title_body: How to make 50 litres of cold coffee from ground coffee?
upvoted_answer: I use almond milk bags and a one gallon pitcher. 
  I grind French Roast coffee beans for 36 cups on a semi-course grind, fill the milk bag with the grounds, add cold water to the pitcher with the bag inside, let it sit on the counter over night. The next morning my cold brew is ready to add ice and water for drinking (I make mine half water, half cold brew, as it is strong). I store mine in a 64 ounce growler in the refrigerator. Multiply that by the quantity you need. I have included links, only for pictures. If I were to purchase, I would look for the best deal.
  https://www.amazon.com/Pro-Quality-Nut-Milk-Bag/dp/B00KLT6X9W
  https://www.amazon.com/Rubbermaid-711717429960-Gallon-Covered-Pitcher/dp/B00YF7II9O/ref=sr_1_10?s=home-garden&amp;ie=UTF8&amp;qid=1548194608&amp;sr=1-10&amp;keywords=1+gallon+pitcher+with+lid
  https://www.amazon.com/Growler-64-Ounce-Phenolic-Kombucha-Distilled/dp/B075ZZNNJZ/ref=sr_1_73?s=home-garden&amp;ie=UTF8&amp;qid=1548194678&amp;sr=1-73&amp;keywords=growlers+for+beer