Titratable acid testing kit

[Bittersweet]

Has anyone any experience of using the following acidity testing kit?

Acid test kit VINOFERM complete
Brouwland catalogue number: 013.049.2

Would I be right in thinking that because it's a wine testing kit the
result is likely to be expressed as tartaric acid, but the kit should
just measure total acidity so multiplying by the appropriate
conversion factor (0.89) will yield a figure for total malic acid ?

[Claude Jolicoeur]

I didn't see the catalog (and am too lazy to make a search for it) but
if this kit is what I think, what you say is correct.
See my recent post on vinegar acidity testing to use such kits more
economically...
http://groups.google.com/group/cider-workshop/browse_frm/thread/1d48dd00acf3ce0e#
Claude

[Bittersweet]

How rude - forgot to add the link to Brouwland!

http://www.brouwland.com/en/

[CiderHead]

You've got me interested in this now. I've got a "Winemaster" test kit
and the instructions say that the result is ppt as Sulphuric Acid.
Should I be applying a conversion factor to get it to it's Malic Acid
equivalent?

[Andrew Lea]

Yes. You should be multiplying by 1.4

Andrew

--
Wittenham Hill Cider Pages
www.cider.org.uk

[Claude Jolicoeur]

Bittersweet wrote:
> How rude - forgot to add the link to Brouwland!
>
> http://www.brouwland.com/en/

Hum, this is different from what I use.
What I use is rather like this (and the indicator is red):
http://www.clickabrew.com/shopexd.asp?id=528
Claude

PS- note that in the Brouwland page, they do mention that the acidity
is expressed as tartaric acid.

[CiderHead]

Thanks for the information, Andrew. That's quite a difference.

[from Heather]

I just barely started using a wine acid test kit, and I realize now reading this thread that I've been applying it wrong. Part of my problem is that I don't completly understand the theory, but I am slated to take three week long "Chemistry for Winemakers" from my local college here in two weeks. Not that it would really help for cider, but it would get me more comfortable and familiar with everything. It would be nice to do Claude's method to save on materials, but I'm just not there yet.

Here is what I do, which I'm figuring out this morning isn't right. 

Per the kit instructions, which says, "the results are expressed as a percentage of tartaric acid":
15 cc apple juice
4 drops of phenolphthalein
Slowly add sodium hydroxide solution, .2N until it turns pink.

Now the instructions say that for every cc, it is .10% acidity. So 6 cc = .6% acidity. Thing is, % acidity is absolutely meaningless to me.

I've been using a formula from Peter Mitchell, which says that:
Malic acid (g/L) = volume of sodium hydroxide solution used (mL) x 0.536
Peter also mentioned that 5 g/L was sort of ideal.

In writing up this email, I'm not sure that I'm properly doing this as while the ingredients for the test are the same, the amounts are different. Peter calls for:
25 mL of juice (that's 10 cc more)
6 drops of phenophthalein (that's 2 more drops)
slowly add sodium hydroxide solution 0.2 mole 1(to the -1 power) until it turns pink

I guess I need to switch over my amounts used to match Peter. That's actually using more, not less like Claude.

Heather

[Claude Jolicoeur]

Heather wrote:
> I just barely started using a wine acid test kit, and I realize now reading this thread that I've been applying it wrong. Part of my problem is that I don't completly understand the theory, but I am slated to take three week long "Chemistry for Winemakers" from my local college here in two weeks. Not that it would really help for cider, but it would get me more comfortable and familiar with everything. It would be nice to do Claude's method to save on materials, but I'm just not there yet.

Heather,
I use 1.5 cc of juice, to which I add 1 drop of phenolphtalein.
Then I fill a 1cc syringe (the type used for insulin, with 0.1cc
graduations) with the base NaOH, which I introduce slowly. Then the
mixture turns pink-red, I look on the graduations on the syringe to
see how much NaOH I added. For example, if I used 0.6cc of NaOH, it
means the acidity of the juice is 0.6%, expressed as tartaric acid
equivalent, or 6 grams of acid per litre.

Now that you have this measure, you can use the 0.89 conversion factor
to have the TA expressed as malic acid equivalent.

So, Peter Mitchell's 5 grams per litre is 0.5% TA as malic acid,
divide by .89 gives 0.56% TA as tartaric acid.

Claude

[from Heather]

Ah, that seems easy enough to follow.

I have a technical question about the phenolphtalein in the test, but I'm sort of afraid to ask as it doesn't really matter to the the testing or my results, and it could possiblty confuse me, so I'm not really sure I want to know.

Thanks,
Heather


> Date: Thu, 14 Oct 2010 09:58:54 -0700
> Subject: [Cider Workshop] Re: Titratable acid testing kit
> From: cj...@gmc.ulaval.ca
> To: cider-w...@googlegroups.com

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[sparkybloke99]

if your question regards the effects of phenolphtalein on human
digestion rest assured if you dont use gloves or wash your hands
you'll soon find out!

[j...@jondenton.com]

I've read the books regarding storing fruit may be beneficial as it give
chance for more of the starch to turn into sugar, but what about acid ?

Some websites I've read suggest keeping high acid fruit till after
Christmas before pressing. I can only assume that the 'mellowing' effect
of storing dual purpose / cookers reduces the acid.

I'm a little concerned that my blend will be too acidic as a lot of the
donated / wildings I've come across seem to be acidic. I was going to test
the ph of the individuals this weekend but was interested if longer
storage would be of any benefit to ph levels.

Cheers

Jon