Re: How is gas produced when different foods are crushed and added to vinegar?

Hello, Texas.

You have noticed the production and/or release of gas when adding vinegar 
to different foods.  I discussed this question with my mentor from years 
ago, Dr. GD Brown, and we came up with a number of possible explanations 
for this but, for now, I will just go into the two most probable and how 
you can verify these.

1)  Carbonates are frequently used as processing aids to help retain color 
    in canned/frozen vegetables.  Because they are processing aids, they   
    often don't have to be stated in the ingredient declaration which you  
    no doubt checked for clues as to what is reacting here.  

    When the vinegar is added, any residual carbonates (bases)would react  
    and produce CO2.

    Confirmation: Add the vinegar to the food and cap the bottle right away 
    (glass jar, metal lid).  Then, if you can access a headspace gas       
    analyzer(or some area lab SHOULD volunteer to do this for your class), 
    puncture the lid with the analyzer.  If the gas being produced is CO2, 
    then this acid-base reaction is likely the explanation.

    Just take precautions not to let an excessive amount of gas build up - 
    glass jars have been known to break from the pressure.

2)  I think that the most probable explanation for this observation        
    originates with the procedures used in the production of vinegar.

    Most of our white vinegar comes from the fermentation of sugar.  When 
    things ferment there is lots of bubbling and foaming, so it is common  
    practice to use anti-foaming agents to eliminate this.  Food grade    
    anti-foams, another undeclared processing aid, are usually silicones.  
    When you add the vinegar to the crushed food, the still-functioning, 
    residual anti-foam causes the release of dissolved air.

    Confirmation:  Before adding it to the food, neutralize the vinegar to 
    pH 7 with dilute NaOH - again using standard precautions.  Observe 
    closely as you add the vinegar to the food.  If there is gas     
    production, it is due to the presence of the anti-foaming agent & has  
    no connection to the acidity of the vinegar.


Carol Crouse
The Food Chain Ltd.
New Brunswick, Canada
ccrouse@nbnet.nb.ca