Civil war soldiers on both sides had a very simple diet.[12] Food could not be preserved with refrigeration or by canning, as both were later inventions.[12] Soldiers ate hardtack (hard biscuits made with flour, water and salt), salted pork, bacon and occasionally beef preserved with potassium nitrate .[12] However, hardtack was the most common food. It was cheap, easy to store and ship to the troops.[12] However it could and did break soldier's teeth and often contained worms.[12] During the trench warfare at the Siege of Petersburg, officers continually had to tell soldiers to keep the trenches clean and not throw their hardtack in the trenches.[12] A soldier famously replied: “We’ve thrown it out two or three times, sir, but it crawls back”.[12]