Sweet potatoes are a healthy and nutritious alternative to standard white potatoes. They’re great for those on a Low GI (low glycaemic index) diet and are versatile and high in fibre, minerals and vitamins.
But, like all fresh fruit and vegetables, they do have a shelf life and will go bad if stored improperly.
This article will cover everything you need to know about sweet potatoes going bad.
How to Tell if a Sweet Potato is Bad
As sweet potatoes age, they develop several key signs that indicate they’re beginning to turn bad. All of these signs are noticeable without cutting into the tuber or having to taste the sweet potato.
Older sweet potatoes will develop small brown spots, about the size of the tip of your little finger. Once these spots appear, it’s a sure indicator that this sweet potato should be eaten as soon as possible.
The exterior (skin) colour of the sweet potato will begin to change; this can vary across different sweet potato varieties. The more common orange-fleshed sweet potato skin will turn from its grey-brown colour into a darker brown or even black.
However, the purple-skinned sweet potato will turn from shades of red to dark purple as it ages. Inside that purple skin, the white flesh will become yellowish and slowly absorb the purple from the outer skin.
Will start to appear, usually from the ‘eyes’ of the potato. If left to grow, these sprouts will develop into roots, and if planted in the soil will eventually produce leaves and more sweet potatoes.
These can be found on the surface of the skin, and inside the flesh when cut. They’re usually caused during growing, by fluctuations of moisture and temperature, and aren’t something to worry about – they’re perfectly safe, but the tuber will be less dense and lack flavour.
Mould or Rot
This sign is impossible to ignore. It can appear as either a grey/white bloom or as a grey-green fur; this can be peeled away from the flesh of the sweet potato before cooking, as it will not affect the flesh.
But, if there are any black rot spots, this is a key sign of a fungus that has infected the sweet potato, and it should be discarded immediately – it is unwise to ingest this rot, as it can cause stomach upsets, and will taste unpleasant.
An ageing or rotting sweet potato has a distinct aroma; first it will smell sweet, the sour, and ultimately the smell will become akin to pungent compost.
This smell is due to the fibres and sugars within the sweet potato breaking down; this can also cause small tears in the skin and a thick syrup-like substance to leak out.
This can only be judged by cutting into the sweet potato tuber. A fresh sweet potato will have a dense texture, no discernable fibres, and be bright orange or white in appearance.
A sweet potato that is going, or has gone, bad will be soft and mushy, or stringy, and have patchy colours with white fibres visible in the centre of the tuber.
Sweet potato tubers that look and feel like this are no longer edible and should be discarded immediately.
How Long Do Sweet Potatoes Last
Sweet potato tubers that are best bought fresh, preferably as close to their growing location as possible. When kept in ideal conditions, sweet potato tubers can last for quite some time. However, these times do vary a lot according to where and how the sweet potato is being kept.
Sweet potatoes have a high percentage of water in them, and this is what will speed up their ageing process. A rough guide to these time limits can be judged by whether the sweet potato is raw or cooked, kept at room temperature, in the fridge, or even in the freezer.
For raw, unprepared, fresh sweet potatoes; a general rule of thumb is to keep them for up to 5 weeks in your pantry. But, if kept in the fridge, you can keep them for as long as 3 months without incident.
Cooked, or prepared sweet potatoes will not last more than a few hours if left at room temperature. They are best kept in the fridge or freezer. You can store cooked sweet potatoes for up to 7 days in the fridge, in an airtight container.
Or, they can be kept in an airtight container in the freezer for as long as 6 months.
Sweet potatoes will also keep for a long time if canned or bottled. This is a simple process to extend the life of your sweet potatoes and can be done at home without any fancy equipment.
On the pantry shelf, a can or jar of prepared sweet potatoes can keep for up to 1 year, so they’re a great pantry staple for year-round eating. However, an opened jar or can of prepared sweet potatoes will only keep for 1 week and should be kept in the fridge once opened.
Prepared sweet potatoes, as fries, chips, or mash, will keep for 4-6 months in the freezer. But, once thawed in the fridge, they will only keep for 2-3 days, so it’s important to enjoy them before then!
How to Store Sweet Potatoes
Not storing your sweet potatoes properly will also increase the swiftness of their deterioration.
It’s also important, when choosing your sweet potatoes, to carefully select tubers in excellent condition, and only purchase sweet potatoes that are free from any blemishes (spots, holes, sprouts, or soft spots) or other signs of ageing, as these will keep the longest.
When it comes to storing your sweet potato tubers you do have several great options. But, there are a few places you definitely should not keep your tubers! Places to avoid keeping your sweet potatoes include:
On the Kitchen Counter or Worktop
Keeping your sweet potatoes here is a bad idea. The ambient light and warmer temperatures will hasten the ageing of the tubers, and you can expect to see sprouts and discolouration within a week.
In damp/moist areas: anywhere that has moisture in the air, or dampness will also increase the rate of ageing. Moisture easily gets into the tuber through the papery skin and increases the degradation of the flesh.
You can expect to see signs of rotting and mould within a couple of weeks, and you should be able to smell the mould/rot too.
The best places for you to keep your sweet potato tubers are in a pantry, the fridge, or in your freezer. In each case there are certain criteria you’ll need to stick to, to ensure the maximum shelf life is achieved.
For instance, if you do want to freeze your sweet potatoes you’ll need to par-boil or blanch them first.
This is because the tubers already have high water content, and freezing them raw will cause this water to crystallise. These crystals then break up the fibres, and when the sweet potatoes are thawed they become mushy.
To successfully freeze your sweet potatoes you can boil/steam/microwave them for a few minutes, or just until the outer third flesh begins to soften. Allow the sweet potatoes to cool, and then package them into airtight containers or ziplock bags before freezing.
Keeping your potatoes in the fridge is a great option if you have space. Moisture and light are the worst enemies for these tubers, so if possible, keep them in the vegetable crisper in a dark and open container. This will help to prevent light from reaching them, but also allow for air to move around the tubers to prevent moisture build-up.
This is by far the easiest and most common place to store sweet potato tubers. To keep them successfully for the maximum shelf life all you need to do is follow these easy steps: keep them dark, dry, and cool.
Dark: As mentioned, light is bad, it encourages the tubers to start sprouting. So keep your tubers in a dark bag, preferably fabric and not plastic. You can also keep your sweet potatoes in a box with a lid, this will keep them nicely and prevent accidental damage from knocks etc.
Dry: Moisture is a prime cause of spoilage for all vegetables, especially sweet potatoes. To prevent this, keep them in a way that air can easily move around them; fabric bags, open boxes or containers can also help stop moisture build-up.
Cool: Just a touch cooler than room temperature is great, ideally around 40-50˚F/5-10˚C. Generally, in a basement or cellar is the perfect location, or anywhere that is cool in a kitchen – under the sink is usually cool, but watch out for moisture!
To Sum Up
Fresh sweet potatoes should appear regularly in our diets, as they are an incredible vegetable; packed with minerals, vitamins and fibre.
You can tell if they are going bad due to brown spots, changing color, sprouts and holes appearing, weird smells, mould growth and soft or mushy texture.
Keep them in a dark, dry, and cool place for maximum shelf life.