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
> >
> >
>
>
>
>
>
This archive was generated by hypermail 2b29 : Tue Jul 18 2000 - 09:22:07 PDT