Spherification - sodium citrate pecentages in relation to acidity?

[Rockchef]

Hi all,

I’m trying to source information on the pH of various fruits with a
view to establishing where sodium citrate may be required as an
acidity buffer for spherifications.

Has anyone any information they would like to share?

If you have a fruit spherification recipe that has required sodium
citrate and would like to post the required % for the selected fruit
then that may be a starting point that I could then hopefully collate
with the fruit pH value.

Ideally I would like to establish a guideline formula for the required
percentages of sodium citrate in relation to acidity.

Thanks in advance.

[Martin Lersch]

> Ideally I would like to establish a guideline formula for the required
> percentages of sodium citrate in relation to acidity.

You would want to keep the pH > 3.65 to avoid precipitation of alginic
acid. One way to achieve this is to buy pH strips and aim for let's
say pH 5 by addition of tri sodium citrate. If the fruit has a
starting pH of 2, you need to add about 2.6 g tri sodium citrate pr.
liter of liquid to reach pH 5. If the juice is at pH 3, you only need
0.26 g/L. However, if you add 2.6g/L to something at pH 3.5 it will
only take you up to pH 6.9. This could influence flavor, but will not
ruin the spherification or the texture.

The following pH values might serve as a reference:
lemon juice pH 2.4
vinegar pH 3
orange juice, apple juice, red wine etc.are all about pH 3.5.

For an extensive list, check out:
http://vm.cfsan.fda.gov/~comm/lacf-phs.html

Too make a long story short: If you have something really acidic use
something like 2.6 g/L. If it's not that acidic, use a fraction of
this.

If you want to play around with the buffer calculations, try this
page: http://dbr.csoft.net/chem/bufcalc.php

Cheers,

Martin

--
Martin Lersch, Ph.D.

Website dedicated to molecular gastronomy
http://blog.khymos.org
http://khymos.org

[Rockchef]

Great ..Thank you for the information & links – very helpful.

Just to check I am on the right lines.. am I correct in the assumption
that the sodium citrate requirements will reduce by a division of 10
for each unit decrease in acidity?
& can I evenly divide the points between i.e. will a product with a pH
of 2.5 require 1.43gm ? or is the formula more complex..

Thanks again…this info is much appreciated!

[Martin Lersch]

> & can I evenly divide the points between i.e. will a product with a pH
> of 2.5 require 1.43gm ? or is the formula more complex..

No. It's a little more complex...

Starting pH Tri sodium citrate to add, g/L
2 2.68
2.5 0.845
3 0.265
3.5 0.082

Cheers,

Martin

--
Martin Lersch, Ph.D.

Website dedicated to molecular gastronomy
http://blog.khymos.org
http://khymos.org