Saturday, September 13, 2014

Fruit "Ice Cream" with ≤ 2 ingredients

A few weeks back, Katie found a recipe for two-ingredient peanut butter-banana ice cream, with which we are currently infatuated (although there's no sign of this being 'just a phase').  This recipe is itself an adaption of the one-ingredient banana ice cream, which apparently has been known among strict herbivores for many years. (Can you guess what the one ingredient is?)  While both of these recipes would more appropriately be labeled 'sorbet' (although they don't quite fit that label, either), they produce a frozen dessert that really does have the consistency and mouthfeel of ice cream.  So, what is it about bananas that makes them so special?  And more importantly, can we do something similar with the last of the incoming apples and plums from the yard, now that our jam coffers are full for the year?

The general recipe calls for cutting bananas of the appropriate ripeness into small pieces, freezing them, then mashing them (e.g., in a food processor or blender).  When the mash warms up a little, the 'grains' coalesce, producing the 'ice cream.'  How does it work?  The 'one-ingredient' recipe linked above mentions that bananas work well because they are high in pectin.  But many other fruits are also high in pectin--would it work just as easily with them?  This article explains that it's a little more nuanced than that--it's not just pectin, but pectin, fiber, and sugar that work together to give the creamy texture. (From a physical chemistry perspective, the smaller the ice crystals in the product, the creamier it will feel.  The sugar and polysaccharides decrease water's ability to form and grow ice crystals by messing with water's hydrogen-bonding network.)

So, fruits that are high in pectin, fiber, and simple sugars should be able to make a nice creamy sorbet/ice cream (sorbeam?), too.  Time to compare some data!

Fruits with a lot of sugars, fiber, and pectin give a creamier texture in one-ingredient 'sorbeams.'  Data sources are here, here, and the paper linked here.  A qualitative list of pectin levels in fruit can be found here (and many other places online).  Bananas are unique in their high content of available sugars, nearly twice as high as the other kinds of fruit for which we could find numbers.  So, in theory, it should work a lot better with bananas than almost any other fruit.  But hey, we're experimentalists!  Why don't we try it with our apples and plums anyway, and see if we like it!  (After all, if if it's not all that good, Jake will eat it anyway.)

At first, the frozen fruit (apples, here) makes sort of isolated granules.

As it starts to warm up, the granules start to stick together, but it stays kind of icy.  It's vaguely reminiscent frozen applesauce--not bad, but not what we're shooting for.

But add bananas, and bam!  Creamy ice-cream-like texture.

Same thing for the plum as for the apple. (If you leave the peels on, they stay in the sorbeam as fun confetti sprinkles!)

You can scoop it into bowls and top it with dried apple slices and cinnamon, or whatever normal people put on ice cream.

The sorbeams made from either just apples or just plums were good, but not quite as creamy as we've grown accustomed to with the bananas.  So we wondered, what if we mixed these with banana sorbeam to improve the texture?  And it worked!  The table shows Katie's response to each experiment.  Moreover, since the banana is a fairly subtle flavor, especially if the bananas aren't overly ripe, the mixtures really tastes more like apple or plum with just a hint of banana. Also, mixing in some sugar with the solo apple sorbeam made it taste less like frozen applesauce and a little more creamy, consistent with our hypothesis that it's the relatively low sugar content preventing the just-apple sorbet from being awesome. (We didn't try adding sugar to the plum.)

The amount of banana flavor depends on the ripeness of the bananas. (The creaminess of the texture, to some extent, too.)  While visiting family in July, we were introduced to a new term for bananas with brown spots: giraffey (adj.: having the appearance of giraffe).  We've expanded the concept to develop an entire animal-themed scale of banana ripeness.  Further to the right gives more banana-ey flavor; too far to the left makes the sorbeam taste starchy and astringent.  We like somewhere between giraffe and black bear; those less fond of banana flavor could edge toward puffer fish, but definitely don't go all the way to hummingbird.  Photo credits for hummingbird, puffer fish, giraffe, black bear: Wikipedia.  Other sources for the green, yellow, spotty, and black bananas.

How do you prepare frozen fruit desserts?  Let us know in the comments section below!

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