How do you achieve quantative tightening?
When a U.S. Treasury bond matures the principle is repaid in money. If the owner of the bond is the Federal Reserve, it can reinvest the money in an asset like a U.S. Treasury bond. If the Federal Reserve wants to reduce the money supply the receipt of the money is coincident with a reduction in the account of the federal government. Since it is computerized they do not have to destroy any currency and coins; they change a number in a computer.