After boiling, the hopped wort is now cooled, ready for the <answer>yeast</answer>. In some breweries, the hopped wort may pass through a hopback, which is a small vat filled with hops, to add aromatic hop flavouring and to act as a filter; but usually the hopped wort is simply cooled for the fermenter, where the <answer>yeast</answer> is added. During fermentation, the wort becomes beer in a process which requires a week to months depending on the type of <answer>yeast</answer> and strength of the beer. In addition to producing ethanol, fine particulate matter suspended in the wort settles during fermentation. Once fermentation is complete, the <answer>yeast</answer> also settles, leaving the beer clear.
What substance settles and make beer clear after it ferments? 
yeast