To write off stock, use Stock Adjustment Qty- to remove the goods from stock. This reduces the quantity on hand, the value of the quantity on hand, and expenses it to the 5-XXXX Stock Adjustments account.
Writing off stock in bulk is achieved via a stocktake session and the resulting stock adjustment.
Once you have identified all the stock to be written off, you can add the stock to a stock non report group which then allows you create a stocktake session for just that stock group.
Add Count in the stocktake session, and make it all 0 Qty>, then Confirm Count. Jim2 will create the stock adjustment for you on a status of Booked. Finish that stock adjustment to write it off the stock.