Concentrations
What percentage is your lactic acid?
"Lulz"
Usually when you read references from Japan, you’ll see (x) mL or Lactic Acid per 100 L of water. The standard concentration in Japan is actually 75% lactic acid* (source). But, if you go to buy lactic acid in your local homebrew shop, on amazon, or even in commercial suppliers, that concentration will typically be 88%.
If you put too much in, it could either drastically change the flavor, or if you don’t put enough, it could actually lead to a contamination. Maybe on the homebrew scale this isn’t as much of an issue, but on a large scale, that could be off quite substantially.
Let’s go over how to convert from one concentration to another so you add the correct amount.
* a member of the discord contributed a source (副原料 ・副材料,武蔵野化学研究所, 田中義暉, 乳酸のできるまで - link) which actually corrected this and explained the origins of why its’s commonly written 75%, but is actually 90%. Essentially, “when 90% lactic acid is directly titrated, the total value of free lactic acid and half of lactyl lactic acid shows a concentration of about 72%. A concentration of 90% total acid can only be obtained by adding excess alkali and measuring the concentration by back titration to determine the alkali consumption.” Other sources: (Acidimetric Titration and Composition of Commercial Lactic Acid. R. Eder and F. Kutter. (Heh. Chim. Acta, 1926, 9, 557-578.)-Commercial - link) and (Quantitative analysis of total acidity in aqueous lactic acid solutions by direct potentiometric titration - link)
(The math below is still valid, but would apply to 75%, not 90%, so if you happen to get a different concentration you can still use this, but from 88% to 90% you’ll probably encounter percentage of error before you notice a huge difference in flavor. Happy brewing!)
Do the Math
It takes 0.82 Liters (1.0 kilogram) of 75% lactic acid to raise the total acidity of 1000 Liters of water by 1.0% (source: 清酒製造技術, 公益財団法人 日本醸造協会, 2016, pg 270 ). So, we have that information, but now we need to know how much we should use if we only have 88%.
To determine this you can use the following formula:
C₁ × V₁ = C₂ × V₂
Where:
C₁ is the initial concentration (75%)
V₁ is the initial volume (0.82L)
C₂ is the final concentration (88%)
V₂ is the final volume or amount you want to find
Let's substitute the values:
75% × 0.82L = 88% × V₂L
Now, solve for V₂:
V₂ = (75% × 0.82 liters) / 88%
V₂ ≈ 0.699 Liters
So, you would need approximately 0.699 Liters of 88% lactic acid into 1000L of water to achieve the same concentration as 0.82 Liters of 75% lactic acid.
Properties of 100% Lactic Acid: source
But, what if want to ensure my accuracy and just weigh the lactic acid instead? After all, it’s difficult to judge volume in a graduated cylinder.
We can do some simple multiplication to figure this one out. Let’s take the density of lactic acid at room temp 20-25°C, which is 1.21 g/mL and multiply it by our volume (0.699L or 699mL)
M₈₈ = mass of 699ml of 88% lactic acid
M₈₈ = 699mL * 1.21 g/mL
M₈₈ ≈ 845.6 g (or 0.845kg)
If we weight out 845.6 grams of 88% lactic acid and add it to 1L of water, it should raise the total acidity by 1.0%.
Congratulations! We’ve done it!
Now, all of this is math has been about raising the acidity by 1.0%. But unfortunately that doesn’t mean that if we measured the acidity of our water after mixing it in that we would measure 1.0%. That’s because we haven’t considered was is already in the water.
It’s not something you can just say “I put in (X) mL of 88% lactic acid, so the pH should be exactly (Y)!”. And now we’ve entered the complicated crossover territory of Acidity vs pH level.
Many of these complications fall under that topic of water chemistry, and we’ll follow up on this a lot more in future posts. But incase you need to get started sooner, we’ve put together some calculators for you if you really want to start messing with this, but we warned… it’s a lot to learn and most people end up going with “close enough”.
Water Chemistry
The math involved in water chemistry is not easy. Unless you have taken the requisite chemistry classes to understand all the aspects of what is happening at a molecular level, you will probably not end up with what you want.
Take a look at the Sake Water Addition Calculator that one of our contributors, Reade Huddleston, put together for us. For help with it, check out this youtube tutorial.
You may already be familiar with the Bru’n Water calculator. Another contributor did a walkthrough of that tool for using it with Sake, as it is typically used for beer and that has a very different set of targets and other things to lookout for.
Check out our other posts for more advanced topics.
