218B6BA@iloilo.net>
> > > from jperalta@iloilo.net:
> > > >
> > > > Dear all:
> > > >
> > > > Here is an alternative.
> > > >
> > > > And may I use SI units?
> > > >
> > > > Assuming no heat losses, and ice temp is 0 C (normal ice temp); and
> that
> > > > the final temp of fish sought is not lower than 0 C.
> > > >
> > > > Heat given off by the fish = Heat absorbed by melting ice
> > > >
> > > > mf cp (t1 - 0) = mi Lf
> > > >
> > > > where
> > > > mf is the mass of fish in kg;
> > > >
> > > > cp is the specific heat of fish; I agree with parameters stated
> earlier
> > > > but we could simplify further and make it 1(unity); kcal/kg-C
> > > >
> > > > t1 is the initial temp of the fish; C
> > > >
> > > > Lf is the latent heat of fusion of water; 80 kcal/kg; lastly
> > > >
> > > > m1 is the amount of ice; kg, (which is the one sought for), and could
> > > > easily be calculated.
> > > >
> > > > This calculation is a fast estimate of the base ice requirements.. We
> > > > normally use more than this value to compensate for transport heat
> > > > losses and other losses/factors.
> > > >
> > > > ----------
> > > >
> > > > Another alternative is to use a "rule of thumb"; the ratio of 1 part
> > > > ice to 2 parts fish. This seems to also satisfy the aforementioned
> > > > calculations, and also compensating for the other heat lossess.
> > > >
> > > > Then of course, this assumes that the initial fish temp to be at
> normal
> > > > water temp.; which is around 25 C.
> > > >
> > > > I hope this helps.
> > > >
> > > >
> > > > Best regards,
> > > >
> > > > Jose
> > > >
> > > >
> > > >
> > > > --
> > > > -----------------------
> > > > Jose P. Peralta, Ph. D.
> > > > Professor/Food Engineer
> > > > Inst. of Fish Processing Technology
> > > > College of Fisheries, Univ of the Phil Visayas
> > > > 5023 Miag-ao, Iloilo, Philippines
> > > > Tel (63 33) 315 8289
> > > > FX (63 33) 315 8289, 315 8353
> > > > Cell (0917) 302 1282
> > > > EMail jperalta@loilo.net
> > > > ------------------------
> > > >
> > > >
> > > > .
> > >
> > >
> > > Dr Ted Labuza tplabuza@tc.umn.edu
> > > Prof. of Food Science Dept. of Food Science & Nutrition 136 ABLMS U of
> > Minn St
> > > Paul, MN 55108 Voice 612-624-9701 Fax 612-625-5272 home fax
> 651-483-3302
> > > cellemail 6126697885@mobile.att.net
> > > http://fscn.che.umn.edu/Ted_Labuza/tpl.html
> > > "SURFING THE WAVES OF CYBERSPACE"
> > > ___
> > > |กก|
> > > | \|
> > > |__| "The attitude of an engineer must be different than
> > > | that of a mathematician. The engineer is concerned
> with
> > > ---|---- truth, not mere consistency." Biot
> > > / \
> > > |___/__/\_____/
> > > \ /\ /\ /\/\/\
> > > \ /\ / \/ \ /\/
> > > "Before I came here I was confused about this subject. Having listened
> > to your
> > > lecture I am still confused But on a higher level."- E. Fermi
> > >
> > >
> >
> >
> >
> >
> >
-- ----------------------- Jose P. Peralta, Ph. D. Professor/Food Engineer Inst. of Fish Processing Technology College of Fisheries, Univ of the Phil Visayas 5023 Miag-ao, Iloilo, Philippines Tel (63 33) 315 8289 FX (63 33) 315 8289, 315 8353 Cell (0917) 302 1282 EMail jperalta@loilo.net ------------------------
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