Re: [Cider Workshop] Acidity, pH and titratable acidity.
dennis...@comcast.net
----- Original Message -----
From: "Andrew Lea" <y...@cider.org.uk>
To: cider-w...@googlegroups.com
Sent: Saturday, November 20, 2010 11:36:29 PM
Subject: Re: [Cider Workshop] Acidity
You have absolutely got it, James!! No more confusion now!
Your little essay should be required reading for anyone who puzzles
about it in the future!
Andrew
On 21/11/2010 00:42, James Fidell wrote:
>
> Having been out to the workshop to finish this evening's YM pressing and
> then spent a happy half hour surfing wikipedia, I think I am getting to
> grips with this...
>
> Malic acid is, as far as I can see, a "weak organic acid". "Weak" acids
> are ones that don't completely dissociate into their ionic forms in
> solution, but remain partially in molecular form. Each weak acid has
> it's own equilibrium point about which the dissociation balances, known
> as the acid dissociation constant, which is basically the proportion of
> acid in molecular form to that in ionic form.
>
> pH is a measure of the concentration of H+ ions in a solution, but in
> the case of weak acids some of the potential H+ ions are still tied up
> in molecular form so unlike the situation for "strong" acids which
> become completely ionic in solution, measuring pH doesn't give you an
> indication of the total amount of acid in the solution. Perhaps if you
> knew the dissociation constant for the acid it could be calculated, but
> if you had a mixture of several acids in unknown proportions then you
> look to be on a loser.
>
> I *think* titratable acidity is measured by introducing a base, often
> sodium hydroxide, to the solution. NaOH dissociates in solution to form
> Na+ and OH- ions, and the OH- ions combine with the H+ ions from the
> malic acid to form water molecules. I assume the Na+ combines with the
> remainder of the malic acid molecule to form a salt, sodium malate,
> (also known as E350 :). As a result of this, the molecular malic acid
> rebalances at its dissociation constant by forming more ions from some
> of the remaining molecules. Adding more NaOH reacts with those, causing
> further rebalancing and you keep going until the solution has a neutral
> pH (ie there are no more H+ ions created because you've run out of malic
> acid molecules to create them from). At that point, knowing the amount
> of base added allows you to calculate the amount of acid in the original
> sample.
>
> But not quite. In a simple solution that may well be the case, but
> where there are many different compounds present in a solution it may
> not be possible to know exactly what reactions are taking place and to
> what extent. So, in the general case the amount of acid measured by
> titration may well not be the same as the total amount of acid in the
> sample.
>
> I think that's it. It seems to be consistent and logical, so until
> someone points out any hideous flaws I shall use it as a working
> hypothesis.
>
> James
>
--
You received this message because you are subscribed to the Google Groups "Cider Workshop" group.
To post to this group, send email to cider-w...@googlegroups.com.
To unsubscribe from this group, send email to cider-worksho...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/cider-workshop?hl=en.
Andrew Lea
> This short essay is very helpful especially for relatively new cider
> makers like me. However, I still don't understand the relationship
> between "titratable acid" and tannins, a diverse group of phenolics
> that affect taste and astringency.
Oh dear. That is a very considerable confusion indeed, I'm afraid,
Dennis. There is NO relationship at all between titratable acid and
tannins. They are two quite different things.
> Andrew's article http://www.cider.org.uk/tannin.htm provides a great
> deal of information, but it does not explain why tannin levels are
> expressed in units of titratable acid as % of gallic acid equivalent.
>
It isn't and you have added a phrase that I never wrote! It is true
that tannin / phenolic levels when assayed by the Folin method are
conventionally expressed in "gallic acid equivalents" but that is
because gallic acid is a standard phenol, which also by chance happens
to bear an acid group. Titratable acid doesn't come into it; you are
being confused by the name "gallic acid" (which is structurally an acid
but a very weak one, in the same way that say ascorbic acid aka Vitamin
C is). Gallic acid is the stuff you can get from oak galls (hence its
name) and is a widespread plant polyphenol which is easy to crystallise
and purify in a lab. That's why it's often used as a standard. Its
acidic properties are not significant or relevant here - that's just
part of its name.
I hope that makes it clearer.
> TreeTop, a major supplier of unfermented cider in WA State, told me
> the tannin level in their cider were 200-450 mg gallic acid
> equivalent/ liter,
That is roughly what we would expect in US commercial apple juice (Motts
is around the same) and about ten times lower than the values from a
bittersweet cider apple.
Andrew
--
Wittenham Hill Cider Pages
www.cider.org.uk
Vigneron Rowland
> That is roughly what we would expect in US commercial apple juice (Motts
> is around the same) and about ten times lower than the values from a
> bittersweet cider apple.
>
> Andrew
you Andrew, this goes for everyone in the whole world, but especially
anyone who claims to love apples and cider. MOTT'S IS NOT APPLE
JUICE!!!! Although they are allowed to call it "juice," it is not.
Juice is the liquid squeezed or pressed from the fruit, in this case
apples. Mott's is what Michael Pollan refers to as an "edible food-
like product," made mostly from water, corn syrup, added acidity, and
some apple flavored concentrate, filtered clear and shelf-stabilized.
It is no different than what the English call "squash," concentrate
mixed down at home. And you wouldnt confuse squash with real juice
would you. "Juice" in US terms means "cider" in UK terms, and Mott's
isnt cider. Mott's (and all the products like it, Ocean Spray,
Welches, Tropicana etc ...) are at best apple "drink," non carbonated
soft drinks. To my knowledge there is no major or national brand of
real apple juice/cider in the US (although I wouldnt be surprised is
the UK product was different from that in the US because they can get
away with a crappier product here cause Americans dont care what they
eat as long as it tastes good). The US dairy industry protected
itself from this kind of fraud long ago, fake cheese must be sold as
"cheese-product" or "cheese-food" and fake butter must be labeled
"spread" (but again, that dosnt stop people from confusing them and
eating them). I hope the apple industry will adopt similar
protections from imitation products. sorry for the rant Andrew, but
I've got naught but passion and cider in my veins!
Vigneron Rowland
> That is roughly what we would expect in US commercial apple juice (Motts
> is around the same) and about ten times lower than the values from a
> bittersweet cider apple.
>
> Andrew
Vigneron Rowland
> isnt cider.
Nat West
... To my knowledge there is no major or national brand ofreal apple juice/cider in the US ...
dennis...@comcast.net
dennis...@comcast.net
Vigneron:
You may be correct about Motts but TreeTop insists their unfermented cider is made from apple juice concentrate and water with no additives or sugar. It is pasteurized however. They blend the concentrates to maintain an OG of 1.050 and a pH of 3.8. but the tannin level is very low. While I share your high regard for Pollan's advice and his books not all companies that sell "apple juice" adulterate the product they sell in the way that Motts does. The core problem is the US Department of Agriculture is controlled by the processed food industry and no longer has the best health interests of the US consumers in mind. Futher evidence that we have the best government that special interests can buy.
But the local growers of fresh pressed apple cider in the NW corner of Washington State don't help matters by a complete lack of uniformity and poor sanitation. I have discovered the OG and pH of their cider varies widely from gallon to gallon and the UV sanitation system they use doesn't control bacteria or yeasts very well. The growers claim UV processing does kill bovine e-coli but I am skeptical. I have had several batches of fresh cider spoil from contamination even when bought the cider off their filling line in the morning and pitched live yeast that afternoon.
Dennis
Andrew Lea
> all companies that sell "apple juice" adulterate the product they sell
> in the way that Motts does.
I bit my tongue the first time but I can't let this pass again. I used
to work for Motts at Williamson NY when it was owned by
Cadbury-Schweppes. I've seen the whole juice process through from fruit
to finished product and I can't agree with your analyses. Yes they do
also use concentrate and filtration and pasteurisation in their process
but that is common to most of the apple juice industry worldwide and has
been since the 1930's. It's not the same as US 'fresh apple cider' but
it doesn't claim to be. Motts 100% juice is not adulterated; there are
other products in their range which are juice drinks but those are
clearly labelled.