Will Potassium Metabisulfite prevent store-bought Grape Juice from fermenting?

Question

There's a store-bought grape juice that I'm interested in lacto-fermenting (i.e. no yeast, only bacteria, anaerobic ferment, etc) but I recently discovered Potassium Metabisulfite is added to "enhance freshness."

Will potassium metabisulfite prevent me from lacto-fermenting this grape juice?

Another thread has given me insight into how much potassium metabisulfite stops fermentation but since the amount is determined by the manufacturer, the amount of potassium metabisulfite that stops fermentation seems like a moot point since I don't know the amount being used.

Thanks for your help in advance.

Answer 1

While I am no expert on this topic, I did a little bit of research to help you out. It is generally understood that in winemaking metabisulphite inhibits bacteria and yeast growth, so I would think that this could cause a problem for you.

This topic has been discussed on winemakingtalk and there is a consensus near the bottom of the thread where H2O2 (hydrogen peroxide) can be added, in addition to aeration of the juice. The post specifically references section 11.2.1 of Improved Winemaking where an analysis is presented on how to neutralize SO2. Section 15.3 specifically discusses using H2O2 and provides some example calculations.

The first step would be finding out just how much metabisulphite is actually in your juice in order to neutralize it. Perhaps the juice provider can give you an idea, or there may be industry standards.

I will quote the poster "gordini" from his post on winemakingtalk in case the forum ever disappears:

Free SO2 can be removed by adding hydrogen peroxide (H2O2) to wine. The use of H2O2 is considered too severe by many. Nevertheless, it remains one of the only real options for removing excessively high levels of SO2 from wine for the non-commercial winemaker.

Make up your solution and add it very slowly while stirring, even wait a few hours in between additions because more SO2 comes out of solution at each treatment,until an equilibrium is reached.

From section 15.3 of Improved Winemaking

Solutions of H2O2 commonly come as 3% solutions. If they are mass/mass solutions (this appears to be the typical case) they should contain about 30.3 mg/ml H2O2. If they are volume/volume solutions they should contain about 42.3 mg/ml H2O2. (See "Information on H2O2 content" below for more details.)

So... in the following 1 mg/l is the equivalent of 1 ppm.

15 litres of wine has a free SO2 level of 70 mg/l. It is desired to reduce this to 40 mg/l. The reduction of 30 mg/l (70-40) requires an H2O2 addition of 16 mg/l (0.5304*30). Thus, the 15 litres requires an addition of 240 mg (15*16) of H2O2. Using a 3% mass/mass solution of H2O2, 7.9 ml (240/30.3) of the solution needs to be added to the 15 litres for the drop to 40 mg/l.

I hope this proves useful. Investigating it has been educational for me too!

EDIT: I took a stab at the math here, and, well, I hope someone will check it for me. First, I've assumed you want to reduce your free SO2 to 0 which is probably not realistic. To do so theoretically you would need to at 1.952L H2O2 to your 1.89 gallon of juice which, well, you won't have much juice left. I'm not sure what the minimum amount left you want is - that would take some research.

I've uploaded my work and would appreciate a review from someone just to check. There's probably a reason people buy juice for winemaking instead of using juice with sulphites, and maybe this is it?

Answer 2

Yes.

Potassium Metabisulfite works by depleting oxygen to inhibit aerobic growth. It doesn't "kill" yeast or bacteria in the short term.

Potassium Metabisulfite can be defeated by adding a lot of oxygen. In my experience shaking or a stirplate alone is not enough. It needs a very good dose of pure oxygen much more than what you would add to beer to get yeast started. Add oxygen every few hours until noticable fermentation starts.