Do potatoes turn into sugar in the fridge? The science of 'cold-induced sweetening'

November 6, 2025 •

4 min read

According to the UK's Food Standards Agency, storing potatoes in the fridge can actually be harmful. This is because the cold temperatures cause the potatoes' starch to convert into sugar, a phenomenon known as cold-induced sweetening (CIS). The changes in sugar content affect taste, texture, and can lead to the formation of potentially harmful compounds during cooking.

Quick Summary

The refrigeration of potatoes causes their natural starch to convert into simple sugars like glucose and fructose, a process called cold-induced sweetening. This conversion is a survival mechanism for the potato tuber, but it negatively impacts the potato's taste and texture. Crucially, higher sugar levels can also lead to increased formation of the chemical acrylamide when cooked at high temperatures. Proper storage in a cool, dark place is key to preventing this issue.

Key Points

Cold-Induced Sweetening: Low temperatures in a fridge trigger enzymes in potatoes to convert stored starch into simple sugars like glucose and fructose.
Taste and Texture Impact: This conversion results in a sweeter flavor and a gritty or waxy texture, undesirable for most savory dishes.
Increased Acrylamide Risk: High sugar levels in refrigerated potatoes can lead to significantly higher levels of acrylamide, a potential carcinogen, when cooked at high temperatures.
Optimal Storage Conditions: The best place to store raw potatoes is a cool (6–10°C), dark, and well-ventilated location, such as a pantry or cellar.
Reconditioning Process: To reverse the sugar accumulation in refrigerated potatoes, they can be warmed to room temperature for a few weeks before cooking.
Ventilation is Key: Storing potatoes in an open container or paper bag improves air circulation and prevents moisture buildup and spoilage.
Avoid Light: Exposure to light causes greening and the production of solanine, a natural toxin.
Keep Away From Ethylene Gas: Never store potatoes near onions, apples, or bananas, as the ethylene gas they release accelerates sprouting.

The science behind the conversion of starch into sugar in potatoes stored at cold temperatures has significant implications for home cooks and food processors alike. A potato's physiological response to cold, or cold-induced sweetening (CIS), is a fascinating process that directly impacts its culinary properties and even its nutritional safety. The core of this issue lies in the potato's survival mechanisms and the subsequent chemical reactions that occur when it is later cooked.

The Biochemistry of Cold-Induced Sweetening

At its most basic level, a potato is a storage organ for starch, a complex carbohydrate. This starch is a food reserve for the plant. When exposed to cold temperatures, typically below 10°C (50°F), the potato's natural enzymes, such as invertase, become active. These enzymes catalyze the breakdown of the starch molecules into simpler sugars, specifically glucose and fructose. This biological adaptation helps protect the plant's cells from freezing by acting as a natural antifreeze. However, for a potato destined for human consumption, this process creates several culinary and health-related issues.

Impact on Taste, Texture, and Appearance

The shift from complex carbohydrates to simple sugars changes a potato's characteristics in several ways:

Sweeter Flavor: The most direct and noticeable effect is a distinctly sweeter taste. This can be undesirable for savory dishes and alters the intended flavor profile.
Gritty Texture: As the starch structure breaks down, the potato can develop a gritty, waxy, or crystalline texture, especially when cooked. This compromises the expected fluffiness of a baked potato or the crispness of a roasted one.
Darker Appearance when Cooked: This is a major concern, particularly for processed potato products like chips and fries. During high-temperature cooking, the newly formed reducing sugars (glucose and fructose) react with amino acids in the potato through a process called the Maillard reaction. This causes accelerated and uneven browning, leading to dark, unappetizing results.

The Link to Acrylamide Formation

Beyond cosmetic and taste issues, the conversion of starch to sugar in the fridge is linked to the formation of a potentially hazardous compound. When high-sugar potatoes are baked, fried, or roasted at high temperatures (above 120°C or 248°F), the Maillard reaction produces not only browning but also the chemical acrylamide. Acrylamide is a substance known to have carcinogenic properties in animal studies and is classified as a 'probable human carcinogen' by international health agencies. By storing potatoes correctly and minimizing this sugar conversion, cooks can significantly reduce the risk of acrylamide formation in their prepared dishes.

How to Prevent Cold-Induced Sweetening

To avoid this problem, proper potato storage is essential. The key is to keep them in an environment that is cool, but not cold enough to trigger the CIS response.

Ideal Storage Conditions: The optimal temperature for storing raw potatoes is between 45–50°F (6–10°C). This range effectively slows down sprouting and metabolic processes without causing sugar accumulation. Good storage locations include cool cellars, basements, or pantries.
Proper Ventilation: Potatoes should be stored in a well-ventilated container, such as a paper bag, wire basket, or jute sack. This allows moisture to escape and prevents the build-up of fungus and bacteria. Avoid sealed containers like plastic bags.
Avoid Light: Keep potatoes in the dark to prevent them from turning green, which produces the mildly toxic compound solanine.
Keep Away from Ethylene: Store potatoes away from ripening fruits like apples, bananas, and onions. The ethylene gas they release can cause potatoes to sprout and spoil faster.

A Comparison of Storage Methods


Storage Method	Ideal Temperature	Nutritional Changes	Acrylamide Risk	Culinary Impact
Refrigerator	Below 10°C (50°F)	Starch converted to sugar. Vitamin C content may be preserved initially.	High (especially with frying/roasting) due to increased sugar content.	Sweet, gritty taste and texture; darker fried color.
Cool, Dark Pantry/Cellar	6–10°C (43–50°F)	Minimal starch conversion, minimal vitamin loss for several months.	Low, as sugar levels are stable and low.	Maintained original flavor and texture.
Room Temperature	Above 10°C (50°F)	Faster sprouting and metabolic activity; some vitamin C loss over time.	Low, as long as tubers are used quickly.	Best for short-term storage (1–2 weeks).
After Reconditioning	Move from cold to warmer temp	Free sugars reconverted to starch or respired away over several weeks.	Lowered risk, as sugar levels are reduced.	Restores better flavor and color to cold-stored potatoes.

The Final Verdict on Storing Potatoes in the Fridge

Ultimately, understanding the physiological changes that occur during cold storage is key to making informed decisions in the kitchen. While a refrigerator might seem like the natural choice for preserving food, it is detrimental to the quality of a raw potato. The sweet flavor, compromised texture, and increased risk of acrylamide are all compelling reasons to store potatoes correctly. By opting for a cool, dark, and well-ventilated pantry or cellar, you can maintain the potato's intended taste and texture, ensuring both delicious and safer culinary results. For potatoes that have already been in the fridge, a process called reconditioning—warming them to room temperature for a few weeks—can help reverse some of the sugar conversion before cooking. This strategy offers a way to salvage refrigerated potatoes, though storing them correctly from the start is the best practice for optimal nutrition and flavor.

Conclusion

In conclusion, the claim that potatoes turn into sugar in the fridge is scientifically accurate and has significant implications for food preparation and safety. This conversion, known as cold-induced sweetening, is a natural response to low temperatures and dramatically alters the potato's culinary properties. The result is a sweeter, grittier potato that produces more acrylamide when cooked at high heat. Proper storage in a cool, dark, and well-ventilated space, rather than the refrigerator, is the best way to maintain potato quality and reduce potential health risks. For those who have already refrigerated their potatoes, reconditioning is an option to mitigate the effects, though starting with correct storage is always the best path for optimal nutritional benefits.

Frequently Asked Questions

Raw potatoes get sweet and gritty in the fridge because the cold temperatures, typically below 10°C, activate enzymes that convert the potatoes' starches into simple sugars like glucose and fructose, a process called cold-induced sweetening.

While potatoes stored in the fridge are generally not immediately harmful to eat, cooking them at high temperatures (like frying or roasting) can create higher levels of acrylamide, a potentially carcinogenic compound. The taste and texture will also be altered.

To prevent potatoes from turning into sugar, store them in a cool, dark, and well-ventilated place, such as a cellar, basement, or pantry, where temperatures are ideally between 6°C and 10°C (43-50°F). Avoid storing them in the refrigerator.

Acrylamide is a chemical compound formed during high-temperature cooking (frying, roasting) when the reducing sugars from potatoes (glucose and fructose) react with the amino acid asparagine. Since refrigerated potatoes have higher sugar levels, they produce more acrylamide when cooked, which is a probable human carcinogen.

Yes, you can mitigate the effects of cold-induced sweetening through a process called reconditioning. By moving the potatoes to a warmer room temperature (around 15°C or 60°F) for a few weeks, some of the sugar can be converted back to starch or respired away.

Yes, once cooked, potatoes should be stored in the refrigerator to prevent the growth of bacteria. The cooling and cooking process prevents the cold-induced sweetening effect and the subsequent formation of acrylamide.

For long-term storage, keep potatoes in a cool (6-10°C), dark, and well-ventilated place like a pantry or cellar. Use a breathable container like a paper bag or a basket, and ensure they are kept away from ripening fruits that emit ethylene gas.