Tag Archives: The Art of Fermentation

Sweet Potato Fly Recipe

A Soft Drink from Guyana

Sweet Potato Fly is a soft drink recipe that originally comes from Guyana, a small country on the northern coast of South America. I read about it in The Art of Fermentation by Sandor Ellix Katz. It is the kind of drink sold in the street markets at stalls, bottled in large plastic bottles and dispensed to customers. It is a good example of a local-made substitute for soda that is shipped in from elsewhere.

Elevating the Sweet Potato

The drink itself, elevates the sweet potato to another level. The fermentation process seems to bring out some of the subtle flavors in a raw sweet potato that get lost in the translation of cooking it. According to Sandor Ellix Katz, the best seasonings to accompany the sweet potato in this drink are the so-called “Christmas spices” – cinnamon, nutmeg and ginger.

Sweet PotatoWhen the fermentation has gone a few days in it’s primary fermentation vessel it is moved into a sealed container where carbonation can develop. The carbonation makes it a soft drink and therefore an alternative to store bought soda. The carbonation also seems to bring out more flavor as well as it imparts a sharp note of acidity that can counterbalance the sweetness. Much in the same way that salt can bring out the flavor in foods, even sweet ones. Carbonation can do the same thing for beverages.

The Recipe

In the Art of Fermentation book it calls for 2 large sweet potatoes per gallon. When I think of large sweet potatoes, I think of those monster ones. So for a half gallon use one monster one or two medium ( think of the size of a regular Russet potato ) sweet potatoes.

Makes one half gallon
  • 1 very large or 2 medium sized sweet potatoes, cut into small pieces, shredding them works well. This might be a good job for a food processor if you have one.
  • 1 cup of sugar. You have choices here, brown sugar imparts more flavor and is what I generally go with, white if you want to keep it mild. Don’t use honey as the antimicrobial agents present naturally in honey will retard fermentation.
  • A cinnamon stick, or the equivalent amount of powdered cinnamon. The benefit of the stick is that it stays in one piece and is not a bunch of small particles floating around, in other words, better aesthetics in the final product.
  • Other spices to your liking. Ginger works well either powdered or in it’s raw form. Nutmeg and allspice work well also. Start out with a teaspoon or so of each and then adjust up to taste.
  • A  starter culture. 1-2 ounces. A live culture to start the fermentation. I use water kefir, which I have plenty of if anyone needs some, just reach out to me. Other things that would be worth trying that have a similar biological spectrum of microbes would be whey, which can be obtained from yogurt. It’s the liquid that forms on top of yogurt when it sits around for a while. Yogurt itself, or dairy kefir would be a good choice, but it will make the product cloudy as it introduces milk solids.

The Process

Take the sliced/grated sweet potatoes and put them in a vessel that will hold them, give them several rinsing of water to remove the surface starches that have developed from the cutting process. I stir them and then let them sit and soak for 30 minutes and stir occasionally. Then I repeat this again for a second rinse.

Once the sweet potatoes are rinsed, add sugar, spices, starter culture and add a few ounces less than a half gallon of water, 58-59 ounces would be perfect. Stir well and cover lightly. I used a stainless steel cooking pot, the pot lid keeps it covered but will not allow pressure to build. Always use a vessel that is non-reactive to acids as the fermentation process will acidify the liquid and you don’t want anything to leach into the liquid.

Let the mixture sit for 2-3 days at room temperature. If it is in an opaque container it is fine to sit out on a counter top. If it is clear or translucent, it is best to keep it covered or in a dark place. UV light from the sun and even florescent lighting can interact with the biochemistry that is occurring in the container and cause “off flavors” to develop.

Foam will develop on top which indicates that fermentation is occurring. It is OK to stir it occasionally and taste it to check the progress by using a clean utensil. The flavor of it will also shift with time and it is interesting to see how this develops.

Ready to Bottle
Ready to Bottle

After 2-3 days it should have some small foam bubbles on top and will be ready to bottle. Strain the liquid out of the container and put that into a seal-able container, leaving an inch or two of air space at the top. Just like soda bottles have from the store. I highly recommend plastic, a recycled soda or at least a juice container is a good idea. This drink can carbonate so vigorously that I would not trust a glass container to bottle it in.

Bottle Conditioning

Once bottled in the sealed bottle, let it sit at room temperature for 1-2 days until it gets hard from the pressure that has built up in it. It now can be drank and stored in the refrigerator, which will greatly slow the fermentation down. The one nice thing about a drink like sweet potato fly is that it will ferment slowly in the refrigerator, so it will re carbonate itself after the bottle is opened. This pretty much happens overnight, if you use some one day the next morning it will have built up enough pressure to re-carbonate, at least this is what I have observed.

Bottled Sweet Potato Fly - Half Gallon
Bottled Sweet Potato Fly – Half Gallon

What to do – Leftover Sweet Potato Pieces

Almost 1 Quart of Leftover Sweet Potato Pieces
Almost 1 Quart of Leftover Sweet Potato Pieces

I have used the leftover pieces of sweet potatoes in pancakes. I use a high ratio of sweet potatoes to batter. Basically the batter is just a binder to hold the pieces of sweet potato together.

The sweet potatoes are softer than in their raw state as they have been predigested by the fermentation process. On top of this they have absorbed some of the flavor of the spices from the liquid that they have been sitting in for several days. If you like, you can even fortify the batter with the same spices that were used in the sweet potato fly recipe and make the flavor stand out even more. I have even made them a bit savory with salt, cumin and coriander, giving it a curried type of flavor profile.