SO2 Additions, again and again

[sietch]

Hi All,

Currently in the process of making my SO2 additions to my first batch of mead (15 litres, Traditional, 71-b, FG 1.031, pH 3.40).

I've been using k-meta with the Wine Maker Mag sulfite calculator and testing using a Vinmetrica SC-100A Analyser.

However, over the course of many days I've now probably added x4 the original recommend SO2 dose from the calculator…is this normal for a trad mead like this? I know adding an extra 33-50% is normal, maybe double for the first addition, but x4 times the amount?!

Very much aware SO2 can bind, however, after each addition, I waited 24hrs, then tested with the analyzer and every time have come up significantly short. After x4 additions (0.4g-0.6g per addition) I'm now finally at 14ppm Free SO2. The calculator says I need 24ppm.

Should I keep adding more or do you think this is an abnormal amount of extra SO2 to add and I’ve effed up somewhere along the line?

This is my first batch so I really don't have a frame of reference.

I made my first addition after racking off the lees with the mead decently clear.

Any input would be greatly appreciated. Cheers!

 

[joe.vinciguerra]

(40ppm may be more appropriate in this case because you have so much residual sugar, but that aside...)

Assuming you're using powdered potassium metabisulfite (k-meta), and not campden or something, there could be a few things going on aside from what you already mentioned:

1) k-meta degrades over time in storage. i.e. if it's old (don't ask me for specific times), it is less potent.

2) Is your scale right? Get some appropriately sized calibration weights for your scale and check that it's calibrated. As when I weigh things like this I do it multiple times: put it on the scale and get the amount you want, then remove it from the scale and weight it again. Does it repeat?

3) The vinemtrica reagents degrade over time. Like the k-meta, they have some shelf life.

4) Is your SC-100 calibrated? I don't believe Vinmetrica even mentions this, but any measurement device should be calibrated regularly. Shame on me for never calibrating mine.

After calibrating your scale, if you make a known solution of distilled water and k-meta to target your free SO2 (24ppm in this case; you want to calibrate in your operating range), then titrate as you normally would. If the results are correct (within a few ppm), then you know your scale, meter, electrode, reagents, and k-meta are all in good working order and it must me being bonded or dissipated in your mead more than expected. If not, then start replacing these consumables one at a time to find the weak link.

 

[joe.vinciguerra]

...Also, how quickly you titrate will affect the measurement results, among other things.