To raise pH I use pot ash or potassium carbonate (K2CO3). Potassium has no risk limit in foods because it is considered harmless and just as important, potassium does not impart a salty taste. CO3-- is on the other hand a quite strong base, and should be handled with care.
So, as titrator I used a 0.10 M K2CO3 solution (Mw 138.2g/mol) by dissolving 0.70 g in 50 ml of tap water using my old but trusted analytical scale and a 100 ml glass measuring cylinder. As titrand I used 40 ml of currant mead again measured with a 100 ml glass measuring cylinder
To add the titrator in a controlled fasion I used a 1 ml plastic syringe with needle. The needle provides a sufficiently small exit hole to control and "cut" small droplets. After each addition to the mead, I gave the solution a quick stir on my home made magnetic stirrer (ref HERE), and measured pH with my pH meter (ref HERE).
Adding in total 2 ml moved pH from 3.41 to 3.89. I found that adding 1.2 ml resulted in a pH of 3.70. Targeting this pH, I would likely be within the "sweet spot" with some error in the volumes used.
Converting the addition in ml to add K2CO3 in g to 1L the graph looks like this:
Some of the fluctuations from linearity might be due the various pKa values but with the general uncertainty of all numbers involved, I figured I could approximate the data as linear.
So, to get pH 3.7 I would need to add 0.42g K2CO3 to 1 L of currant mead. Since my batch size now is about 19 L I would need to add a total of 7.98 g. I have tested my scale with analytical reference weights and found it to be off by 6% and the error is proportional. Therefore I can just correct the target mass by 1.06 and I would need 7.53g K2CO3 and the actual mass will be 7.98g.
The entire amount was gently sprinkled into the fermenter and the entire volume was stirred well afterwards. I left the fermenter for 10 min to let the K2CO3 dissolve fully and mix with the mead. Then came the crutial check: Target 3.70 -> measured........
PERFECT !
No comments:
Post a Comment