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Written by Stan Gower   
Friday, 20 November 2009 21:30

PMS, SO2 

PMS has a number of uses in wine making. 

1.     Used for sterilizing equipment, in a solution, at a concentration equivalent to 2 - 3 teaspoons in 5 litres of clean water. Thoroughly wet already cleaned equipment for at least 5 minutes, and drain, if residual PMS is not a problem; or rinse with clean water to remove all traces of PMS. 

2.     In the crush, to kill wild yeast, in the concentration equivalent of : -

-           0.535 g PMS / 10 kgs of grapes (1/14 of ¼ oz.)

  (ref. p 40 Red NMIT book) 

  1.    To help preserve the wine in making, and to help prevent oxidation of the wine when it is in contact with air. 

 Summary of additions, and maintenance levels of SO2, in RED wine. 

In the following guide, PMS (SO2) is added 3 times: - 

  1. At / before crushing. 
  2. After malolactic fermentation has finished before 1st racking. 
  3. Immediately after 3rd racking. 

      OPERATION

                          DETAILS

    AT CRUSH

 

 1. The 4 X rule for adding PMS

-           *100ppm PMS    

-             gives  50ppm total SO2

                    -      gives  25ppm  free  SO2    

 For 10kgs weight of grapes at crush, (This is the capacity of the manual crusher used here.)

 Call the amount *10 litres of juice for the purpose of calculating 50ppm total SO2; 25ppm free SO2.

(Do NOT use only the projected juice yield which would be around 5 litres from a 10kg crusher full of grapes.)

This is because about 50% of the SO2 will permeate the gross pulp stems and skins, and will be discarded at pressing, and some will be consumed protecting the juice during crushing and de-stemming and pressing, (and, for reference, in the yeast lees at racking.) and all the rest will be bound to aldehydes in the ferment

2.     CALCULATION of PMS amount.

       Quantity of PMS as for *10 litres juice.

        =*100ppm PMS               

1ppm =1mg per litre (1mg =1/1000 gm)

 So 100ppm =   100 mgs   per    1 litre

                    = 1000 mgs per 10 litres

                    =  1gm

So 1 gm PMS per 10 kgs of grapes

     at crush gives 50ppm TOTAL SO2,

      = 25ppm FREE SO2

  ______________________________________

 Weighing with a cheap balance.

 NOTE. My balance has a minimum of ¼ oz, and I really do not want to spend money at this stage on a better one. So:-

*1gms = 1/30 oz= approx 1/7 of 1/4 oz

             Or one level teaspoon is about 5 g

          The reasons for using 25ppm free SO2 at

          crush. = 100ppm PMS.

    (a) that is sufficient to protect the wine from                  oxidation during crushing then it is  protected by CO2  until the wine is pressed and MLF is completed.

    (b) because there must be no free SO2 for MLF to happen, and (up to) 25ppm free SO2 is bound during ferment.

  IMPORTANT. After adding 25ppm free SO2 at crush, do not add any more PMS until just before the first racking, after yeast ferment, pressing, and MLF are all completed.

 

     At 1st RACKING

 

1.       Send sample to laboratory to test for completion of MLF. (an addition of PMS will stop malolactic fermentation.) 

2.    then add 60ppm total SO2 = 30ppm free SO2 = 120ppm PMS.

Note. dissolve the measured PMS in water and stir it in.

 3.   No need to analyse for SO2 at this stage – about half of the addition will be free and will protect your wine at 1st, 2nd, and 3rd racking

See note at 3rd racking below.

 

    At 2nd RACKING

 

No further addition of PMS should be required provided previous additions were made as above.

 

 

    At 3rd RACKING

 

1 . There is no need to send a sample to have the SO2 measured before the 3rd racking.

 2. It’s a good idea at the third racking to take extra precautions against oxidation by purging the receiving containers with CO2 gas before racking.

 3. immediately after 3rd racking send samples for analysis for SO2 to work out the amount of PMS to be added, so that any PMS addition alleviates any oxidation from the   racking; and integrates well before bottling.

 Note ;  Alleviates means that Added SO2 will react with any dissolved oxygen picked up in the racking before it has a chance to oxidise the wine phenolics (turning them brown).

 This uses the SO2 as curative as well as a  preventative against oxidation.      .    

 

Removal of excess SO2 

            If you need to reduce the amount of SO2, (PMS) in the wine, for example, if there is too much to allow malolactic “fermentation” to happen, then SO2 can be reduced by adding hydrogen peroxide in a very carefully controlled amount. So you really need to get advice on how to prepare the amount to be used relative to each size container. 

            The hydrogen peroxide solution is added drop by drop, at room temperature, directly into the wine, and stirred in thoroughly as each drop or few drops are added. Temperature is not important.
Last Updated on Friday, 18 December 2009 09:44