The Science Behind The Separation
The simple act of keeping onions and potatoes on opposite sides of your kitchen isn’t just good organization – it’s rooted in plant biology that most home cooks never learn about. While onions don’t produce significant ethylene gas themselves, they can still affect nearby potatoes through moisture and other factors and spoil more quickly. What makes this particularly fascinating is that potatoes are incredibly sensitive to this invisible gas, almost like having an overly dramatic friend who reacts to every small thing.
Both vegetables emit gases that can affect the condition of each other – onions can accelerate the spoilage of potatoes, while potatoes can cause onions to sprout more quickly. Think of it like two roommates with incompatible lifestyles – one’s late-night activities keep the other awake, and nobody wins. At the same time, potatoes give off moisture as they sit, which can cause nearby onions to become moldy or mushy.
Why Ethylene Gas Acts Like Nature’s Spoiler
According to storage experts, the primary issue isn’t ethylene gas from onions, but rather moisture and storage condition incompatibility. When stored near potatoes, this gas encourages them to sprout and soften more quickly. The irony here is almost comedic – while ethylene can actually be used professionally to prevent sprouting in controlled environments, in your pantry, it becomes the villain of freshness.
In the case of potatoes, ethylene exposure can trigger the sprouting process. As potatoes age, they naturally produce ethylene, which encourages the formation of sprouts from the eyes (bud-like structures) on the surface of the tubers. Potatoes are sensitive to ethylene, and even small amounts of this gas can accelerate the sprouting process. Storing potatoes near ethylene-producing fruits or vegetables can lead to premature sprouting, reducing their quality and shelf life. It’s like having a house guest who accidentally triggers everyone else’s allergies just by breathing.
The Moisture Problem Nobody Talks About
Beyond the gas exchange drama, there’s another moisture-related issue happening behind the scenes. Onions contain a lot of water. All you need to do is slice an onion and cook it covered on low heat (called ‘sweating’) to discover just how much water. Meanwhile, potatoes are cured, or dried, before being brought to market. Keeping them dry helps preserve them.
This fundamental difference in moisture content creates a storage nightmare when they’re housed together. The onions are basically humidity machines, constantly releasing moisture into the air, while potatoes are trying their best to stay dry and dormant. Furthermore, the moisture content of potatoes can negatively affect onions. Potatoes have a relatively high moisture content, and if stored in close proximity to onions, this moisture can encourage the onions to sprout or become moldy.
Optimal Storage Temperatures That Actually Matter
Here’s where things get really specific, and where most people realize their kitchen pantry isn’t exactly a controlled environment. Experts recommend potatoes be stored at a temperature between 45 and 50 degrees Fahrenheit, and that onions be stored in a cool, dry place. Find a storage solution that maintains a cool but not cold temperature between 45-50°F (7-10°C). Avoid storing potatoes in the refrigerator, as it can alter their taste and texture.
The refrigerator, which many people assume is the safe choice, is actually terrible for both vegetables. While potatoes and onions prefer cooler temperatures, storing them in the refrigerator is not recommended. Potatoes can become too cold and become sweet, while onions may become soft or moldy due to excess humidity. Potatoes also store better in high humidity – as high as 90 percent. Not surprisingly, a root cellar would be the perfect place for potatoes. Most of us don’t have root cellars, but understanding these numbers helps explain why both vegetables go bad so quickly in modern homes.
Humidity Requirements That Seem Impossible
The humidity requirements for proper storage sound like something from a scientific laboratory rather than practical home advice. Long term storage tests at 0–10°C indicated that for potatoes the optimum relative humidity was 98–100%, whereas for onions a lower humidity was required. For potatoes, the high relative humidity minimized moisture loss, generally reduced decay and maintained firmness and a thin skin.
Keep onions in a well-ventilated area at 56-76% humidity (ideal) and between 45-55 degrees. Meanwhile, Potatoes prefer medium humidity, around 80-90%. Look for a storage option that can maintain an appropriate level of moisture to prevent drying out or sprouting. Onions need a lot less humidity – ideally, 65-70 percent – but just as much ventilation as potatoes. These requirements are so different that it’s almost like trying to make a desert plant and a rainforest plant happy in the same terrarium.
The Light Factor Most People Ignore
It’s also a good idea to keep potatoes in the dark. Overexposure to light can cause a buildup of solanine, an alkaloid that potatoes naturally produce to repel insects. Light also causes an increase in chlorophyll, which gives a green hue. So, potatoes that have a green tinge also likely have higher levels of solanine, which is toxic at high levels.
Darkness matters: Potatoes should be stored in a dark place to avoid light exposure, as sunlight can cause them to develop a green tint and produce solanine, a toxic compound. Bulbs must be kept in darkness. Whenever a light is switched on inside the storage facility, the onions in the light (on top of a pile) will react as if they were in direct sunlight, and start to sprout. Both vegetables are basically vampires who hate artificial lighting, but for completely different biological reasons.
Professional Storage Methods We Can Learn From
Large-scale storage facilities have figured out solutions that home cooks can adapt. During the warm summer months in North America, refrigeration is necessary to keep temperatures low, so potatoes are stored in controlled atmosphere conditions. The closed rooms must have good ventilation to prevent the build-up of ethylene gas, carbon dioxide, and respiration heat, while maintaining the right relative humidity to prevent weight loss and sprouting.
The Multiserver programme for drying onions will ensure that the turbines work the maximum number of hours to extract moisture from the onions as quickly as possible, whilst maintaining the temperature between 25 and 30°C, and the relative humidity between 60% and 65%. In doing so, the aim is not to dehydrate the insides of the bulbs, but rather the 3 or 4 outer layers which separate the bulb from the outside. These industrial methods show just how precise the science needs to be for optimal storage.
Container Choices That Actually Work
Use a storage container that’s well-ventilated, such as a crate, a cardboard box with holes punched in it, or any container that will allow any excess moisture to evaporate. When it comes to containers, onions should breathe, so keeping them in a mesh bag, basket, or crate is advisable. Avoid sealing them in plastic bags, as this can trap moisture and lead to spoilage.
In fact, the National Onion Association says not to store onions in plastic bags, because the lack of air movement will cause them to go bad more quickly. Ventilation is key: Choose a storage solution that allows airflow to prevent moisture buildup, which can lead to rotting. The common theme here is airflow – both vegetables need to breathe, even though they can’t be roommates.
When Storage Goes Wrong: Warning Signs
If some of your potatoes have turned green, it’s likely from sunlight exposure and you should not eat them. If your potatoes have gone soft, wrinkled or have sprouted more than a few centimeters, they’ve likely gone bad. Signs of spoilage include a soft or mushy texture, mold growth, unusual discoloration or odor, or sprouting. If you notice any of these signs, it’s best to discard the affected potatoes or onions.
Any onions that get a soft spot or look like they are going to sprout should be used immediately. Like potatoes, regularly check stored onions for any signs of rot or sprouting, and remove any affected onions promptly to protect the others. One bad apple really does spoil the bunch, and the same principle applies to both onions and potatoes – contamination spreads quickly in confined spaces.
