Half an Onion, Half a Tin, and What to Do With the Rest

Everything here earned its place by changing an outcome. Nothing about using up part-used ingredients is included to round the number up.

The half you did not use

Half an onion, half a tin of tomatoes, a third of a pack of cream and four rashers of bacon is the standard residue of one meal. Individually each is trivial, and across a month they add up to a substantial fraction of what you spent on food. The failure is rarely intent and almost always visibility, since the half goes to the back of a shelf and is found a fortnight later.

The fix has two halves of its own: decide the second use when you open the item, and put it somewhere you will see it. Doing that consistently is worth more than any recipe for using up leftovers, because it prevents the problem rather than solving it.

Tins, jars and what happens after opening

Once a tin is opened the contents should be moved into a covered container, since the exposed metal can affect flavour and the tin is not designed for storage. Refrigerate the contents and use them within a small number of days, and check the label for a specific after-opening instruction.

Jars and cartons commonly carry an explicit use within period after opening, which is shorter than the unopened date and is the one that applies. Concentrated pastes, from tomato to curry, freeze well in tablespoon portions and are needed in that quantity anyway. Write the opening date on anything that has an after-opening window, because the printed date on the packet stopped being relevant when you opened it.

Freezing the awkward halves

Herbs chopped into an ice cube tray with oil or water become portioned flavour that keeps for months rather than days. Bread freezes sliced, and a slice goes straight from freezer to toaster with no thawing at all. Cheese freezes better grated than in a block, and the texture change matters much less in cooked dishes.

Wine, stock, cream and coconut milk all freeze in ice cube trays, which is exactly the quantity a single portion of sauce needs. Bag the cubes once frozen and label the bag, since a tray of unidentified frozen cubes is a small mystery nobody solves.

Vegetables that are past their best

Softening vegetables are usually fine for cooking even when they no longer look appealing raw, and the texture difference disappears in a soup. Roasting concentrates flavour and tolerates slightly tired produce better than any other method. Anything visibly mouldy, slimy or with an off smell should be discarded rather than trimmed, particularly soft produce where growth penetrates.

Stalks, tops and outer leaves often have more flavour than the part people keep, and they belong in a stock bag in the freezer. The distinction that matters is between past its best and actually spoiled, and it is a judgement made with your nose rather than a date.

A shelf that makes it visible

Designate one shelf or one box for opened and part-used items, and check it before every shop and before every meal. Clear containers matter more here than anywhere else in the kitchen, since the whole problem is that you forgot it existed.

In a small flat, keep it at eye level rather than at the bottom, because the bottom shelf of a fridge is where food goes to be forgotten. Once a week, cook one meal specifically out of that shelf, which is where the least glamorous and most useful cooking happens. This single habit removes more waste than any amount of careful shopping, because it deals with what has already been bought.

Buying to avoid the problem

Loose produce, deli counters and butchers let you buy the amount you need, and where available that is the cleanest solution. Where only packs exist, choose the format that survives, such as a jar of paste over a tin, or a resealable pouch over a rigid can. Frozen versions of high-waste items, particularly herbs, spinach and berries, are stored in exactly the quantity you take out.

Some ingredients simply do not work in single-person quantities, and choosing a different recipe is a legitimate answer. Track what you throw away for two weeks and you will find the waste concentrates in three or four items rather than being spread evenly.

Everything above, in order of what to do first

1. The half you did not use. Half an onion, half a tin of tomatoes, a third of a pack of cream and four rashers of bacon is the standard residue of one meal.
2. Tins, jars and what happens after opening. Once a tin is opened the contents should be moved into a covered container, since the exposed metal can affect flavour and the tin is not designed for storage.
3. Freezing the awkward halves. Herbs chopped into an ice cube tray with oil or water become portioned flavour that keeps for months rather than days.
4. Vegetables that are past their best. Softening vegetables are usually fine for cooking even when they no longer look appealing raw, and the texture difference disappears in a soup.
5. A shelf that makes it visible. Designate one shelf or one box for opened and part-used items, and check it before every shop and before every meal.
6. Buying to avoid the problem. Loose produce, deli counters and butchers let you buy the amount you need, and where available that is the cleanest solution.

The takeaway

Decide what the other half is for at the moment you open it, and put it where you will trip over it.

A home that works is a set of small systems, not one big clean.