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Cider Digest #1213
Subject: Cider Digest #1213, 8 April 2005
From: cider-request@talisman.com
Cider Digest #1213 8 April 2005
Forum for Discussion of Cider Issues
Dick Dunn, Digest Janitor
Contents:
pH meters etc (Alistair Bell)
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Subject: pH meters etc
From: Alistair Bell <albell@shaw.ca>
Date: Tue, 05 Apr 2005 21:09:22 -0700
I have some working knowledge about pH meters, been using them for
years (my job in fermentation, bacterial that is, pilot plant stuff),
both bench models and the in-situ probes on the fermentor vessels.
I use, pretty well exclusively, glass electrodes, the old standard
type. They fermentor probes are made by the Swiss company Ingold. Quite
expensive, around $600 per. They are surprisingly durable (if you don't
whack them), and stay calibrated through sterility cycles (121C, 45
min) and prolonged culture use (conditions range from pH 3.0 @ 76 C to
9.0 @ 10 C).
The electrolyte used in these probes is simply a KCl solution, 3.0 M
(Ingold does sell a proprietary formula called Viscolyte, a modified
KCl solution). 3.0 M KCl is pretty much saturated solution, so is easy
to have some on hand to replenish probe.
Calibrating is done using pH standard solutions, pH 4.0, 7.0, and 10.0,
using the pH 7.0 and whatever other one that is in the range of
expected pH environment to be measured. Around pH 7 it doesn't matter,
but for cider I would use the pH 4.0 and pH 7.o standards.
The probe is immersed in the 7 standard to start and the pH amplifier
potentiometer is adjusted so that the meter reads 7. The probe is then
rinsed and immersed in the other standard, lets say 4.0. Then the
"slope" or mV potentiometer on the amplifier is adjusted to read 4.0.
Rinse and back to the 7.0, adjust, then back to the 4.0 and so on until
the 2 readings are correct.
So then we have the accurate zero point (7.0) and the slope (using the
4.0).
Some probes are gel electrolyte filled and do not require adjusting.
They are just tossed out when ever they get inaccurate. Some of the
current gel probes are very durable and one can get many "runs" out of
them.
But I still like the old type. When the probe becomes sluggish to
respond or drifts, or can be calibrated I can:
-flush out the electrolyte and replenish.
- -clean the little teeny ceramic diaphragm near end of probe with a
cleaning solution (HCl and thiocarbimide soln)
- -clean the end of the probe, the glass "membrane" with HCl - pepsin
solution to remove proteins etc
- - and if all else fail, clean the membrane with a dilute HF solution
that exposes fresh glass.
I like being able to resurrect these good old probes.
Bench meters are the same, for calibration and probe choices. I have a
neat little (just a little bigger than a cig package) unit made by
Beckman (no longer sadly), that has a clear LCD display, 2 pt
calibration, provision for temp compensation, and a "hold" feature,
that is the display fixes the pH reading when the readings settle down.
It really would be the cat's pyjamas for home use.
Meters are so much easier to use than pH papers, although i do use the
latter sometimes. If one can find an old meter, even an old analogue
(classic gauge and needle), with or without a probe, it would be smart
to pick it up. Probes can be bought for a range of prices. pH standard
solutions are cheap and available.
A new development in the pH measuring world are the silicon chip
probes. All solid state, no electrolyte etc. Expensive but look very
promising. If there are any wealthy investor types on the list contact
me for my notion of how to make money from this technology :)
Alistair
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End of Cider Digest #1213
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