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Lambic Digest #1022
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Subject: Lambic Digest #1022 (February 03, 1997)
Lambic Digest #1022 Mon 03 February 1997
Forum on Lambic Beers (and other Belgian beer styles)
Mike Sharp, Digest Coordinator
Contents:
pouring plates (Steve Daughhetee)
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Date: Sun, 2 Feb 1997 19:06:13 -0800
From: Steve Daughhetee <sdd6 at cornell.edu>
Subject: pouring plates
In LD #1020, Harlan Bauer described his petri-plate pouring technique:
>4. Pour into glass petri dishes
>
>5. Pressure cook for 15-min. at 15-lbs. psi, after allowing steam to escape
>for 10-min.
>
>5. Place cooker in clean-room after pressure has dropped to zero, keeping
>petcock closed, and allow to cool completely overnight, and open in morning.
Does the volume of media in the plates appear to change significantly with
pressure cooking? My hunch is that condensation is taking place during the
cooling phase and that this is diluting the agar in your plates. Even if
the volume doesn't change significantly, condensation which drips onto the
surface of the cooling agar could dilute this surface layer and make it
soft. You might check if your plates are firmer on the bottom than the
top.
If you could open the cooker after pressure had dropped to zero and remove
the plates to cool on the counter (without spilling), your technique might
work better.
I'll suggest an approach which is closer to how we do it in a lab but which
is suitable for home equipment. Since the plates are poured cooler and are
allowed to cool in a lower humidity environment, there is much less
condensation on the lids and consequently much less dilution of the surface
agar.
As this procedure involves handling very hot and somewhat sticky liquids,
caution must be exercised.
1. Clean glass petri dishes, stack (assembled, right side up), and wrap in
aluminum foil. Pressure cook on a rack, so they don't get too wet.
Following sterilization, bake dry in a warm oven. Let cool to room
temperature.
2. Combine agar and clarified wort in a suitable container, such as a
canning jar or an Erlenmeyer flask (it's a lot easier to pour from a
flask). Don't fill more than half full, to prevent boilover. Cover top of
container with a double layer of aluminum foil (like a hat). Pressure cook
as before. Allow to cool slowly until pressure has dropped to zero. Wait
additional15 minutes before opening cooker (to minimize chance of
superheated liquids boiling over).
3. Open cooker and CAREFULLY remove flask of hot media. Agar should be
dissolved and in a layer at the bottom. Swirl flask to mix. Allow to cool
with occasional swirling.
4. While it is cooling you can prepare a clean countertop to pour plates.
Heroic sanitation isn't required, but it should be clean. Unwrap sterile
petri dishes and place (upright) in a stack on the counter.
5. When the flask has cooled to the point that you can just stand to touch
it from the outside, it is ready to pour. Should it begin to harden, you
can re-melt it in a pot of hot water. As long as it hasn't been opened,
additional pressure cooking isn't required for re-melted agar.
6. Holding the flask with a clean towel, remove the foil and begin to
pour the plates. Set the foil "hat" rightside up on the counter, so that
the inside surface remains essentially sterile.
7. To pour a plate, lift the lid with one hand and hold it while pouring
with the other hand. Immediately replace the lid. Bubbles aren't a big
problem, but they can often be removed by careful swirling of the molten
agar. Work quickly, keeping the flask and the insides of plates exposed to
the air for as little time as possible. I find it easiest to pour in
small stacks (placing an empty plate on top of the last plate poured)
rather than spreading them out over the counter.
If you need to interrupt the process for any reason, replace the foil cap
on the flask. As long as you avoid touching the inside of the plates or
the mouth of the flask, you should have no problem with contamination.
6. Leave the plates to cool on the counter until solid. Overnight is ok,
if they won't be disturbed.
Good luck. This should work. There is no need to be exceptionally
paranoid about sanitation when pouring plates, as contamination becomes
quite obvious within a couple days at room temperature. Then all you have
lost is a plate, which is a lot easier to part with than a batch of beer.
Steve Daughhetee
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End of Lambic Digest
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