A pH buffer consists of a weak acid and a conjugate base, for example citric acid and sodium citrate.
However, you do not necessarily have to use a conjugate base. Instead, you can use a strong base such as sodium hydroxide. This is because the conjugate base sodium citrate is formed from the reaction with the citric acid. If the quantities are calculated correctly, this is then the same as if you had taken sodium citrate directly.
A buffer not only sets a certain pH value, but it also provides a certain resistance to changes in pH. This resistance is called buffer capacity. This can be defined in different ways. You can enter two different buffer capacities here or have them calculated:

1. The general buffer capacity means how many millimol/lt H⁺ (i.e. dissociated acid) can be added until the pH has dropped by the entered tolerated value. Dissociated means that the acid is not only dissolved but also split into ions. Only the portion of an acid that is dissociated is effective. This degree of dissociation is also the reason why some acids are strong and others weak. But it also depends on pH: the lower the pH, the weaker the dissociation. How exactly depends on which acid we are talking about.
2. The buffer capacity in terms of g/lt acetic acid means how many g/lt acetic acid can be produced by the fermentation until the pH has dropped by the tolerated value entered. Here, the total amount of acetic acid is meant, not only the dissociated acetic acid.

We had still considered a buffer capacity related to g/lt dissolved CO₂. However, the results of the calculations showed that at the usual low pH values of our mashes, the CO₂ does not play a role. First, very little of the CO₂ produced dissolves, most of it escaping from the mash, second, very little of it forms carbonic acid (H₂CO₃), and third, very little of it dissociates at low pH because carbonic acid is a weak acid. Bubbled water therefore has a pH of over 5, well above that of fermenting mashes. We measured this, not calculated it.
In practice, the general buffer capacity depends not only on the amount of base or buffer but also, and above all, on the pH: The lower the pH, the more additional acid may be added without the pH dropping too much. Therefore, a buffer for low pH needs less ingredients in total than one for high pH. At least if the buffer is to act against additional acids, as is always the case in our fermentations.
For a better practical understanding, it should be mentioned that if you have an unfermented mash with pH 4 and add a buffer calculated for this mash volume for pH 3.5, you will not have a pH somewhere between 3.5 and 4, but one just below 3.5. The acids, which are responsible for the pH 4, thus push the adjusted pH 3.5 down a bit. And later, the acids produced during fermentation are there as well. We are only concerned with buffering against pH that is too low. Buffering against high pH is not necessary. This is because no bases are formed during fermentation, only acids.
How far you want to tolerate the pH reduction can be entered into the calculator. A general buffer capacity of 1 should actually be adequate for our purposes. It roughly means that the desired pH range is maintained if the pH of the mash would end up at 3 after fermentation without any buffering. If one fears that the pH will drop to 2 on its own, one would need a general buffering capacity of 10. If you only fear a drop to pH 4, a general buffer capacity of 0.1 would be sufficient.
Here an example:
Suppose you want to ferment 10 liters of mash between pH 3.5 and 3.2 and make the buffer from anhydrous citric acid and sodium hydroxide: If one does not expect the pH to drop below 3 without a buffer, a general buffer capacity of 1 is sufficient. With 3.5 desired pH, 1 general buffer capacity with tolerated lowering of pH by 0.3 (3.5 - 3.2 = 0.3), 7g citric acid and 1g sodium hydroxide are calculated.
Since pH 3.2 - 3.5 is probably what the yeast wants, this should work. It does not work if you want an unusually high pH for the yeast. Because practice shows that if you set the pH too high, the yeast itself will push the pH down. Too high here does not mean too high for the yeast but so high that its competitors benefit. Most bacteria cannot tolerate such a low pH as the yeast. Therefore, the yeast goes to great lengths to get the pH low, which means it produces more acetic acid from sugar and thus less alcohol. This behavior of the yeast reduces the practical value of this calculator. This is because the buffering capacity needed depends largely on how far away you want the pH to be from what the yeast wants. But it may be interesting to use the calculator to estimate how much acetic acid is produced, for example, if you want to artificially ferment a rum mash at a high pH. It is true that acids other than acetic acid are also produced, but firstly in much smaller quantities and secondly these other acids (for example butyric acid) are also weak acids, so behave similarly to acetic acid.
Thus, buffers with high pH and buffer capacities selected very high for safety are not recommended in normal cases.
In addition, moreover, because these would lead to very unnaturally high levels of sodium or potassium, which could affect the yeast.
The chemicals should be stored in a dry and closed place. On the one hand, many chemicals are hygroscopic, i.e. they absorb water from the air. Secondly, some substances react with the CO₂ from the air, for example the strong sodium hydroxide to the weaker sodium hydrogen carbonate. If there is a problem with absorbed water, however, the powder will also look wet. If, on the other hand, there is a problem with the CO₂, then you don't see it.
Citric acid is cheap, tasteless and efficient for different pH ranges. However, the yeast can degrade it over time. For us, this is not really a problem, as we do not store our washes for long.
Nevertheless, some people like to use the more expensive lactic acid, which is not completely neutral in taste even in the distillate, but this is not necessarily considered a disadvantage.
Buffers with malic acid, tartaric acid and ascorbic acid can also be calculated here. Malic acid is somewhat more expensive than citric acid, but quite economical in terms of the quantities needed, and is used, for example, in products such as Biogen M. Tartaric acid can be used, but it is not worth buying it extra. A buffer of ascorbic acid is even less economical.
We have not included phosphoric acid in the calculator. This would only be economical for very acidic buffers (pH 3 or lower). So for a buffer in our typical pH ranges, you would need a lot of phosphoric acid and a lot of the base for a reasonable buffer capacity.
Which bases you can use for buffers depends very much on their solubility in water. However, it is not enough for the bases to be soluble on their own; the salt formed with the acid and the carbonate formed with the CO₂ produced during fermentation must both be soluble, otherwise they precipitate and the buffer loses its effect. Then you have a lower pH than you calculated.
We have therefore not included the compounds calcium hydroxide and calcium carbonate, which are cheap to obtain, in the calculator. This is a pity, because calcium compounds are generally better for yeast than the other possible compounds. Nevertheless, it is possible to produce buffers with calcium compounds. However, you need quite high amounts for this and you cannot calculate them but have to check the pH regularly.
Also because of problems with solubility, we did not include magnesium compounds such as magnesium hydroxide in the calculator.
Therefore, only the very economical sodium compounds and the somewhat less economical potassium compounds remain. Sodium is theoretically worse for the yeast than potassium. Whether that is noticeable in the final product at our required levels is rather unlikely. But in any case, that's why someone might want to use potassium hydroxide rather than sodium hydroxide.
The buffer should be dissolved in a little water before adding it to the mash. It is best to dissolve the acid first and then slowly stir in the base. Because when the solution is acidic, the base dissolves better.
The yeast should be added to the mash only after buffering.