Recommended free SO2 level

[Chiumanfu]

I have a RJS EP Pinot Grigio that I'm ready to bottle. The pH is 3.05. The winemaker calculator is telling me that I should be at 25mg/L free SO2. Most of the charts out there suggest around 15mg/L free SO2 to achieve 0.8mg/L molecular SO2.

The winemaking calc is consistently about 10ppm higher than the charts for any given pH value.

What value should I go with?

 

[ffemt128]

The app I have on my tablet say you need 24.7 ppm for a white at that ph.

 

[Turock]

Yep--I agree with the 25 PPM using .8 mol as a target.

 

[ibglowin]

There are some charts with 0.4mg/L and that would be for reds since tannin acts as an antioxidant. Most people just use the 0.8mg/L to be safe. Perhaps your looking at a chart with the .4mg/L?

Otherwise that 25mg/L sounds spot on for that pH

 

[Turock]

I think .4 mol is a little low. I've always read that .5 to 1.5 mol could be appropriate depending on color, level of tannin,alcohol, and residual sugar. .8 mol covers just about all dry and red wines.

 

[Chiumanfu]

The charts I am referring to are:

http://www.winemakingtalk.com/forum/f86/recommended-level-od-so2-charts-36645/#post403800

http://www.brsquared.org/wine/Articles/SO2/SO2.htm

http://vinmetrica.com/sulfite-adjustments-what-to-do-with-my-so2-results/

http://morewinemaking.com/public/pdf/so2.pdf

They all say I need around 15mg/L free SO2. Am I reading the charts wrong? I would like to minimize SO2 but not at the expense of long term ageing.

 

[Runningwolf]

Honestly I never liked the charts myself. I go strictly by the winemakers calculator. I sometimes even go over by 10 ppm depending on where I'm at in the process.

 

[Chiumanfu]

Played around with the winemaker Calc a little bit more. It give the correct value if I select "red wine" in the drop down box... even though my Desired Molecular SO2 value doesn't change. Maybe the calculator just pads on an extra 10mg/L when you chose white wine.

 

[Runningwolf]

Play with it some more. It will change between red or whites. Change it then click in another box.

 

[Chiumanfu]

Thanks Dan but I still can't figure it out.

Select "Red", set 0.8mg/L, set pH 3.05, and the "Recommended Level of Free SO2" is correct (according to the charts and formulas around the net) at 15mg/L.

Select "White" , set 0.8mg/L, set pH 3.05, and the "Recommended Level of Free SO2" is 25mg/L. The "Desired molecular SO2" does not change from 0.8 therefore the Recommended level should really not be changing.

If I plug in 25mg/L into the formula to find Molecular SO2, I get...

Molecular SO2 = Free SO2/(10^(pH-1.81)+1)
Molecular SO2 = 1.36mg/L
That's quite a bit higher than where I'd like to be.

It's like the calculator is changing the formula when you change between white and red but it doesn't correctly take into account the value you enter in "Desired Molecular SO2".

In any case, I wrote a small excel file to do my calcs. I just load it onto my Google Drive and access it from my phone/ipad whenever I need. I've attached it incase others may find it useful.

View attachment Wine SO2.zip

 

[Runningwolf]

ok this calculator is kind of finiky sometimes. I tried what you said you did and got the same results. Go back to this calculator and enter the white wine first and you'll get 25ppm. I have this saved to my desktop and sometimes I have to close it out and start over again fresh.

 

[Chiumanfu]

Somebody please tell me if I'm wrong but... I've run through the math a hundred times, cross referenced all the formulae, check and double checked... and I've come to the conclusion that the winemaker mag SO2 calculator is consistently wrong when you set the drop down box to white wine.

When you select "Red Wine", the formula is unchanged.
When you select "White Wine", the formula simply adds 10mg/L to the "Recommended Level of SO2" in the notes section.

Not sure why the author decided that a simple 10mg/L addition is ok, but it is misleading and the error is magnified in high acidity wines where a difference of 10ppm is actually quite large. For example, say I have a white wine with a pH of 3.01 and my Desired Molecular SO2 is 0.8mg/L. Enter that info into the WM calc and it says I need 23mg/L free SO2. If I go ahead and raise my total free SO2 to 23mg/L, my Molecular SO2 will not be 0.8mg/L, it will actually be 1.37mg/L. That is substantially higher than I wanted.

Solution is to leave the wine type as "red" no matter what you are testing and set the "Desired molecular SO2" to the value that corresponds to your wine type. ie 0.6 for reds and 0.8 for whites... or 0.8 for everything if you like keeping it simple.

 

[wineman2013]

The problem is that this is a kit .
It's hard to get a true ph reading on a kit because they are so heavily buffered.

I would follow their instructions . Email them or since both you and Rjs are in Vancouver , give them a call . They will help you out.

With most kits that's use the kmeta provided and another 1/4 tsp at bottleing.

Grape winemaking protocols don't always apply.

 

[ibglowin]

I have never had a problem obtaining a "true" pH reading on a kit wine. The pH is stable as a rock, doesn't drift more than a few hundreds of a pH at most.

Now fresh grapes you bet. Especially if they have been grown in a hot climate and they are loaded with Potassium. Especially immediately after crushing when your trying to get your initial numbers. You will definitely see a pH drift on something like that.

It's hard to get a true ph reading on a kit because they are so heavily buffered.