Cooking “purple sweet potatoes” or “purple yams”

Question

I recently bought something that was labelled at the grocery store as a "purple sweet potato". They were larger than what I am used to for sweet potatoes, but looked similar, although they had a purple skin on the outside and white flesh on the inside. I figured since they were labelled as "sweet potatoes", I would prepare them the same way I like to prepare regular sweet potatoes, by boiling them first (for about 40 minutes), then removing the skin, slicing it into wedges and then pan frying them. I have done this many times with normal sweet potatoes, and it works quite well.

However, after I boiled the purple sweet potatoes for 45 minutes, I pulled them out to take the skins off, and they were soft and stringy and incredibly off putting - they felt the same way as a gummy mashed potato would feel, and they fell apart all over the place.

Are they more like a potato, requiring less boiling time? Or is there something else going on here that I am missing?

Edit: I went to the grocery store today, and they are now labelled as "purple yams". I don't know if that makes a difference or not. I also got a picture of them, to make my description a bit clearer.

Asked by Ashley Nunn

Answer

I used to cook plenty of purple sweet potatoes when I was living in africa:) Sounds like you maybe cooked them too long...

They can be extremely tasty, sweet with a "perfumy" hint if you are lucky. They are best boiled with the skin on like you did and peeled afterwards (as the taste is preserved better that way). As for cooking time it really depends on the size (which means the potatoes are likely done at different times) but you can always feel when they are done by pressing on the potato with a fork - it should give slightly/be soft. I think it usually took me about 30min but I didn't use a clock. It may shorten the cooking time slightly to make holes in the potatoes with a fork (this also adds to the "creaminess").

I guess they do sometimes get a softer, more "creamy" consistency than your usual potato when well done. However the taste is richer and in my opinion far superior to orange sweet potato. If you prefer a firmer potato, just let your potatoes stay on the firm side (in my experience, though, the taste is enhanced by letting them go soft). But boiled ones would anyways mainly be for puddings as it gets rather sweet.

For panfrying I would suggest avoiding boiling the sweet pots first. Simply peel/wedge them raw, fry them as chips until done and serve with a spicy/hot dip - yum.

Answered by Heidi Larsen

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What determines sweet potato softness?

Question

I often make stews with sweet potato. I prepare it by cutting it about 1/2 to 1 inch every time, and stewing it for about 30-45 minutes.

I make sure to keep everything consistent but sometimes it ends up as hard as apple, and other times it turns to mush.

What makes the difference? The age of the sweet potato? The variety? Something else?

Answer

Edit: If cooking longer softens the potatoes, then this isn't what's happening. In that case, well, you just need to cook longer. The main variable is probably temperature (maybe the pot isn't actually all hot for all 30-45 minutes), followed by variations in cut size and in the firmness of the original potatoes. But the rest could apply to some readers too!

I'm going to take a wild stab at this. It can explain this sort of thing, but it does depend on how you cook your stew. The following is a quote from On Food and Cooking (excellent book!), one of my favorite discoveries from reading through the sections on fruit and vegetables.

It turns out that in certain vegetables and fruits - including potatoes, sweet potatoes, beets, carrots, beans, cauliflower, tomatoes, cherries, apples - the usual softening during cooking can be reduced by a low-temperature precooking step. If preheated to 130-140F/55-60C for 20-30 minutes, these foods develop a persistent firmness that survives prolonged final cooking. ... Firm-able vegetables and fruits have an enzyme in their cell walls that becomes activated at around 50C (and inactivated above 70C), and alters the cell-wall pectins so that they're more easily cross-linked by calcium ions. At the same time, calcium ions are being released as the cell contents leak through damaged membranes, and they cross-link the pectin so that it will be much more resistant to removal or breakdown at boiling temperatures.

So, if you started the stew from cold (or drastically reduced the temperature by dumping in the sweet potatoes and other things) and had it on low heat, so that it took a while to come up to temperature, then your sweet potatoes may have been in that 50-70C range where the enzyme is active for a while. So maybe while your length of cooking time is consistent, your time before simmering isn't; that could depend on how cold the ingredients were before adding, the pot you used, whether you got exactly the same setting on your stove, the temperature in your home, and so on. (I know you said this isn't it, but having larger chunks of sweet potatoes could conceivably contribute to that too; the inside would take longer to heat up, so you could end up with a firm interior, and the softer part on the outside could get rubbed off.)

Sweet potatoes do also vary some in firmness, but certainly not by that much. It could still be a factor, though, in combination with the rest! In any case, if you want to avoid the firm potatoes, I'd try making sure to get everything heated up quickly.

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Sweet potato storage?

Question

I've purchased a bunch of sweet potatoes but were unable to prepare them.

How long can i store a sweet potatoes before it spoils?

Also, what is the best methods or means of storing sweet potatoes. Are there any difference between storing regular potatoes and sweet potatoes?

Answer

Generally, the storage of sweet potatoes is similar to that of actual potatoes. Keep them in a cool, dark, dry place. Let them breathe (i.e. not in a plastic bag).

Your results may depend on the weather (temperature and humidity), but I live where it's hot and humid, and sweet potatoes will easily last two weeks. This is where potatoes may last only about a week or so.

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Preserving dehydrated fruits and vegs

Question

We bought a food dehydrator to make dog treats with. Primarily we're dehydrating yams, apples and bananas. I'm not dehydrating these to crisps because I didn't think I needed to. The dehydrated yams that we buy as dog treats are still pliable and leathery, so I didn't think I needed to dehydrate them totally dry.

The problem I'm having is that these treats are going moldy in about 4 days. Again, the treats we buy never go moldy. I'm assuming they're adding something to the commercial version to stop this.

Does anyone have some hints on what I'm doing wrong or any idea what the commercial brand is putting on them to stop this. The apples seem to be the slimiest first... Should I be drying the apples to crisps?

Answer

You get mold (and less visibly, bacteria) growth after 4-5 days because your water (humidity) content left in the deyhdrated food is greater than 5%. Typically dried apples (and other types of fiberous dried fruit) have humidity levels closer to 20% when you don't dry them to a crisp. That means the treats you make aren't shelf stable, but luckily this can be fixed with some experimentation.

Each food has it's own requirements for preservation. Here are some quick guidelines to try out on apples. For yams and bananas, I would try dehydrating them a bit more closer to being crisps.

Steps:

1. Wash fruits thoroughly before dehydrating. I don't do this, but you could try using a "fruit wash" (product for washing fruit).

2. Dehydrating isn't sterilization - the dehydrator isn't hot enough to sterilize the food, so some of these 'nasties' are left on there and waiting for their chance to grow. Commercial-grade food is always sterilized. Because a dehydrater isn't sealed well, I suggest you nuke the treats in your oven for 5-10 minutes on high heat AFTER you dehydrate the stuff, experimenting to make sure you don't dry them out too much in the oven. Also, be careful because the sugar is concentrated in dehydrated fruit, so it will burn easily. Wrapping the fruit in tin-foil before placing it in your oven is a potential trick because this effectively sterilizes the fruit in a steam bath. If you use foil, you'll need to cook them longer - start with 15 minutes.

3. After the treats are dehydrated and sterilized, try storing them in air-tight containers and always away from light in a cool/dark place. They need 7-10 days to "equilize" the moisture between each dried piece of fruit. Make sure to shake the containers every once in a while so they don't all stick together.

BEYOND THIS, there are more advanced techniques that you can easily try - including conditioning the dried fruits and a number of fruit-baths that preserve the fruits with harmless chemical solutions, like Ascorbic Acid (vitamin C). Try reading more on this link from UC Davis:

http://homeorchard.ucdavis.edu/8229.pdf

(Start Reading on Page 7).

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