На оф. сайте Куперса:
"The code on the yeast sachet is a Julian Date, representing the date that the yeast was packaged rather than a “Use By” or “Best Before” date. e.g. a sachet with 25007 was packaged on the 7th of September, which is the 250th day of 2007. While the beer kit, containing this yeast sachet, may have been produced on Thursday the 13th of September 2007, carrying a Best Before date of 13/09/09."
И про "просроченный" экстракт есть:
"Coopers Beer Kits contain hopped liquid malt extract. Liquid malt extract darkens over time and develops toffee/molasses like aromas and flavours. This process is accelerated when temperature is increased. This is not such a bad thing with intentionally dark brews but may be undesirable with lighter styles. If you wish to persist with making up a brew past its Best Before date (out of curiosity or otherwise) it’s worth getting fresh yeast from a Brewing Specialist store to ensure that the brew ferments thoroughly."