SO2 standard
Ken
I have just got my SO2 "Rankine" aspiration apparatus together and set up
and have started playing around with it. The method I am working from
suggests calibrating the apparatus with a "standard 50ppm SO2 solution",
mostly to ensure that the aspiration rate is correct.
Am I right in assuming that a "standard 50ppm SO2 solution" is NOT a 50ppm
solution of metabisulphite in water?
My guess is that it is likely to be a solution of metabisulphite in water
where 1 mole of metabisulphite generates 2 moles of free SO2 on
acidification with phosphoric acid?
If that assumption is correct, my calculation is that 50ppm SO2 is the
equivalent of an 86.7ppm solution of potassium metabisulphite. The
calculation is ((222/(64*2)) * 50) where 222 is the MW of K2S2O5 and 64 is
the MW of SO2.
Any comments on my chemistry assumptions and my calculations would be much
appreciated as well as comments on using this particular method for SO2
determinations in red grape wines.
Regards.....Ken
Tom S
"Ken" <kena...@ozemail.remove.for.valid.email.com.au> wrote in message
news:k3RR9.184$oM1....@nnrp1.ozemail.com.au...
> To all the wine chemists out there....
>
> I have just got my SO2 "Rankine" aspiration apparatus together and set up
> and have started playing around with it.
I'm glad to see this topic. I have some red wines that I need to know the
free SO2 of, but was contemplating either sending out the stuff to a lab or
figuring out how to do the vacuum aspiration analysis myself. PIA either
way, but I can't see the color change well enough using the standard Ripper
on red wines.
> The method I am working from
> suggests calibrating the apparatus with a "standard 50ppm SO2 solution",
> mostly to ensure that the aspiration rate is correct.
>
> Am I right in assuming that a "standard 50ppm SO2 solution" is NOT a 50ppm
> solution of metabisulphite in water?
Correct. You can measure out meta that way, but you must remember that it's
only 57% _maximum_ available SO2. I recently became aware of how reactive
that stuff (K2S2O5, aka "meta") is - even in the dry form. I had some wine
that I'd calculated to be ~40ppm free SO2, but when I titrated it against a
fresh iodine standard turned out to be only ~10ppm free.
> My guess is that it is likely to be a solution of metabisulphite in water
> where 1 mole of metabisulphite generates 2 moles of free SO2 on
> acidification with phosphoric acid?
On acidification. Period. Below pH 2 or so, it's essentially all free.
> If that assumption is correct, my calculation is that 50ppm SO2 is the
> equivalent of an 86.7ppm solution of potassium metabisulphite.
Heinz 57 makes it easy to remember the percentage of available SO2 from pure
meta.
> Any comments on my chemistry assumptions and my calculations would be much
> appreciated as well as comments on using this particular method for SO2
> determinations in red grape wines.
So, Ken. Please fill us in on the rigorous details of doing vacuum
aspiration measurements of the free and total SO2 in wine. Most of us have
no clue how vacuum aspiration is done, so some practical advice and dialogue
on this topic would be informative and appreciated.
(I can contribute that your SO2 standard should be titrated freshly against
a thiosulfate standard, which is more stable but which should also be
relatively fresh.)
Your calculations appear to yield the right results, but remembering all
that detail is unnecessary for most practical winery operations. Just
remember that 3.9 grams of K2S2O5 added to a 60 gallon barrel will increase
the SO2 by 10ppm. You can also use 17.5 mg/liter or 1/3 gram/5 gallons =
10ppm. You can scale those pretty easily for most applications. Just pick
the one that you can most easily remember and use. My 2¢ worth...
Tom S
Joe Sallustio
I use titrettes and watch the color of the foam that develops for
reds, it's easier to see that change than the wine sample for me. I'm
very interested in the vacuum aspiration method too but am just not
motivated enough to do it at this point...
Regards,
Joe
"Tom S" <dont_sp...@pacbell.net> wrote in message news:<NLSR9.6170$ec1.30...@newssvr14.news.prodigy.com>...
Ken
thanks for your input and interest.
I was glad to see that your "Heinz 57" value equalled my 86.7ppm calculation
arrived at independently ;-)
For those that are interested, the reason I ventured into home SO2 testing
was threefold:
- the cost of getting someone else to do it (about 1/20th the cost of the
setup per sample)
- being from a scientific background, the interest in having some control
over the quality of the result
- I had just the place for it in the winery lab (my domain under the house)
and it was the chance for a new toy after all.
I did a bit of research into the methodology which is really quite simple. A
fixed volume of wine is acidified by the addition of 25% phosphoric acid.
That acidification acts to liberate free SO2 gas from the wine sample and
that is driven or drawn through a solution of hydrogen peroxide in which it
converts to sulphuric acid. The apparatus is left bubbling away for 10 to 15
minutes to allow the reactions to go to completion. With the use of a
burette and a coloured indicator in the peroxide, the sulphuric acid is back
titrated with a known concentration of sodium hydroxide. The amount of
sodium hydroxide used translates into a free SO2 concentration in the wine
by simple multiplication. The process can then be repeated with boiling of
the acidified wine to get a total SO2 concentration but, so far, I haven't
toyed with that, I'm mostly interested in "free".
There are two types of apparatus, one from the school of "sucking" and the
other from the school of "spitting". I have posted diagrams of both types on
my web site http://www.mitchelhill.com/so2.htm for anyone interested. By
"sucking and spitting" I refer to whether the air stream is drawn through
the apparatus by vacuum (a water pump in most cases) or pushed through the
apparatus by positive pressure (a fish tank pump in most cases). I opted for
the latter since it looked simpler, meaning it would cost less. The
"spitter" does have the advantage of having a fixed flow rate for each test
(once it is calibrated) although positive pressure in quickfit style
apparatus is fraught with the chance of leaks. The "sucker" on the
otherhand, won't leak but will require fairly constant attention to the air
flow rate.
These apparatus are expensive things off the shelf when sold complete
(A$600) but the local labs charge A$30 per sample for a proper red wine SO2
so, in the scheme of things, it will pay for itself over a few vintages. I
payed a bit less for my gear by going to a scientific glassblower with the
drawings, funny ... when things aren't labelled "wine" they suddenly cost a
lot less ... why is that?
So, after a few sessions at the apparatus, it is very simple to use and very
reproducible and I'm glad I made the investment. I am currently basing my
results on the calculations assuming my solutions are the correct, I would
love to have a way to independently verify them, the issue of calibration
that I haven't quite solved. It sounds theoretically simple to make up a
stock potassium metabisulphite solution but, as you alluded, the powder we
all have on our benches is not very pure and goes off quite quickly. I would
be interested to hear ideas as to how this can be calibrated by an
independent method (is Ripper quantitative when done in simple aqueous
solution?).
That's enough babble for now.....Ken
"Tom S" <dont_sp...@pacbell.net> wrote in message
news:NLSR9.6170$ec1.30...@newssvr14.news.prodigy.com...
>
David C Breeden
>Tom,
Hi Ken,
When I wanted to test our A/O apparatus, I made up a SO2 solution by
bubbling SO2 from a tank through a carboy of water, measured it's
density with an accurate hydrometer, and used the table in
Margalit's _Winery Technology and Operations_ to figure the
concentration of SO2.
That's only useful if you have access to pure SO2 gas, though.
Dave
****************************************************************************
Dave Breeden bre...@lightlink.com
Ken
now that's a very nice way of preparing a standard.
Did you just happen to have easy access to a bottle of SO2 gas or do you use
it in your regular winemaking practice?
What uses does SO2 gas (as opposed to metabisulphite) have around the winery
or is it simply a substitute? Does it have any advantages of metabisulphite?
Regards...Ken
"David C Breeden" <bre...@adore.lightlink.com> wrote in message
news:3e1ac57d$1...@news2.lightlink.com...
David C Breeden
>David,
>now that's a very nice way of preparing a standard.
>Did you just happen to have easy access to a bottle of SO2 gas or do you use
>it in your regular winemaking practice?
>What uses does SO2 gas (as opposed to metabisulphite) have around the winery
>or is it simply a substitute? Does it have any advantages of metabisulphite?
>Regards...Ken
HI Ken,
We use the solution in the carboy to add SO2 to all our wines.
The gas can also be used directly in barrels after washing, to
prepate them for dry storage.
Unknown
> > >These apparatus are expensive things off the shelf when sold complete
> > >(A$600) but the local labs charge A$30 per sample for a proper red wine
> SO2
> > >so, in the scheme of things, it will pay for itself over a few vintages.
(Sorry if this is double post. I don't see my original one, so gonna try again. Trying out a new browser.
still got some kinks, me thinks.)
That seems high even at the exchange rate. The basic labware for free SO2 can be found here in the states for
about US$160.
Here's a decent pdf file of the procedure:
http://vinquiry.com/pdf/so2freeaoQ.pdf
lots of other good info here, including total SO2 procedures:
http://vinquiry.com/reference.htm
clyde
Ken
yes, I have seen that website thanks, it didn't really add anything to the
information that I had, it doesn't talk about standardization at all and
that was the original point of my posting. As a biochemist, I hate any
methodology being promoted without due attention being paid to calibration
and controls.
With regard to the prices you quote, yes, that would be in line with the
price I paid to my scientific glassware supplier. The A$600 does include the
air pump and the burette for the final titration as well as all the
reagents, but, I agree, looks a bit pricey.
Regards....Ken
<Clyde> wrote in message news:1103_10...@news.misn.com...
Ed Marks
Can you direct me to where the labware can be found for that price.
Everything I've seen is closer to $400. I'd like to try the aeration
oxidation test, and $160 is a lot more reasonable.
Thanks,
Ed
<Clyde> wrote in message news:1103_10...@news.misn.com...
>
Tom S
> What uses does SO2 gas (as opposed to metabisulphite) have around the
winery
metabisulphite?
Using SO2 gas is the way big commercial wineries sulfite their wines. They
don't use metabisulfite - probably because of the cost and possibly because
of the uncertainty of the SO2 yield from the salt.
Tom S
Ken
that we need to replace our metabisulphite on a regular basis anyway?
Ken
"Tom S" <dont_sp...@pacbell.net> wrote in message
news:B08T9.1136$IM2.69...@newssvr21.news.prodigy.com...
Fred Williams
flask, a double hole stopper, some glass tube, some plastic tubing and a
test tube to accomplish a very accurate aspiration.
Use the plastic tubing to hook the air pump to one glass rod which extends
to very near the bottom of the flask. Connect a length of plastic tubing to
the second glass rod which should terminate near the bottom of the stopper.
Run the second plastic tube into the test tube near the bottom.
To use: add the peroxide and indicator to the test tube. Normalize the
test tube, then pour the sample into the flask. Quickly dump an equal
amount of acid into the flask. Immediately secure the stopper, and start
the air pump. bubble for about 15 min. and titrate.
"Ed Marks" <edm...@mindspring.com> wrote in message
news:256T9.794$jt4...@news.bellsouth.net...
Joe Sallustio
A good pressure regulator costs around $150; unless you can get that
cheap i doubt that will work out for you. Most bottles are presurized
to 2000 - 2500 PSIG as I recall.
Regards,
joe
"Ken" <k...@mitchelhill.no.junk.mail.com> wrote in message news:<avj46q$n9n$1...@ariel.ucs.unimelb.edu.au>...
David C Breeden
>Ken
>A good pressure regulator costs around $150; unless you can get that
>cheap i doubt that will work out for you. Most bottles are presurized
>to 2000 - 2500 PSIG as I recall.
>Regards,
>joe
Hi All,
I don't think you can use a normal regulator--SO2 gas is really,
really corrosive. I know I wouldn't want a tank of it stored at my
house, or even in my detached garage. It's just way too hazardous.
Ed Marks
Thanks - Ed
"Fred Williams" <nsf.wi...@verizon.net> wrote in message
news:0n9T9.11751$db.1...@nwrddc04.gnilink.net...
Ed Marks
Can you tell me about the pump you're using? My understanding is that you
need an airflow of about 1200ml/min. - the aquarium pumps I've seen seem to
be rated in gallons/hour - I think the correct equivalent is 20 gallons/hour
or 72L/hour - does that line up with what you're using? Thanks for your
help.
Ed
"Ken" <k...@mitchelhill.no.junk.mail.com> wrote in message
news:avdsgg$g2r$1...@ariel.ucs.unimelb.edu.au...
Ken
response to a request for prices, the costs for those interested (in $A,
multiply by 0.6 (approx) for $US)
27kg cylinder SO2 is $242.07
stainless steel type 32 cylinder connection, price $256.00
braided stainless steel teflon lined hose - an 800mm long version is $162.50
and then there is the cost of a sulphitometer which they couldn't tell me
about.
Quite an investment!
Ken
"David C Breeden" <bre...@adore.lightlink.com> wrote in message
news:3e1d5f26$1...@news2.lightlink.com...
Tom S
"Joe Sallustio" <joe_...@hotmail.com> wrote in message
news:91e0a179.03010...@posting.google.com...
> Ken
> A good pressure regulator costs around $150; unless you can get that
> cheap i doubt that will work out for you. Most bottles are presurized
> to 2000 - 2500 PSIG as I recall.
You're thinking of nitrogen or argon bottles. SO2 canisters or tanks are
pretty low pressure - probably lower than CO2 - sort of in the propane
ballpark. Most of the contents is in the liquid form (as with propane).
Regulators don't work well on them. A needle valve, to regulate the flow,
is better.
Actually _getting_ an SO2 cylinder is not as easy as it once was. They
won't let you just drive up and throw it into the trunk of your car anymore.
It's a major HAZMAT deal now, and the price has gone up dramatically from
when I bought 8lb cylinders for less than $30US. :^(
Tom S
Andrew L Drumm
winemaker. The last winery I worked at (100-250T) used PMS for general
sanitisation stuff and SO2 gas for additions to wine. The current one
(300T), with more wine in tanks (making SO2 gas additions even easier), uses
PMS only. We also have used effervescent SO2 tablets (similar to but not
quite campden tablets - these are much more carefully measured doses of SO2)
in barrels - the advantage of the effervescence is that you don't have to
stir the barrels - a difficult task when they are stacked on top of each
other. Addition of SO2 gas to large tanks can also be simpler with a good
diffuser, as you don't have to mix the tank so much.
However as pointed out elsewhere, a cylinder of SO2 gas is quite a hazard,
PMS being a safer option. The SO2 is not however under great pressure - not
much more than atmospheric is required to keep it liquid, and there is only
a needle valve on the outlet.
Cheers,
Andrew
_______
This message is to be read as an attempt to provide information. Where
possible I have attempted to indicate where this information came from. Any
errors etc are mine, but I will ignore nitpicking and outbursts of LIVID
ANTAGONISM in a similar manner to Gloria!
"Ken" <kena...@ozemail.remove.for.valid.email.com.au> wrote in message
news:R2RS9.131$Yy4....@nnrp1.ozemail.com.au...
David C Breeden
>I got an email from our local scientific gas supplier this morning in
>response to a request for prices, the costs for those interested (in $A,
>multiply by 0.6 (approx) for $US)
>27kg cylinder SO2 is $242.07
>stainless steel type 32 cylinder connection, price $256.00
>braided stainless steel teflon lined hose - an 800mm long version is $162.50
>and then there is the cost of a sulphitometer which they couldn't tell me
>about.
>Quite an investment!
>Ken
Hi Ken,
I think the sulfitometers are qutie pricey too, but you don't really
need one. And really, you don't need the ss tubing or even the
regulator.
What we used to do, and I'm sure it's NOT the recommended practice,
was to have teflon tubing (I think teflon, but I'm not sure) running from
the outlet of the tank into a 5 gal. carboy filled with water. The
valve on the tank was opened and closed by means of a pair of vice
grips. If you needed additional SO2 solution, you'd fill up a
carboy of water, run the hose into into it, and then just barely
crack the valve open, so you could see a stream of bubbles running
from the end of the hose.
This would be done as the last thing at night, so it could be left
overnight. It was done in a space that could be opened to the
outside without having to come inside first, so it could be
ventilated before entering.
We'd usually, if we had good control of the valve, get 7% SO2
solutions, or thereabouts. If I remember right, a saturated
solution is about 8-9%.
This is defintely NOT the best way to do it, but it works, and all
it costs is the SO2 tank, the teflon tubing, a carboy, and a pair of
vice grips.
Tom S
> What we used to do, and I'm sure it's NOT the recommended practice,
> was to have teflon tubing (I think teflon, but I'm not sure) running from
> the outlet of the tank into a 5 gal. carboy filled with water. The
> valve on the tank was opened and closed by means of a pair of vice
> grips. If you needed additional SO2 solution, you'd fill up a
> carboy of water, run the hose into into it, and then just barely
> crack the valve open, so you could see a stream of bubbles running
> from the end of the hose.
>
> This would be done as the last thing at night, so it could be left
> overnight. It was done in a space that could be opened to the
> outside without having to come inside first, so it could be
> ventilated before entering.
>
> We'd usually, if we had good control of the valve, get 7% SO2
> solutions, or thereabouts. If I remember right, a saturated
> solution is about 8-9%.
>
> This is defintely NOT the best way to do it, but it works, and all
> it costs is the SO2 tank, the teflon tubing, a carboy, and a pair of
> vice grips.
That's actually pretty standard practice, Dave, and the way I learned it
too. The water should be cold and ideally the stream of bubbles should
disappear before it hits the surface or you've got the flow going too fast
and are wasting gas. A narrow range hydrometer is used to measure the
concentration of the solution.
Tom S
Fred Williams
control valve between the pump and the flask to adjust the air flow.
Most any aquarium pump will put out too much air if the flow is
uncontrolled.
"Ed Marks" <edm...@mindspring.com> wrote in message
news:2NlT9.3798$jt4....@news.bellsouth.net...
Lum
I know of three small wineries down here in the southwest forty currently
using this procedure. Seems to work.
Regards,
lum
Clyde
> Clyde,
>
> Can you direct me to where the labware can be found for that price.
> Everything I've seen is closer to $400. I'd like to try the aeration
> oxidation test, and $160 is a lot more reasonable.
>
> Thanks,
>
> Ed
>
Ed,
If you ask Vinquiry to send you a dead tree catalogue, they have a free SO2
kit listed at the $160 I mentioned. It uses a water driven aspirator, with
the plastic version being rather reasonably priced. In my part of the
world, water is cheap and somewhat expendable. Your situation may be
different.
clyde
Ed Marks
Thanks Clyde - I'll check that out. By the way, in my part of the world (Atlanta) water has been in great abundance this year, so I can guiltlessly test away.
Ed
Clyde
river.
My comment comes from my stay in Central California where they were a bit
touchy if you flushed the toilet when it wasn't "absolutely necessary"!
clyde
Ken
sorry for the delay, have been away from home.
The pump is an Elite 800 Aquarium pump manufactured in Malaysia for a
company called Rolf C Hagen (UK) Pyt. Ltd. It delivers 1100ml/min at 1.4
psi. I think this is the equivalent to the Hagen Elite 799 in the US? See
http://www.hagen.com/usa/aquatic/product.cfm?CAT=1&SUBCAT=102&PROD_ID=010079
90020101
Given the textbook requirement for the test is 1000ml/min, it pretty much
does the job.
Regards....Ken
"Ed Marks" <edm...@mindspring.com> wrote in message
news:2NlT9.3798$jt4....@news.bellsouth.net...
RJR
> To all the wine chemists out there....
>
> I have just got my SO2 "Rankine" aspiration apparatus together and set up
> suggests calibrating the apparatus with a "standard 50ppm SO2 solution",
> mostly to ensure that the aspiration rate is correct.
>
> Am I right in assuming that a "standard 50ppm SO2 solution" is NOT a 50ppm
> solution of metabisulphite in water?
>
> where 1 mole of metabisulphite generates 2 moles of free SO2 on
> acidification with phosphoric acid?
>
> calculation is ((222/(64*2)) * 50) where 222 is the MW of K2S2O5 and 64 is
> the MW of SO2.
>
> Any comments on my chemistry assumptions and my calculations would be much
> appreciated as well as comments on using this particular method for SO2
> determinations in red grape wines.
>
Woah, that's some big math. It doesnt have to be so complicated. It
probably doesn't matter a whit what the strength of your solution is,
as long as YOU know and you can replicate that number or a reasonable
faximile of it on your apparatus consistantly. One gram of FRESH
k-meta in theory equals 150 ppm (actually just over, about 150.3...)in
a gallon of your favorite liquid. Fractions of grams are difficult to
measure accuratly so be careful, you have to trust your standard. I
suppose if you were willing to fork out for the apparatus you might
have a pretty cool scale too. The other issue is free/total so2.
Distilled water will bind essentially zero so2 (especially if you
acitify it a bit) so virtually all of it should come over as free. As
for total so2, who cares? You'll know it's reasonable (80-150 ppm), so
why waste
the reagents? (so you can keep them fresh by using them up) Have fun!
RJR
Tom S
> kit listed at the $160 I mentioned.
A _free_ SO2 kit for $160? Sounds like something by the Firesign Theater.
"It's free - just a dollar..." ;^D
Tom S
Ed Marks
Ed
"Ken" <kena...@ozemail.remove.for.valid.email.com.au> wrote in message
news:QwIT9.44$0j7....@nnrp1.ozemail.com.au...
Clyde
> > they have a free SO2
> > kit listed at the $160 I mentioned.
>
> A _free_ SO2 kit for $160? Sounds like something by the Firesign Theater.
> "It's free - just a dollar..." ;^D
>
> Tom S
>
>
AND IF YOU ORDER NOW......
PAYMENTS OF ONLY $19.99 A MONTH.
Looking at this again, it has to make you wonder (not about the Free part ;)
If you add up all the parts it does come to much more.... closer to the tune
of $300.
A winery that I work with nearby, purchased a bare bones unit from St. Louis
Wine and Beermaking for $188. It's listed on page 25 of this pdf file:
http://www.wineandbeermaking.com/TempImg/images/wineandbeermaking/catalog.pd
f
This does not have a flowmeter, but did include all the reagents and
glassware?! We will be sending samples to the state lab this week for
comparison.
clyde