Food Source Information Potatoes

The potato (Solanum tuberosum L) is a starchy, tuberous vegetable in the nightshade family, Solanaceae. A tuber is any enlarged root or stem that stores nutrients for the plant and from which shoots will grow. Potatoes were introduced outside the Andes region four centuries ago and have become one of the world’s most economically important and widely consumed vegetable.

Potato flesh is a complex carbohydrate and the most affordable source of potassium in the produce department. Each year more than 1 million acres of potatoes are planted and 41.3 billion pounds are harvested. China has become the largest producer of potatoes worldwide. There are hundreds of types of potatoes sold in the United States, which fit into seven categories: russet, yellow, red, blue/purple, white, fingerling, and petite. Each has its own unique taste, texture, and appearance, making the preferred cooking methods different for each variety.

Reds: These potatoes have a smooth, moist texture that is good for soups and stews because, even when cut, they maintain their shape throughout cooking. ‘New’ potatoes are produced in the spring or early summer and have a waxy texture and a thin skin.

Russets: These are generally larger in size and make up most of the U.S. crop. They are commonly used for baking, mashing, and making gnocchi.

Yellows: This varietal has a golden flesh and creamy texture. Yukon Golds are famous for their yellow color and rich, starchy flavor.

Specialties: These include fingerlings and blue/purple potatoes, such as Purple Majesty and Mountain Rose. Their unusual color lends dishes an unusual appeal. Ideally used mashed, roasted, or in salads.

In the 1840s a major plant disease outbreak caused by potato blight, an organism which can infect vegetables in the nightshade family, swept across Europe, killing most of the potato crops. This led to the Irish Potato Famine and the disappearance of Europe’s primary food source; almost one million people died from starvation and disease. The first permanent U.S. potato crops were established in Londonderry, New Hampshire in 1719. From there, they spread widely to the rest of the states. Today, Idaho, Washington, Wisconsin, North Dakota, and Colorado are the top potato producing states.

Over 100 potato varieties are grown in Colorado, with most production located in the San Luis Valley. At 7,600 feet, this is one of the highest altitude potato production areas in the world. In Colorado, potato harvest begins in September with about 98% of the crop going to storage before being shipped.

Food safety issues associated with potatoes often involve prepared dishes, such as potato and other deli-style salads and baked potatoes. Potatoes have been the culprit in a multitude of foodborne-illness outbreaks and are ranked by the Center for Science in the Public Interest (CSPI) as one of the 10 riskiest foods consumed in America. Between 2000 and 2020, at least 292 potato-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 9,197 illnesses, 251 hospitalizations, and 8 deaths. Food safety issues associated with potatoes often involve baked potatoes and prepared dishes, such as potato salads or other deli-style salads.

In 1994, an outbreak of botulism was attributed to potatoes. A Greek restaurant in El Paso, Texas used baked potatoes that were wrapped in foil and held at room temperature for several days to make traditional Greek dips called skordalia and melitzanosalata. Thirty persons were sickened after consuming the dips; 21 of them were hospitalized, including four who required mechanical ventilation.

Between June 5 and 7, approximately 5,600 people were infected by a strain of E. coli O6:H16 in Orland Park, Illinois. Iwan’s Deli and Catering in the Chicago suburbs prepared food for over 530 events with over 25,000 people in attendance. While multiple food items were served at these events, potato salad was identified as the likely vehicle of transmission. Just prior to the outbreak, the deli had received a below-average health inspection score and was cited for 15 health code violations, including failure to wear gloves while preparing ready-to-eat foods and kitchen sinks lacking soap and towels. Iwan’s closed its doors to business six months after the outbreak.

A 1999 outbreak of Norwalk-like Viral Gastroenteritis sickened nearly 200 people in Anchorage, Alaska after a company luncheon. After notifying the Alaska Division of Public Health, a questionnaire was sent out to employees found that among the 236 attendees who ate potato salad, 183 (78%) became ill. Further investigation found that the potato salad was prepared by two days before the luncheon by an ill food handler who had used bare hands to mix the ingredients.

Potato salad was also the likely source of a Salmonella gastroenteritis outbreak at a reception in Connecticut in 2009. Investigation into this outbreak identified two serotypes among infected individuals, Salmonella enterica Schwarzengrund and Typhimurium. Environmental investigation by the local health and public health departments observed food service workers at the restaurant having bare-handed contact with ready-to-eat foods and did not have adequate handwashing practices, however the contamination mechanism leading to the outbreak is unclear.

Baked potatoes were implicated in a 2012 botulism outbreak among inmates at the Utah State Prison when a baked potato saved from a meal served weeks earlier was added to prison-made illicit alcohol known as prune (Thurston et al. 2012). Eight inmates were hospitalized after consuming the prune, with three requiring mechanical ventilation.

A large botulism outbreak occurred in April 2015 as the result of improperly prepared potato salad served at a church potluck in Fairfield County, Ohio. Twenty-nine people fell ill, and one died of respiratory failure during the incident. An investigation by the CDC and the Fairfield County health department revealed that the associated food was home-canned potatoes used to make potato salad. The potatoes had been processed using a boiling water canner rather than a pressure canner. It is important to use a pressure canner when home canning because this method kills C. botulinum spores, while boiling water canners do not.

In 2016, potato salad prepared by Big G food stores was implicated in an outbreak of Salmonella Braenderup in Marengo, Iowa. The Iowa Department of Public Health (IDPH) investigated 23 cases, all of whom had consumed Big G potato salad. The IDPH collected potato salad samples from the grocery store’s deli, where the potato salad had been prepared, and found six samples containing the outbreak strain of Salmonella. Of the 23 cases, three were hospitalized; no deaths were reported.

The potato is normally grown from “seed potatoes”, which are small tubers or pieces of tuber sown to a depth of five to ten cm. The planting density of a row of potatoes depends on the size of the tubers chosen, while the inter-row spacing must allow for ridging of the crop. Ridging (or “earthing up”) consists of mounding the soil from between the rows around the main stem of the potato plant. Ridging keeps the plants upright and the soil loose, prevents insect pests such as the tuber moth from reaching the tubers, and helps prevent the growth of weeds.

The use of chemical fertilizer depends on the level of available soil nutrients; in irrigated, commercial production, fertilizer requirements are relatively high. However, potatoes can benefit from the application of organic manure at the start of a new rotation. It provides a good nutrient balance and helps maintain the structure of the soil. The soil moisture content must be maintained at a relatively high level. For best yields, a 120 to 150-day crop requires from 20 to 27.5 inches of water. Crop rotation using pest-tolerant varieties and healthy, certified seed tubers are strategies used in avoiding crop losses. Insect pests can wreak havoc on a potato crop. However, damage caused by the Colorado potato beetle, a major pest, can be reduced by destroying beetles, eggs, and larvae that appear early in the season. In addition, sanitation, crop rotations, and use of resistant potato varieties help prevent the spread of nematodes.

Production Issues

Yellowing of the potato plant’s leaves and easy separation of the tubers from their stolons indicate that the crop has reached maturity. If the potatoes are to be stored rather than consumed immediately, they are left in the soil to allow their skins to thicken. Thick skins prevent storage diseases and shrinkage due to water loss. However, leaving tubers in the ground for too long increases their exposure to the fungal incrustation called black scurf.

Potato Storage and Handling

Because newly harvested tubers are living tissue and subject to deterioration, proper storage is essential. Proper storage both prevents post-harvest losses of potatoes marketed for immediate consumption or processing and guarantees an adequate supply of seed tubers for the next growing season. For potatoes that will be processed, storage conditions are aimed at preventing “greening” (the buildup of chlorophyll beneath the peel, which is associated with the formation of solanine, a toxic alkaloid) and losses in weight and quality. The tubers should be kept in a dark, well-ventilated environment with high relative humidity (85 to 90 percent) and at a temperature of 43–46.5°F.

Potatoes should not be washed by consumers before storing, as dampness promotes early spoilage. For home storage, potatoes should be stored in a well-ventilated cool, dry, and dark place, ideally between 45–55°F. Potatoes should not be stored at refrigerator temperatures because this can cause potato starches to convert to sugars, resulting in a sweeter taste and excessive darkening during cooking.

Potatoes and other vegetables in the nightshade family can produce solanine, an alkaloid compound that causes potatoes to turn green and have a bitter flavor. Solanine production by a plant is a chemical defense mechanism against insects, disease, and predators. Potato leaves and stems contain this compound and therefore should never be consumed. Solanine, in small doses is toxic and can lead to headaches, nausea, vomiting, diarrhea, and paralysis of the central nervous system; in large doses it can be fatal. Potatoes can develop solanine if they have been exposed to light (especially florescent light) or extreme cold or warm temperatures for prolonged periods of time. If green discoloration is noticed on a potato, the green can be cut off and discarded.

When some potatoes are cut but uncooked, they may take on a pinkish or brownish discoloration. This process is called enzymatic browning, which occurs when the flesh of the potato is exposed to oxygen. Potatoes that become discolored are safe to eat and do not need to be discarded. The color usually disappears with cooking. Storing in cold water or adding lemon juice or vinegar to the water can prevent discoloration. Soaking in water should be limited to two hours to retain water-soluble vitamins which are leaked during soaking.

Sprouts are a sign that the potato is trying to grow. Storing potatoes in a cool, dry, dark location that is well ventilated will reduce sprouting. Sprouts should be cut away before cooking.

Prepared potatoes are considered a Time/Temperature Control for Safety (TCS) food and must be properly cooled. Cooked potatoes are moist, contain protein, and have a neutral or slightly acidic pH, which makes them predisposed to bacteria growth. In addition, both the surface of raw potatoes and the soil they are grown in can contain botulism spores—which are usually not killed by baking—and foil-wrapping potatoes creates an anaerobic environment conducive for the spores to germinate.

More than a billion people worldwide eat potatoes, making potatoes of the most important food crops. In 2020, nearly 84% of US households purchased potatoes and total dollar sales increased by 16.4%, totaling over $13 billion. The tuber is commonly baked, boiled, fried, and used in a multiple of dishes, including mashed potatoes, potato soup, potato salad, potato pancakes, twice-baked potatoes, and potatoes au gratin. Frozen potatoes are a main processed potato product, including frozen French fries that are served in fast-food chains and restaurants. Potato chips are also popular processed snack food, produced from thinly sliced fried potato.

As with all fresh produce, hands should be washed before preparing potatoes. Potatoes should be washed well under running water and scrubbed with a clean vegetable brush before cooking or baking. Peeling can remove the hard-to-clean outer surface. Prepared dishes should be stored properly to maintain a safe temperature, outside of the temperature danger zone. The following are recommendations for specific potato dishes:

Potato salad: it is best to cool down the cooked potatoes to 40°F BEFORE mixing in other ingredients. The prepared potato salad should be kept at refrigerated temperatures, 40°F or less, until ready to serve.

Baked potatoes: if heating baked potatoes in foil to serve later, ensure that the potato cools quickly and is stored in the refrigerator until used. A thermometer should be used to verify potatoes are reheated to 140°F before serving.

Mashed potatoes should be prepared with pasteurized milk and kept at a proper temperature: above 140°F during serving or at 40°F or less for storage.

For more information on how to keep potatoes stored properly and fresh please visit FoodKeeper App

Potatoes are sometimes accused of being fattening; however, by itself, one serving of white potato contains very little fat (generally listed as zero grams of total fat per serving) and contains only 26 grams of total carbohydrate. Frying potatoes in oil or adding butter and sour cream can more than double the calories in a potato product.

Potatoes are high in both soluble and insoluble fiber (from three to seven grams depending on their size). It is beneficial to cook and eat potatoes with the skin on as that is where half of the potato’s fiber, much of its potassium, and many other important nutrients are found. The potato skin contains Vitamins B and C, calcium, and it is rich in phytochemicals, which may help to protect the body from chronic diseases. Potatoes contain significant amounts of iron, providing women with 25% and men with 57% of their recommended daily value; 88% of the total amount of iron in a baked potato is found in its skin. A common misconception, however, is that all of a potato’s nutrients are located in its skin; approximately half of the dietary fiber found in a potato is found within the potato itself.

As with many other vegetables, the method of cooking can affect the bioavailability of certain nutrients. Nutrient losses are greatest when boiling, as water-soluble vitamins and minerals will leach out into the cooking water. To maintain the highest nutrition of a cooked potato, steaming or microwaving are the best choices.

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