I am looking to calculate the percentage acidity of different drinks for the purposes of devising cocktail recipes. According to Liquid Intelligence by David Arnold, the optimum acidity level is 0.7-0.9, based on analysis of classic cocktails. How might I calculate the acidity percentage level of say lemonade (pH 2.9)?
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2$\begingroup$ What is percentage acidity and acidity level? Note that there is no direct relation between pH values and acid content. There are factors as acidity constants of phosphoric or carbonic acid or organic acids like citric or tartaric ones. and related pH buffer system presence. $\endgroup$– PoutnikNov 2, 2022 at 16:18
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$\begingroup$ Good question - I was hoping someone could help clarify. In this cocktail calculator> cocktailchemistrylab.com/calculator < you can see that different ingredients are given different percentage acidities when you enter them into 'ingredients'. This is the approach used in the above book by D Arnold. $\endgroup$– Dr StuNov 2, 2022 at 16:53
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1$\begingroup$ I like to say this in similar context: A asking B, why C said X, does not usually provide a satisfactory answer. As B does not usually know why C did so either. A should ask C. $\endgroup$– PoutnikNov 2, 2022 at 17:19
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$\begingroup$ pH calculations assume absence of other solvents like ethanol. $\endgroup$– PoutnikNov 2, 2022 at 17:23
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$\begingroup$ I doubt your "percentage acidity" or optimum acidity level, whatever it's supposed to be, has much to do with pH, or even chemistry altogether. Taste is an abstract created by human mind. $\endgroup$– MithoronNov 2, 2022 at 17:43
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1 Answer
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After looking at the link you posted, it seems "% acidity" refers to the mass percentage of citric acid in lemon juice, which is approximately 6%.
The percent acidity of your lemonade will depend on the percentage of lemon juice that constitutes it.
Let:
$X_{J/L}$ = the mass fraction of lemon juice in lemonade.
$X_{C/J}$ = the mass fraction of citric acid in lemon juice.
$m_{C/L}$ = mass of citric acid in lemonade
$m_L$ = total mass of lemonade
If you know how much water and lemon juice constitutes your lemonade, you can calculate "percent acidity" with:
$$m_L\;X_{J/L}\;X_{C/J}=m_{C/L}$$
Solving for $X_{C/J}$:
$$X_{C/J}=\frac{m_{C/L}}{m_L\;X_{J/L}}$$
Which is equivalent to:
$$X_{C/J}=\frac{X_{C/L}}{X_{J/L}}$$
Finally, solving for $X_{C/L}$:
$$X_{C/L}=X_{C/J}\;X_{J/L}$$
For example, if you mix 150g of lemon juice with 850g of water, the total mass of the mixture will be 1000g, and ${X_{J/L}}$=0.15, ${X_{C/J}}$=0.06
So "%acidity" for your lemonade would be:
$$X_{C/L}=X_{J/L}\;X_{C/J}=(0.15)(0.06)=0.009$$
Which is 0.9 percent.
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1$\begingroup$ Please familiarize yourself with Which symbols are written in roman (upright) font and which are italicized? and note that the unit symbol is separated from the numerical value with a non-breaking space (i.e. use
\pumacro provided by mhchem). "Mass fraction" is also the better term than "mass percentage". $\endgroup$– andselisk ♦Nov 7, 2022 at 16:10 -
$\begingroup$ Thanks for your observations and link. I will try to keep them in mind for my next post. $\endgroup$– Sam202Nov 7, 2022 at 16:34