The problem with these batches is yeast. Yeast is used in bread making, beer fermentation and, of course, Vegemite, the breakfast spread many New Zealanders were brought up on. So why is yeast dangerous?
Yeasts convert sugar to alcohol and carbon dioxide. They put the fizz in beers and sparkling wines. If this occurs in a controlled fermentation process, there is no problem. However, if yeasts get into finished products containing sugar, such as bottled fruit juices or alcoholic beverages with residual sugar (not fermented to "dryness"), they can produce carbon dioxide in the bottle. The cells can generate pressures up to 10 atmospheres - sufficient to burst the bottle.
The recall notice says:
- handle the bottles carefully, wearing gloves and protective eyewear, to determine if the product is from the affected batch
- on an individual bottle, the batch code is printed on the bottle’s neck
- on a 12-pack the batch code can be located on the long side of the pack, to the right of the barcode
I once saw a similar recall notice that effectively invited anyone having the affected product not to touch it, but to call the bomb squad!
This may sound a bit melodramatic, but think about this:
One of my winemaking colleagues wanted to produce sparkling wine from a batch of still wine. He calculated the amount of carbon dioxide to dissolve in the wine and added this to the bottles as small pellets of carbon dioxide ice. He put corks in the bottles and wired them on and then stored the bottles in a cupboard.
A few hours later, there was a tremendous bang from the cupboard. He found only the necks and bases of the bottles; the rest was fragments, many of them embedded in the wooden walls of the cupboard. We could only assume that the carbon dioxide had been slow to dissolve in the wine and the pressure had built up too fast. This could have been very nasty had he been holding a bottle at the time.
As they say in the extreme sports programmes, "Don't try this at home".