Re: Milk stays colder in glass bottles?

at Fri, 14 Oct 2005 21:00:05 GMT in <y6xirvzstka.fsf@xxxxxxxxxxxxxxxx>,
rich@xxxxxxxxxxx (Richard Kaszeta) wrote :

>"Default User" <defaultuserbr@xxxxxxxxx> writes:
>> Conversely, once out the glass bottles will warm the milk faster.
>
>It's not just conduction, it's heat capacity as well. Usually the
>glass containers are thicker, and glass has a much higher heat
>capacity than plastic. So this can go either way, but usually the
>glass bottle of milk stays cold slightly longer.
>

There are a lot of effects going on here.

The basic, most significant effect is that, if they've both sat in the
refrigerator (kept at a constant temperature) long enough, they'll both be
the same temperature. Over the long run 2 items placed in an environment at
the same temperature be equal.

However, the glass bottle has more heat capacity and the paper carton has
lower thermal conductivity. This introduces many more variables.

With its higher heat capacity, it will take the glass bottle longer to warm
up initially upon removal from the refrigerator, but once it is warm it
will both stay warm longer and transfer the heat from outside more quickly
to the milk inside. So, past a critical point, the milk inside the bottle
will heat up faster. But below that point, it will heat up more slowly.

Meanwhile the paper carton will have the reverse properties. However, the
paper of the carton is significantly thinner, and this also has its impact
on thermal conduction, so you'd have to run some tests, I suspect, to
determine exactly in what temperature regions the glass vs. the paper were
faster or slower.

when you put both back in the fridge, the glass bottle will take longer to
reach the internal temperature of the fridge, if both paper and glass are
at the same temperature going back in.

Now we also have to look at the impact on the sensory system. While we
sense temperature to a degree (excuse the pun) to a large extent we sense
rate of heat transfer. Thus a cast-iron pot coming out of a hot oven feels
a LOT hotter than a sheet of aluminium foil. And this has an effect on what
we perceive when we pick up the containers.

With both a higher heat capacity and conductivity, the cold bottle draws
heat away from our hands much faster than the paper carton. So in our hands
the paper feels warmer because it doesn't draw the heat out. If you were to
do an experiment and bring both containers (presumably full) to a boil, the
bottle would similarly feel much hotter, because now the heat would flow
from hot bottle to hand. This is probably the source of the belief that
glass keeps milk colder.

Sounds like a job for "MythBusters"...

--
Alex Rast
ad.rast.7@xxxxxxxxxxxxxxxxxxxx
(remove d., .7, not, and .NOSPAM to reply)
.

Relevant Pages

  • Re: Milk stays colder in glass bottles?
    ... it's heat capacity as well. ... >>> glass containers are thicker, and glass has a much higher heat ... "Even milk keeps better in glass bottles - it stays colder." ...
    (rec.food.cooking)
  • Re: Name That Parasite!
    ... We are just coming into our AWFUL heat. ... I had an ELABORATE setup with misters and fans and tons of water because it is so horrid for them. ... Do you put a pinch of baking soda in their water? ... When I was flatting and had no fridge (and that was back when the milk was delivered and it was in nice glass bottles, not plastic or cardboard) I made a milk cooler by putting a plastic wrapper around a milk bottle so I'd be able to take it out, then building a plaster cast using an old net curtain and plaster of paris - like plaster casts for broken limbs pre-fibreglass. ...
    (sci.agriculture.poultry)
  • Charlotte Russe Parfaits
    ... |3 tablespoons black cherry preserves with Chambord liqueur or red ... |Combine sugar, cornstarch, and egg in a bowl; ... |Heat milk over medium-high heat in a medium heavy saucepan to 180 ...
    (uk.local.cumbria)
  • REC Pork Loin Braised in Milk
    ... Pork Loin Braised in Milk ... Heat the butter and oil over medium-high heat in a casserole large enough ... Add the salt, pepper and milk. ... for about 1 1/2 to 2 hours, until the meat is easily pierced by a fork. ...
    (rec.food.cooking)
  • Re: REC Pork Loin Braised in Milk
    ... Pork Loin Braised in Milk ... Heat the butter and oil over medium-high heat in a casserole large enough ... for about 1 1/2 to 2 hours, until the meat is easily pierced by a fork. ... and cook briskly until it darkens. ...
    (rec.food.cooking)