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November 26th, 2011 at 11:39 pm

Measuring your Sake – Part four: Amino San-do (アミノ酸度)

In part one I talked about how to measure the Nihonshu-do or Sake Meter Value (SMV) or your sake. In part two I covered how to measure the Arukoru bun (アルコール度数) or Alcohol percent by volume (%ABV). In part three I covered how to measure the sando or acidity of sake. In this part, part 4, I will cover how to measure the amino sando of your sake.

As is the case for measuring the sando, you will need some Sodium Hydroxide (NaOH) solution usually at a concentration of 0.1 Molarity (M), phenolphthalein, a small beaker to mix the sample and chemicals in, and a syringe to measure with. All of this can be purchased as a wine acid test kit. In addition you will need some formalin[1] solution. As is the case in measuring sando, you can use the phenolphthalein as an indicator or a pH meter to determine the point at which the pH reaches 8.2.

The method used to measure the amino sando is very similar to the method for measuring sando. In fact, it incorporates the sando method as the first step in measuring the amino sando. This is because amino sando is just a specialized acid that is locked up and hidden in the structure. To measure the amino sando we must first remove or neutralize other acids so that they are not counted along with the amino acids. This is accomplished in the first titration step which determines the amount of base require to neutralize the acid. After our sample solution has been neutralized there are no more extra H+ to worry about and we can focus on how to make the amino acids visible, or at least measurable in some fashion. This is done with a formalin solution. The formalin solution reacts with the amino acid freeing an H+ from each amino acid structure. This free H+ can then be locked up using a base just as we did to measure the acid levels. So, one more round of titration using our base solution, sodium hydroxide (NaOH) will give us the level of base needed to neutralize the newly exposed acid so we can calculate the amount of amino acid as glycin, the simplest amino acid.

If that seems a bit intimidating, don’t worry, we will take it step by step from here.

OK, first we need to measure out 10ml of sample sake to evaluate. Place this in a beaker and add a few drops of phenolphthalein. The drops are not needed if you will use a pH meter. Load the syringe with about 10ml of NaOH and record the exact amount in the syringe for later reference; call it R1.

At this point, it is time to add, drop by drop the NaOH from the syringe to the sample watching for the indicator to change color to a light ping for at least 30 seconds. Swirl the sample after each drop as you go. If on the other hand you are using a pH meter you should gently stir the sample with the meter probe to get a correct reading. Once the color changes and holds its light pink color for at least 30 seconds you have neutralized the sample. Record the NaOH level now present in the syringe; call it R2. The difference between this and the earlier recorded level, (R1-R2) can be used to determine the sando (acidity).

Up until this point the procedure has been the same as measuring the sando. It is at this point that we depart from the sando method. Set the neutralized sample aside for use once we have a mixture based on the formalin ready.

Mix 50ml of formalin with 50ml of distilled water. Using the same titration procedure, neutralize the mixture at a pH of 8.2 or where the indicator turns light pink for at least 30 seconds. Remember to add several drops of phenolphthalein if you are using the indicator. There is no need to record the amount of NaOH used for this procedure.

OK, we are ready for the final step. Measure 10ml of the neutralized sample and 10ml of the neutralized formalin mixture and place in a beaker for a total of 20ml. Reload the syringe with NaOH and record the amount contained; call it R3. If you have been using phenolphthalein there should be enough present without any addition. Titrate this 20ml sample until it reaches neutrality at pH of 8.2 or until the color changes to a light pink for at least 30 seconds. Record the final level of NaOH in the syringe; call it R4. The difference between this and the previous recording will be the amount of NaOH required to neutralize the amino acid; (R3-R4).

Having completed all the measurements, it’s time to calculate the levels. First, as before for sando:

TA(g/L) = MoleRatio* (BaseMolarity * BaseVolume * MoleMass) / SampleVolume

=>

Sando = TA(succinic g/L) = ½ * (0.1M*(R1-R2)ml*118) / 10ml

And similarly for amino acid:

TA(g/L) = MoleRatio* (BaseMolarity * BaseVolume * MoleMass) / SampleVolume

=>

Amino Sando = TA(glycin g/L) = 1 * (0.1M * (R3-R4)ml * 75) / 20ml

Where the BaseMolarity is the concentration (moles / liter) of NaHO in distilled water, BaseVolume and SampleVolute are the amounts of NaHO and Sample solutions in ml.

Succinic acid, along with malic and lactic acid are the most abundant acids in sake. As discussed in part three, succinic acid has a reaction ratio, MoleRatio, with NaOH of 1:2 giving rise to the ½ in the Sando equation. The amino acid glycin reacts with NaOH in a 1:1 reaction giving rise to the multiplier 1 in the Amino Sando equation.

The molecular mass (MoleMass)of succinic acid is 118 while the molecular mass of glycin is 75. As you see, these have been substituted in the equations above.

Using a pH meter can be slower and more tedious than using phenolphthalein but the pH meter will be more accurate. In either case, any amount that you are off on any of the titration steps, first for sando, second for formalin or the final step for amino sando, will throw off the following step or be thrown off by the previous steps; that is, the error will accumulate with each step.

Another thing that should be understood and kept in mind when working with NaOH is that its concentration will change over time. NaOH reacts with CO2 in the air neutralizing its base character.  You can use Hydrochloric acid (HCl) to determine the strength of the NaOH solution. HCl is stable so, while NaOH is changing, HCl will remain constant and able to measure the new/ current strength of the NaOH concentration using the same titration methods used above. Maybe I will discuss this in more detail in a future article. [12-10-11, well I added a post on this. You will find it here]

Well, there you have it, the procedure to measure the sando and amino sando of your sake.



[1] Formalin is a saturated solution of formaldehyde at 40% by volume or 37% by mass.

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