The study, published in BMJ Nutrition, Prevention & Health, was authored by scientists at the Holy Spirit University of Kaslik in Lebanon. In the paper they admitted they didn't know why apple cider vinegar might have a slimming effect. Apple cider vinegar comes in two forms, ones containing the 'mother' and ones that have been filtered. The 'mother' is a culture of good bacteria that is added to apple cider vinegar as part of the fermentation process. It can give apple cider vinegar a cloudy appearance or take the form of gelatinous looking layer at the top of the liquid.