This is already a standard feature of BeerSmith. You can add or subtract from your inventory in a number of ways.
Adding Inventory:
1) Create a shopping list from the recipes you want to brew. You can adjust the ingredient amounts to reflect the actual amount purchased. You then highlight the items and click Add to Inventory from the ribbon.
2) Go to any ingredient database, find the item, double click to open it and add the amount you have to your inventory.
3) Click the Inventory menu. Click to add any ingredient type. In the popup window, you can either scroll through or search for the name of the ingredient. At the bottom of the window, you can put in the amount and it'll add that to your inventory. If you already have some of the ingredient, what you add will add to that amount. You can also use a negative number to subtract from inventory, here.
Removing From Inventory:
1) You can adjust the actual amount in the ingredient inventory.
2) You can use the Inventory menu to remove part of your inventory.
3) In the recipe, The Remove from Inventory button is in the top ribbon. This will remove your whole recipe from the inventory. If you don't have enough in inventory, you'll get a popup and can choose to ignore the item. If you've already removed the items from inventory, you'll get a popup warning.
Now, once you have any item in inventory, as you create a new recipe you can click the "Show Only Items in Inventory" and see just that. Then, in any existing recipe, you can choose to see a column of how much if the ingredients you have on hand.
