Dry Yeast for Beer Brewing

How much dry yeast do I need and do I have to rehydrate it?

Fermentis recommends 50 to 80 g of dry yeast per 100 litres of wort, which is about 11.5 to 18 g for a 23 litre batch, so a single 11.5 g sachet suits a standard batch of normal-strength beer. Higher-gravity beers need a higher rate. Dry yeast can be pitched directly by sprinkling it gradually over the wort surface at or above fermentation temperature so it does not clump. Or rehydrate it first by sprinkling it into at least 10 times its weight of sterile water or boiled, cooled wort at 25 to 29°C, leaving it for 15 to 30 minutes, stirring gently and then pitching the slurry. Dosage and temperature ranges differ between strains and brands, so check the instructions on the sachet you choose.