1. What a potato is

The cultivated potato, Solanum tuberosum, was domesticated in the Andes thousands of years ago and later travelled around the world. FAO The part used in the kitchen is a tuber: a swollen underground stem that stores water and carbohydrate for the plant.

The tuber is the food. Leaves, stems, flowers and the small tomato-like berries produced above ground are not culinary ingredients: the vegetative parts and berries can contain high amounts of naturally toxic glycoalkaloids. Kew EFSA Glycoalkaloids occur throughout the plant; within the tuber, concentrations are generally greater around the peel, eyes and sprouts than in its centre. BfR

2. Varieties and cooking types

A variety, or cultivar, is the named potato — the name you may see on a seed catalogue, market sign or bag. In a British kitchen, the more useful question is usually whether that variety cooks waxy, floury or somewhere in between. Waxy potatoes stay moist, dense and intact; floury potatoes break into a drier, fluffier texture; an all-rounder sits between the two. British packs may skip the texture words and say what the potatoes are best for, such as salad, boiling, mashing, roasting, baking or chips. Treat that use label as the quickest buying guide. Potato texture varies by cultivar, while colour alone does not predict it. RHS

What you are making What to look for in a UK shop Why and what to watch
Boiled potatoes Waxy, salad or a boiling variety The flesh is less likely to split or shed into the water
Potato salad Waxy or salad potatoes They keep clean slices and survive dressing and mixing
Soups and stews Waxy for distinct chunks; all-rounder or floury when thickening is welcome Choose according to whether the potato should remain visible or melt into the broth
Gratin or dauphinoise Waxy to all-rounder The slices soften but keep the layered structure
Mash Floury, fluffy or a pack labelled for mashing Drain well and work gently so the mash does not turn gluey
Dumplings or gnocchi Floury A drier cooked potato usually needs less added flour
Jacket potatoes Floury or a baking variety Look for evenly sized tubers with a fluffy centre
Roast potatoes Floury, fluffy or a roasting variety The loose surface roughens well and forms a crisp crust
Chips A floury variety specifically sold for chips Dry matter and reducing sugars matter as well as texture, so a frying claim is more useful than skin colour

British growing and retail language adds another distinction: first early, second early and maincrop describe when a variety is ready to harvest, not how it must cook. Earlies are commonly sold and eaten as new potatoes; maincrops mature later, tend to produce larger tubers and include many varieties used for winter storage, roasting and baking. Sound, ungreen new potatoes usually need only a thorough scrub rather than peeling. Their moist, cohesive flesh is well suited to boiling and roasting, but is not the easiest route to exceptionally fluffy mash. Those labels do not replace the cooking description — an early can still be floury, and a maincrop can be waxy. RHS

Purple, blue, red and yellow flesh can add colour and distinct flavour, but it still does not tell you whether the potato will hold together. For a British recipe, match the bag’s stated use to the dish first, then use the named variety to repeat a result you liked.

3. Buying and choosing potatoes

Choose tubers that feel firm for their size. Dry soil on an unwashed potato is not spoilage; wetness trapped in a sealed bag is more concerning because it hides damage and favours decay. Look through the package for cuts, crushed areas, soft patches and excessive sprouting.

A few shallow marks can be trimmed before cooking. A large wet depression, spreading softness, visible mould, leakage or a sour or rotten smell is a reason to reject the potato. Avoid substantially green tubers and old specimens that are both strongly sprouted and shrivelled. BfR

Young potatoes often look smaller and may have papery skin that rubs away. That is normal, but it also makes them easier to bruise and less suitable for long storage. Mature potatoes should have a set, comparatively tough skin. UC Davis

“Organic”, “home-grown” and “unsprayed” describe how a crop was produced, not whether an individual tuber has been exposed to light, frozen, bruised or allowed to rot. Apply the same quality and safety checks.

4. Potato composition and behaviour during cooking

Raw potato flesh is mostly water. Most of its dry matter is carbohydrate, especially starch, with smaller amounts of fibre, protein, minerals and vitamins. Exact composition changes with cultivar, maturity, growing conditions, storage and preparation. Official food-composition records are therefore examples of a defined food form, not a promise for every potato. USDA FoodData Central

Potato starch contains two large glucose polymers, amylose and amylopectin. For the cook, their names matter less than what the starch granules and surrounding cells do. In the presence of water and heat, granules absorb water and gelatinise. At the same time, cell walls and the material holding neighbouring cells together soften. Cultivar, dry matter, starch properties and cell structure all influence whether cooked flesh stays waxy and cohesive or separates into a mealy texture. Texture review

This explains two apparent contradictions. A floury potato can collapse in soup yet make excellent mash. A waxy potato can give tidy salad slices yet produce dense, elastic mash. If any cooked potato is beaten aggressively, broken cells release more gelatinised starch; the mixture can become sticky or gluey. A ricer, masher or food mill used only until combined is gentler than a blender or food processor.

Evenly sized pieces reach the tender stage at roughly the same time. Rinsing cut potatoes removes loose surface starch; soaking can also remove some surface sugars. That can be useful for separate, crisp fries or shredded preparations, but it is not a ritual every potato dish needs. For soup, gratin or mash, washing away starch may work against the desired body.

5. Preparing potatoes before cooking

Wash potatoes under clean running water and scrub away soil. Do this even when peeling so the knife or peeler does not drag dirt across the flesh. Cut away small bruises and shallow damage until sound tissue remains.

Leave the skin on when it suits the dish and the potato is fresh, undamaged and not green. Young potatoes are the obvious candidates: their skin may need only a brush or a gentle scrape. BfR advises that only fresh, undamaged potatoes are suitable when the peel will be eaten. BfR

Cut pieces to an even thickness. A slicing disc is genuinely helpful for a large gratin, where uniform 3 mm slices matter; the published potato and zucchini gratin is a good example. A knife gives better control when trimming defects, quartering irregular potatoes or cutting a small batch.

Exposed flesh gradually browns. If potatoes must wait, submerge the cut pieces briefly in cold water, then drain and dry them. Do not leave them soaking for hours without a recipe reason: water can leach flavour and water-soluble nutrients, and a wet surface is the opposite of what roasting or frying needs.

6. Cooking methods and texture

Boiling. Start evenly sized pieces in cool water so the outside and centre heat more evenly. Keep the water at a controlled simmer, particularly for floury potatoes. Drain as soon as a knife enters without a hard core.

Steaming. Steaming limits direct water contact and is useful for potatoes destined for mash or dough. The pieces still need to be similar in size.

Roasting. Par-cooking is optional, but it lets you roughen a floury surface. In every case, evaporate or towel off surface moisture before adding fat. A dry surface heats beyond the boiling point of water sooner and browns more effectively. Aim for golden rather than very dark surfaces. FSA

Baking. Floury and all-purpose potatoes develop the clearest contrast between crisp skin and soft centre. Pierce only if your normal method or appliance instructions call for it; the important controls are an intact tuber, even cooking and a fully tender centre.

Frying. Dry cut potatoes thoroughly before they meet hot oil. Rinsing or soaking can help loose surface starch and sugar wash away, but drain and dry carefully. A sweet, cold-stored potato may brown before its centre is ready. The potato and zucchini fritters are a different fried preparation: finely grated potato and zucchini form the base of a batter held together by eggs and flour added gradually to suit the vegetables’ moisture.

Mashing. Use floury potatoes, drain them, return them briefly to the warm pan to drive off surface steam, then rice or mash. Add warm milk, cream or a little cooking water gradually. A food processor ruptures many cells quickly and is more likely to make gluey mash.

Gratin. Waxy or all-purpose slices give orderly layers; a flourier potato absorbs more moisture and softens the boundaries. Neither is automatically wrong. Slice consistently and give the centre enough time to become tender.

Soup. Choose firm cubes for a clear broth or an all-purpose/floury type when some breakdown should thicken the pot. In creamy Hokkaido pumpkin soup, potato supports the blended body rather than remaining as a visible cube.

Leftovers. Cool cooked potatoes promptly, refrigerate them within two hours and use within 48 hours or freeze, following the cited FSA household guidance. Reheat only the portion needed until steaming hot throughout. FSA leftovers guidance

7. Storage at home

For a short household stay, the priorities are simple: darkness, airflow, cool conditions and no trapped surface moisture. A paper sack, perforated bag, basket or ventilated box is better than airtight plastic. Light promotes greening; warmth accelerates sprouting and shrivelling; condensation and damaged tubers make rot easier to spread. Check the potatoes regularly and remove any that are deteriorating. Illinois Extension

A genuinely cool pantry or cellar is well suited to mature storage potatoes. A warm kitchen cupboard is only short-term storage. Young potatoes are more easily skinned and respire faster, so buy smaller quantities and use them sooner. UC Davis

At home, potatoes can be stored either in a cool, dark place or in the refrigerator. Cold storage can, however, increase sugars in some varieties, especially after longer storage. Those potatoes may taste sweeter and brown more quickly when baked or fried. Acrylamide can form when starchy foods are baked or fried at high temperatures; it is a substance whose dietary exposure should be reduced as a precaution. More sugar in a potato can encourage its formation, which is why cold storage is relevant here. A reviewed home-storage study found that refrigeration did not materially increase acrylamide-forming potential compared with a cool, dark place, so the UK FSA allows either option. FSA For fries and roast potatoes, watch for unexpected sweetness and rapid dark browning.

Raw potatoes do not freeze well by accident. Prepared potatoes can be frozen successfully when a method uses blanching or a fully cooked dish; freezing raw chunks without treatment commonly damages texture. Penn State Extension

Claims about never storing potatoes beside onions are repeated widely, but household evidence and explanations are inconsistent. The dependable rules are to give potatoes airflow, keep them dry to the touch, separate them from rotting produce and avoid trapping them with strong odours.

8. Cold damage, freezing and cold-induced sweetening

These are two different problems.

  1. A potato that actually froze: ice damages cells. After thawing, the flesh may look glassy or water-soaked, then become soft, wet and structurally broken. UC Davis describes tissue breakdown on thawing; Penn State notes that separated water can make a reheated potato watery. UC Davis Penn State A severely thawed, leaking or decaying potato belongs in the waste, not in dinner.
  2. A potato stored cold without freezing: some cultivars convert more stored carbohydrate into reducing sugars. The tuber can taste unexpectedly sweet, and those sugars brown readily during frying or roasting. This is cold-induced sweetening. It can affect flavour, colour and acrylamide formation at high heat, but it is not the same as frozen tissue. FSA

For a sweet-tasting but otherwise sound potato, a boiled or steamed use avoids chasing a pale fried colour. Some cold-sweetened potatoes lose part of the sweetness after time at a moderate room temperature, but cultivar and storage history matter, so this is not a guaranteed “reset”.

Neither phenomenon has anything to do with sweet potatoes, which are a different plant.

9. Green potatoes, sprouts, bitterness and glycoalkaloids

Green colour is chlorophyll produced after light exposure. Chlorophyll itself is not the toxin, but greening is a visible sign that the tuber has been stressed by light, conditions that can also raise glycoalkaloids. The intensity of green is not a home measurement of glycoalkaloid concentration. EFSA

Potato glycoalkaloids, chiefly alpha-solanine and alpha-chaconine, are concentrated particularly around the peel, eyes and sprouts. Damage and sprouting can also be associated with higher amounts. At sufficient concentration they can cause acute illness; unusual bitterness or a burning sensation in the mouth is a warning to stop eating the dish. BfR

Official consumer wording is not perfectly identical across countries. BfR advises generously removing green areas and eyes, while also saying that old, dried, green or strongly sprouting potatoes are unsuitable. A sensible household interpretation is conservative:

  • a firm potato with one small, shallow green patch or tiny emerging eye may be peeled and trimmed generously if the remainder is completely sound;
  • discard a potato that is substantially green, strongly sprouted, shrivelled, damaged across a wide area or bitter;
  • if a cooked dish tastes markedly bitter, do not keep eating it;
  • do not rely on cooking to rescue a heavily affected potato.

Peeling, boiling and frying can reduce glycoalkaloid content to varying degrees, but EFSA reports broad ranges rather than a universal household guarantee. The compounds are not reliably eliminated by ordinary cooking. EFSA

Not every mark is rot, and not every internal cavity is a plant disease that a cook can diagnose.

Finding Usually means Kitchen decision
Superficial scab Corky surface lesions formed while growing Mainly cosmetic; peel or trim if desired. Extension guidance considers scabby potatoes edible, though they may store less well. UAF
Bruise / black spot Mechanical impact; colour may develop below the skin Cut through it. Use the potato if the remaining flesh is firm, normal-smelling and extensive decay is absent.
Hollow heart A cavity in the centre associated with growth conditions Trim the discoloured cavity; an otherwise sound potato is edible. University of Idaho
Grey or black internal discolouration May follow bruising, oxygen limitation, storage or a physiological disorder A small dry area can be removed; reject widespread, wet, foul or uncertain damage. UC Davis
Soft rot Wet, collapsing tissue, often with leakage and odour Discard the whole potato and check its neighbours.
Mould Visible fungal growth, sometimes with soft or damp tissue Discard rather than cutting a token spot from a compromised tuber.

A dry corky defect is not equivalent to a wet, spreading lesion. Conversely, an attractive skin does not overrule a rotten odour or collapsing flesh. Do not try to diagnose late blight, bacterial soft rot or another crop disease from a description alone; the kitchen question is whether the tuber remains sound food.

11. Nutrition and health context

Potatoes are principally a water-rich starchy food. A USDA record for boiled potato flesh cooked in the skin without salt reports carbohydrate as the main energy-providing nutrient, very little fat, and useful amounts of fibre, potassium and vitamin C. Values vary with portion, cultivar, whether skin is included, storage and cooking. USDA FoodData Central

Preparation changes the nutritional context more than a simple “potatoes are healthy/unhealthy” label can express. A plain boiled potato and a deep-fried, heavily salted potato product are not nutritionally interchangeable. Oil adds energy and fat; cream, cheese and butter change both energy and saturated fat; salt changes sodium. Those ingredients can be part of a meal, but they belong in the description rather than being attributed to the tuber itself.

When cooked potatoes cool, some of their starch rearranges into a form the body does not digest as readily. It is called type 3 resistant starch. Cooked and chilled potatoes usually contain more of it than potatoes served just cooked, but the amount depends on cultivar and method. Resistant-starch review

Glycaemic response is also context-dependent. Variety, cooking, mashing, cooling, reheating, portion size and the rest of the meal can all influence the response. Research on chilled and reheated starches does not give one result for every potato meal; the SPUD review specifically describes mixed findings between foods and preparation patterns. SPUD Project A single glycaemic-index number should not become a moral ranking of a food or personalised medical advice.

12. Potatoes versus sweet potatoes

A similar appearance does not mean close botanical relatedness. Potato is Solanum tuberosum in the nightshade family, Solanaceae. Sweet potato is Ipomoea batatas in the morning-glory family, Convolvulaceae. Kew explicitly describes them as not closely related. Kew potato Kew sweet potato

Sweet potatoes are true storage roots, not potato stem tubers. Their sugars, starches, moisture and cell structure also behave differently, so a sweet potato is not an automatic one-for-one substitute in mash, gratin, fries or dough. A dedicated guide can treat those differences properly.

13. Potato products and uses beyond the kitchen

Potato starch is the purified starch separated from crushed tubers. In the kitchen it thickens sauces, contributes crisp coatings and changes the texture of noodles and baked products. Potato flakes are cooked, dried potato designed to rehydrate; instant mash therefore is not simply raw starch in a box.

Crisps and fries are products whose texture depends on cultivar, slice geometry, moisture removal, sugar level, oil and heat. Their nutrition reflects the whole process, including added oil and salt, not only the starting potato.

Outside food, native and modified potato starches have long been used for adhesion and thickening — for example in paper manufacture, adhesives and textile processing. Specialised starch derivatives also appear in other industrial formulations. These uses depend on processing and specification; a kitchen bag of potato starch is not a substitute for a pharmaceutical or materials-grade ingredient. Industrial review

14. Potatoes in world cuisines

There are many ways to cook a potato: grate it raw, boil it, brown it or blend it. In Slovak bryndzové halušky, raw grated potato forms the base of a soft dumpling dough. Italian potato gnocchi use cooked potato and flour, while Swiss rösti and many Central European potato pancakes start with grated potato browned in a pan. In Spanish tortilla española, egg holds the potato slices together. French gratin and pommes Anna rely on thin layers; vichyssoise is instead a smooth potato-and-leek soup.

Potatoes also appear in South Asian aloo dishes, Irish colcannon, Polish pierogi fillings and many kinds of bread. In some dishes they stay in firm pieces; in others they become mash, dough or a creamy soup.

15. FAQ

Do young potatoes need peeling?

No, not when they are fresh, well scrubbed, undamaged and not green. Their thin skin is often pleasant. Peel for a smoother texture or to remove damage. BfR limits skin-on advice to fresh, undamaged potatoes. BfR

Can I eat sprouted potatoes?

A firm potato with a tiny new eye can be peeled and the eye removed generously. Strong sprouting, shrivelling, widespread damage, green colour or bitterness shifts the decision toward discarding. There is no universal sprout-length test. BfR

What should I do with a green patch?

For one small shallow patch on an otherwise firm potato, official guidance allows generous removal. Discard substantially green potatoes and any potato that tastes bitter. Greenness signals light exposure but cannot quantify glycoalkaloids. EFSA BfR

Should potatoes be stored in the refrigerator?

A cool, dark, ventilated place remains a good default. Current UK FSA guidance also permits the refrigerator for household waste reduction because its reviewed study found no material increase in acrylamide-forming potential versus cool, dark storage. Frying quality and sweetness can still vary by potato and storage history. FSA

Why did my potatoes taste sweet after storage?

They may have undergone cold-induced sweetening: sugars accumulated during cold storage. This is not the same as freezing. Sweetened potatoes can brown quickly when fried or roasted.

Why do potatoes turn dark after cutting or cooking?

Cut flesh can brown when damaged cells meet oxygen. Brief cold-water holding slows it; dry the pieces before high-heat cooking. Grey colour that appears after cooking is a different, cultivar- and storage-dependent phenomenon. A dry colour change is not automatically rot, but wetness, softness, mould or foul odour calls for disposal. ÚKZÚZ UC Davis

Why do potatoes fall apart when boiled?

The potato may be floury, the pieces may be uneven, or the boil may be too vigorous or long. Choose waxy potatoes for clean-edged pieces and simmer gently. Texture review

Can I freeze raw or cooked potatoes?

Accidentally frozen raw potatoes often thaw watery and soft. For deliberate freezing, use a tested method: blanch prepared pieces or freeze a suitable cooked dish. Texture varies, so trial a small batch. Penn State Extension