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Cider Digest #1214
Subject: Cider Digest #1214, 12 April 2005
From: cider-request@talisman.com
Cider Digest #1214 12 April 2005
Forum for Discussion of Cider Issues
Dick Dunn, Digest Janitor
Contents:
PH meters ("Julian Temperley")
Alcohol determination by refractometry (Andrew Lea)
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Subject: PH meters
From: "Julian Temperley" <somcb@globalnet.co.uk>
Date: Sat, 9 Apr 2005 09:33:46 +0100
We make cider in Somerset , England. Years ago I brought a ph meter and
it was always a problem. For the last twenty years we have triturated
with iodine/starch to give us an acid level. In our case we are looking
for higher than .35. It is not the same as ph , but near enough ,
cheap, quick and fool proof. You can buy the chemicals from any wine
supplier. We use Vigo in the UK . Julian Temperley
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Subject: Alcohol determination by refractometry
From: Andrew Lea <andrew_lea@compuserve.com>
Date: Mon, 11 Apr 2005 21:40:29 +0100
Three of of us (Gary Awdey plus myself and Martin Harris in the UK) have
been looking at the possibilities for measuring alcohol in cider without
complex lab equipment. The official methods are direct GLC or
distillation followed by some direct measurement of alcohol in the
distillate such as density or refractometry - but neither of these can
be done in the back kitchen and require proper chemical lab facilities
or contract analysis at say $50 (£25) per sample.
One method used by small brewers is to measure the density of the beer
(by hydrometer) and its refractive index (by hand-held refractometer).
By plugging this data into a suitable set of equations (for instance,
those available via Promash - demo download from www.promash.com) it is
possible to compute the alcohol content. However, these equations make
certain assumptions about the materials other than ethanol which
contribute to SG and RI, and it turns out that they are pretty far out
for cider (under-reading by as much as 1% alcohol). Unfortunately it
seems that the refractometer manufacturers do not realize this and are
still offering 'beer' equations to wine and cider-makers (although I
await confirmation of this as a fact!)
As far as I know this SG/RI technique has never been validated for cider
and no accurate equations are available - so any cidermaker trying to
measure his alcohol level this way is shooting in the dark and may be
getting some pretty wrong results - we have some preliminary evidence
that this is the case. I have however found a number of literature refs
dating from the 1950's onwards to its use in grape wines. These are
summarised in a Slovenian paper which is freely available on the
internet at http://public.carnet.hr/ftbrfd/40-321.pdf These wine
equations give values about 0.6% ethanol higher than the beer equations,
and some preliminary data seems to indicate that they're much closer to
the 'true' alcohol value in dry cider than are the beer equations. So
far, so good. The fact is that no equations have been validated for
cider, and for instance the addition of simple cane sugar for sweetening
cider will throw the equations off balance once again.
My reason for posting is to raise awareness of the issue and to ask if
there's anyone out there who is currently using the SG/RI technique for
measuring alcohol in cider, what equations are they using to compute the
results, and how accurate is it compared to the 'official' methods of
alcohol measurement? Is anyone using alternative techniques such as an
ebulliometer with any success for alcohol measurements cider?
Andrew Lea
- --
Wittenham Hill Cider Page
http://www.cider.org.uk
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End of Cider Digest #1214
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