Three staples that are not really ingredients yet
A sack of onions, a head of garlic and a bag of potatoes are the closest thing most kitchens have to a permanent stock, and they are also the items most often found sprouting, soft or unusable at the bottom of a cupboard. The waste is routine enough that people treat it as unavoidable.
It isn’t, quite. All three are storage organs — a swollen stem in the case of the potato, layered leaf bases in the onion, a cluster of them in garlic — and each was built by the plant to sit through an unfavourable season with its reserves intact and then to grow when conditions improve. Every storage failure is the organ doing exactly what it’s designed to do, on the plant’s schedule rather than the cook’s.
Dormancy ends when the conditions say it should
After harvest these organs enter a dormant period during which they will not sprout regardless of how they are kept, and that period varies by variety from a few weeks to several months. Once it passes, the tissue becomes responsive, and warmth and moisture are the two signals it responds to.
That is why the same bag can sit quietly for six weeks and then sprout in three days without anything visibly changing. Nothing changed outside; the internal clock ran out. It also explains why some varieties are sold as keepers and others are not, and why a bargain sack late in the season may have very little dormancy left in it.
Sprouting draws on the reserves stored in the organ, which is why a sprouted onion goes soft in the middle and a sprouted potato goes light and slightly sweet. The food is being spent on the new growth. Removing the shoot does not put anything back.
Humidity and light do most of the remaining damage
Onions and garlic want dry air and reasonable circulation, because moisture on the skins supports the moulds that turn a bulb soft and black at the neck. Anything that traps humidity around them — a sealed plastic bag, a closed drawer, a bowl on a counter next to a kettle — shortens their life dramatically.
Air movement is the part most often overlooked. A bulb sitting in a solid container is surrounded by a still layer of its own moisture, whereas the same bulb in an open basket or a net dries its own surface continuously. That is the entire reasoning behind the braid, the net bag and the wire basket, all of which look like tradition and are in fact ventilation.
Potatoes want the opposite, which is the crux of the problem. They lose water readily through their skins and go wrinkled in dry air, so they keep best somewhere cool, dark and slightly humid. Light is the other enemy, since exposed potatoes turn green as chlorophyll develops, and the greening is accompanied by an increase in bitter compounds that are worth cutting away generously.
They should not be stored together
The common practice of keeping onions and potatoes in the same basket works against both. Potatoes give off moisture, which is precisely what onions do not want, and both give off gases that hasten the other towards sprouting. It is one of the few kitchen rules that is genuinely worth following rather than merely traditional.
Garlic is the most tolerant of the three and the most sensitive to cold. A whole head kept dry and airy will last for months, while one in the refrigerator sprouts quickly, because the chill acts as the signal that the unfavourable season has passed. Peeled cloves are a different matter entirely, having lost their protective skin, and they need to be treated as a fresh ingredient.
Reading a bulb before you buy it
Weight is the most useful test available. An onion that feels light for its size has been losing water, and a potato that gives under the thumb has spent its reserves. The neck of an onion should be dry and tight; softness there is the beginning of rot and it spreads inward invisibly.
Buying in smaller quantities more often is the unglamorous answer to most of this, and it is the one that suits a kitchen without a cool dark room attached to it. A sack bought cheaply and stored badly is not a saving once a third of it has gone. Whether that trade is worth making depends entirely on what your storage actually looks like rather than on what the arithmetic says at the shop.
For potatoes, the practical distinction is between a firm dry skin and one that rubs away at a touch, which indicates a very young tuber that has not cured and will not keep. And a green tinge anywhere is a reason to leave it. None of these are exotic tests, and all of them are more informative than the size and the price, which are the two things a shopper usually looks at first.
Common questions
Should potatoes go in the refrigerator?
Ordinary domestic refrigeration is colder than a potato wants, and it converts some of the starch to sugar, which changes the flavour and makes the potato brown much faster and darker when fried. A cool dark cupboard is generally better. The advice has shifted over the years and remains somewhat contested, so it is worth judging by how you plan to cook them.
Is a sprouted onion safe to use?
The onion itself is usually fine as long as it is firm and smells right, and the green shoot inside is edible too. What has changed is the texture and the sweetness, since the bulb has spent some of its reserves. A soft, damp or foul-smelling neck is a different matter and means the bulb should go.
Why does garlic sometimes turn blue or green?
Sulphur compounds in garlic can react with trace metals and with acid to form coloured compounds, particularly in young garlic and in pickles. It looks alarming and is a harmless colour change rather than spoilage. Older garlic and less acidic conditions make it far less likely.
Senior writer, Wah Taste
Mateo joined to cover everyday cooking, street food, spice & pantry and stayed for the awkward questions and thinks most subjects are more interesting once you know how they work.
