We recently had a client ask us to check the condition of their cider before they bottled it. The cider was to contain enough sugar at bottling so a secondary fermentation in the bottle would occur and a sparkling cider would result.
The cider maker wanted any yeast in the cider to ferment the available sugar, get a certain amount of carbon dioxide produced and have the cider on the market within weeks. So we were asked to do a full microbiological analysis and also to check the sulfur dioxide levels.
Our testing revealed that there was no free sulfur dioxide present, plenty of acetic acid and lactic acid bacteria and a small level of Saccharomyces yeast. The producer was then concerned that the levels of bacteria could produce off-flavours in the bottled cider, with no sulfur dioxide present to inhibit the bacteria.
The producer appeared to have decided to use less sulfur dioxide in this batch of cider than in their previous productions. However, these results showed that this was not the best course of action for the style of cider they were making. The agreed treatment was to add a higher level of sulfur dioxide in these products in future to remove the bacteria present and then to re-test the cider prior to bottling, to ensure it is suitable for bottling.