pH meter

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tonyhibbett

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It seems that total acidity and pH are related, but not the same thing, (I don't really understand it) but getting both levels right dramatically improves both fermentation and flavour.
I was using a titration kit but found this fiddly and the chemicals work out fairly expensive if you do lots of testing. Also it gives the results in terms of sulphuric acid, which is none too helpful when you are actually dealing with tartaric and/or malic acid.
So I opted for litmus paper. I was unable to find narrow range papers so ended up with universal ones instead. While these were helpful and gave instant results from a tiny sample (eg a single grape) they could only tell me, at best, if I was in the desired range between pH 3 - 4, but the colours never quite matched those on the chart, and anyway colour, like taste, varies with individual perception. I have tracked down a digital pH meter on eBay for £9, which seems very reasonable compared to what I was led to expect, and which claims to be accurate within 0.1 pH. Hopefully this will take out much of the guesswork which has led to some wines (and cider) being marred due too crude an assessment of their acidity. Hopefully I will in time be able to match the effect on my palate with some specific data. Hopefully...
 
tonyhibbett said:
they could only tell me, at best, if I was in the desired range between pH 3 - 4, but the colours never quite matched those on the chart

I use those papers as well and it is always a struggle to match the color. I find myself running around to the apartment to test the color under each light within the apartment. My usage of those stripes is just to make sure that the PH level is high enough as I prefer it high. I considered getting a reader but I did not want to invest 20-30€ for that.
 
pH meters are very good, but I think you may have to pay £20+ for a reliable one.
Titration is the most accurate way of measuring acidity.
Sulphuric acid is used as the standard against which acidity is measured, it doesn't matter whether you are measuring Malic, Tartaric or citric acid.
The pH meter doesn't care what acid you are measuring either!
Total Acidity has a pH of 1, while total alkalinity has a pH of 14, thus neutrality has a pH of 7.
 
Sort of agreeing with Jim.

A good pH meter will cost you at least 70 quid, and in terms of winemaking will not give you what you need.

Take a solution of apple juice and titrate it and you may find that the acidity is 3.5ppt (sulphuric) . . .if you measure it's pH it could come out around 4.6

Now dilute it by 10 (ie add 9 parts of water) . . . titrate the acidity and you'll find that it is 0.35ppt . . . measure the pH however and you'll find that it is around 4.6!! :wha:

sulphuric acid was chosen as a standard to express the equivilance of various acids in the must.

10ppt sulphuric = 14.3ppt citric = 13.7ppt Malic = 15.3 tartric (from Acton and Duncan Progressive Winemaking)

They also give a couple of acid mixes that when used can add a known degree of acidity to the must.

The following chapter does give a way of determining the titrateable acidity of the must from the pH ( and vice versa) which although is usable (given a thorough knowledge of logs and the disassociation constants of the acids involved . . . and the algebra) they do finish off by saying

Acton And Duncan said:
Since the composition of wines and musts is extremely complex, it is clear that no satisfactory correlation can possibly be derived between pH and titrateable acidity of a must or wine. The concentration of acid is only one of the many factors which determine the pH under these conditions, so that the pH of a must or wine is merely the measure of its hydrogen ion concentration and no more.
<snip>
It certainly cannot be emphasised too strongly that the pH of a must or wine is best not employed as a measure of its acid content.
 
Aleman said:
Sort of agreeing with Jim.
I try my best, but as you know Tony, I don't get overly serious about the chemistry of Brewing, Vinting or Making.

Once set up with Burette, Retort stand etc, it is very cheap and simple to titrate with 0.1N Sodium Hydroxide for acid concentration.
The same equipment also determines the concentration of SO2, it's the normality of the Iodine that's a bit tricky.
My reference for SO2 is 10 CTs dissolved in 1 gallon of demineralised water, 100ml of this being made up to 1 litre = 50ppm.

I believe that accepted concentration of acid for white wine is 0.5 - 0.6% Sulphuric.
 
I have been using (in another field) pen type pH testers for over 10 years now . They started out £100 plus , then £60 and now you can buy a not-awful chinese one for around a tenner . So long as you rinse the sensor after use and 2 point calibrate often with buffer solution they compare well with the £100 jobs....in the short term . You gets what you pays for after all . Be sensible and dont expect the world for a tenner and they will do you fine .
 
tonyhibbett said:
So you can measure sulphur dioxide? I have searched in vain for an affordable so2 test kit. Please tell me more!

I've got something on doing this easily but it's in my bookmarks at work. If I remember I'll dig it out on monday.

May as well hijack the thread while I'm here. Would be interested in hearing model recommendations for a pH meter from Tony.
 
Meanwhile I tried the pH test by diluting wine with 10 parts distilled water. The test paper indicated the original pH 3, diluted pH 5. The pH numbers are, I believe, scaled by a factor of 10, ie 3 is 10 times more acidic than 4. Had I used 9 parts water, it's just possible the reading could have straddled either side of 3. Nonetheless, it certainly highlights the limitations of universal indicator papers and the need for greater precision, hence the meter, with a resolution of 0.1 pH. More news when it arrives!
They were still useful as a quick way of indicating a change in the acidity of the ripening grapes, from pH 3 to 4 from late september to late october, proving that the extra month made a very significant difference. However, the decision to pick was based on the fact that the sugar content was not changing. The final pressed juice actually had 7 ppt, way too high for dry white wine for my liking. Had I known november was going to be the warmest ever, things might have turned out better!
 
pH meter has arrived. Pen type. Battery included. So far, consistent with univerrsal papers, but far more precise. Distilled water (for cleaning) and buffer solutions (for recalibrating) not supplied.
Clearly I need to do lots of cross referencing between meter, papers, titration and mouth feel to derive truly meaningful data and also get some proper, narrow range papers.
Got the book 'Progressive Winemaking'. Both absorbing and daunting, especially concerning barrels and ageing. Also ordered 'Award Winning Wines ...' which should be more up to date.
 
It helps to store the pen upright with the cap filled with distilled water to keep the sensor wet , that and rinsing well after use which can be done under to tap as long as you finish with distilled . Otherwise you can get buildup of various stuff and the pen giving you false readings from dry . We used to reckon on leaving the pen in the liquid to be tested for up to 20 minutes to get a true reading and even then doing a series to compare and average .

As far as buffer solutions aquarium suppliers are good and the two part ones best , better even to do the 2 part , high and low numbers AND the pH 7 one .
 
Many thanks.
Basic tests with meter: Distilled water pH 6. Purified water 5.5. Tap water 7.5. Jug filtered 6.7. Aqua Pura mineral water 6.1 (as stated on bottle). So I guess it's accurate enough and probably needs no calibration, as yet.
First result: Dry cider. Universal paper, between 3 and 4; meter, 3.6; titration, 4.75 ppt. (as sulphuric). Acid test kit suggests 4.5 as max, unless high proportion of fruit used. In this case 100% pure apple juice, no water.
Taste, very good, with just enough bite.
Also bought cheap Boots blood glucose monitor. Test result for cider was e-7, too low to register. That's less than 0.05%. For £5, a useful gadget to objectively test true dryness only, as range is 0.05 to 0.3% glucose, although it does not detect any other residual sugars.
The SG was 0. Abv 5.5%.
 
Demand for the pH meter must be very low because I was sent 2 for the price of 1!
The water results were particularly interesting in their own right. When I had the water supply analysed, I was disturbed and have since used a jug filter for beverages and cooking purposes, but after reading 'Progressive Winemaking', I now regard my tap water in a slightly more positive light, being very rich in minerals which are very useful in fermentation (as well as undesirable contaminants), not that I'd ever drink the stuff neat again!
The book also gave me the idea for the blood glucose meter, although they seriously misinterpreted by a whole decimal point. Still, nice to know that I don't have diabetes, (like all good bio scientists, I tried it out on my own body first), unlike the cat, although the acid in my blood must be approaching that of 'Alien', as in the movie.
But if I am going to do all these titration tests, I will need vast amounts of 'standard' sodium hydroxide solution. My local 'chemist' is great for toothpaste, feminine hygene, prescriptions and useless cough medicine, but as a supplier of chemicals, is totally hopeless.
 
Mistral Cleaning Products and BioStain are two I have used that I remember , there are a couple more chemical suppliers that I can link you to if you want them .

I found sodium hydroxide easy to come by but nasty like most sodiums . Potassium Hydroxide is easy to come by from hydroponics suppliers ,some swimming pool and aquarium places too, and is a better bet , reckons I ...
 
Sodium hydroxide doesn't sound like the sort of thing you'd want to move in next door and marry your daughter, and anyway next door is not up for sale and they are both, so far, happily married anyway.
It proved difficult to get potassium carbonate because the Post Office consider anything potassium as a potentially explosive substance, and refuse to ship anything labelled as such. Yet having got a lifetime supply of the stuff, I am quite happy to put it into my wine to drag down the acidity and drink it.
I only want sodium hydroxide for acid testing purposes only.
 

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