Recipe 3: Melomel of elderberries with star anise (continued 2) -addition of yeast nutrients

It is day 3 since I started recipe 3 and it is time to do the third addition of yeast nutrition.

I have tried to get DAP (di-ammonium hydrogen phosphate) but no luck. So I came up with an alternative which in effect results in exactly the same addition. 

I did get my hands on MAP (mono-ammonium di-hydrogen phosphate) and I could of cause spike with twice as much (on mole basis) to add the same amount of ammonium ions. But that would also mean adding a large amount of phosphate which I am not so keen on. So as an alternative, I figured I would mix MAP with ammonium bicarbonate ("MAC") in the ratio 3:2 (by mass) and I would have added the same. Here is why

(NH4)HPO4 + (NH4)HCO3 -> 2 NH4+ + HPO4- + HCO3-

Since the must is about pH 4, HCO3- becomes H2CO3 = H2O + CO2 so in effect the addition is equivalent to the addition of DAP

And I learned something new. Ammonium bicarbonate is just a basic baking additive called "hjortetaksalt" here in Denmark - as you might have guessed I am not exactly the baking expert in the family :o)

On the web I can find several sites stating that for a high gravity must you need about 300 ppm of YAN (yeast assimilated nitrogen). You will also find the term FAN (free amino nitrogen) which is a constituent of YAN. DAP, MAP and MAC are all FAN components

To calculate how much to use you need to know the percentage by mass of nitrogen in each component of the addition. These are: 

Ferment K: 13% N (from table)

MAP: 12% N (calculated)

MAC: 18% N (calculated)

The reason why DAP is the preferred additive is that it contains 21% nitrogen by mass, so you have to add less to get the same FAN content.

Now since the molecular weight of MAP is 115 g/mol and MAC is 79 g/mol, these should be added in a ratio of about 3:2 to have the same composition as that of DAP. So if you add 3.0 g of MAP and 2.0 g of MAC it corresponds to adding about 3.5 g of DAP. The mass difference between adding DAP or MAP/MAC [(3.0+2.0) - 3.5 = 1.5 g] is in effect just CO2 and water.

So today I added:

3.0 g of MAP x 12% = 0.37 g YAN

2.0 g of MAC x 18% = 0.35 g YAN

2.0 g of Ferment K x 13% = 0.26 g YAN

In total: about 0.98 g YAN to 8.5 L = 115 ppm

Initially I added 2.0 g Ferment K just after boiling and the following day another 3.0 g of Ferment K

5.0 g of Ferment K x 13% = 0.65 g YAN

to 8.5 L = 76 ppm

So all in all I have added a bit short of 200 ppm YAN. 

I also found that it is recommended not to added any nutrition once 1/3 of the sugar have been consumed. I measured the density initially to about 1.135 and today it is 1.088. I expect the fermentation to stop at 1.025, i.e. 1/3 of the fermentable suger should be at 1.098 which was probably yesterday.....hmm. This is why I do not want to add all 300 ppm. But I must say that the fermentation has been sped up a lot by these nutrition additions and I will definitely be doing this from now on

As a final remark I measured pH with strips before and after the additions. The pH was unchanged at around 4. At least that was as well as it could be determined in the highly colored must :o)