49

I'll try to make this as brief as possible:

Dissolved two teaspoons of table sugar (sucrose) in about 250ml water. Sipped it, and as expected it tasted sweet. I let the rest of it sit in the freezer overnight. Next day, I took out the frozen sugar solution and, well, licked it.

Surprisingly, I could barely taste any sugar in it. It was almost as though I was licking regular ice.

Why is it that I'm not able to perceive any sweetness here?

I was under the impression that since the solution, being a homogeneous mixture of sugar and water, was sweet, the "popsicle" I made ought to taste sweet too (since the sugar would be evenly distributed over the volume of the ice).

paracetamol
  • 18,649
  • 29
  • 106
  • 169
  • 3
    Maybe reduced vibration cause slower diffusion through the mucosa and/or lesser rate of collision with receptors?However, nice observation. Popsicles taste sweeter when they melts; at least to me. –  Apr 24 '17 at 14:55

1 Answers1

68

Where is the sugar?

When you freeze a dilute aqueous sugar solution pure water freezes first, leaving a more concentrated solution until you reach a high concentration of sugar called the eutectic concentration. Now you have the pure water that's frozen out, called proeutectic water, and the concentrated eutectic sugar solution from which the sugar is finally ready to freeze along with the water. Upon freezing this eutectic composition forms a two-phase eutectic mixture, in which the sugar may appear as veins or lamellae (like veins of some ores among Earth's rocks, though these typically form form a different process). If that structure is in the interior of the ice cube, likely since you cooled the solution from the outside, then licking the outside you got only the pure water proeutectic component.

See https://en.wikipedia.org/wiki/Eutectic_system for more about this process.

Addendum: I tried this with store-bought fruit juice which was red in color. Poured it into an ice tray and froze it overnight in my household freezer. It appeared to be a homogeneous red mass and tasted sweet, but was also mushy implying some liquid was still present (after overnight freezing for an ice cube sized sample). The juice was roughly 10% sugar by weight.

Oscar Lanzi
  • 56,895
  • 4
  • 89
  • 175
  • 19
    Another possible reason could be that taste-buds get kinda deactivated at low temperatures. – Pritt says Reinstate Monica Apr 23 '17 at 12:26
  • 9
    @PrittBalagopal they do get numb with frozen foods, but the amount of heat loss needed to balance the temperature drop from licking an ice cube is not enough to cause such effect. It is the same as frozen ice cream. You sense the taste once the bite melts. – Mindwin Remember Monica Apr 23 '17 at 12:48
  • 11
    Yes, that's why you need to stir and churn continuously if you want to make sorbet. – bobflux Apr 23 '17 at 13:15
  • 4
    So sugar water is a non-eutectic mixture? Interesting. And this non-eutectic mixture cools down until enough pure water freezes, transforming the rest (sugar+ yet unmelted water) into a eutectic mixture. I'm just trying to wrap my head around this. – CowperKettle Apr 23 '17 at 15:40
  • 1
    @CopperKettle that's basically how it works. A binary mixture is eutectic (where it can be so) only at the right concentration of both components. At any other composition the component in excess freezes out to get the composition to eutectic, then it's freezing party time for everybody. – Oscar Lanzi Apr 23 '17 at 23:55
  • 11
    So, in summary: "The sugar is on the inside of the ice. You're licking the outside, which is nearly all water." ? – Malady Apr 24 '17 at 03:25
  • 3
    @Mindwin But icecream is still needs a lot more sugar to get the sweet taste than a room-temperature treat. It's not quite as bad as what the OP is observing, but it's a very real effect anyway. – Luaan Apr 24 '17 at 09:28
  • @Luaan that is because nobody just gives one single lick to ice cream. – Mindwin Remember Monica Apr 24 '17 at 11:59
  • 5
    Can you color the sugar (or use something else) to be able to see these veins in the ice? – Aaron McMillin Apr 24 '17 at 16:55
  • Water doesn't freeze from the outside: it freezes from up to bottom because ice floats. If the answer were right, liking the bottom of the ice cube should taste sweet - even sweeter than water tasted. Anyway, because of my child experience of using a freezer to make popsicles, I'm afraid @Luaan is right and what the OP experiences is just that frozen food tastes less sweet, even if it's homogeneous. – Pere Apr 24 '17 at 22:55
  • @Pere I would expect that in a glass of water, the ice would start to form on the edges (surface) of the glass, which would kind of make it freeze from the outside in, with the center-top being the last to freeze (before the glass cracks). But I wouldn't expect it to be simple - depending on the solution and purity of the water before adding the solute, and the thickness of the glass, and the material (and smoothness) of the glass... it can also freeze from the top to bottom. But note that the OP would likely be licking from top; the sweeter part is either in the center or at the bottom. – Luaan Apr 25 '17 at 07:52
  • I'm wondering the concentration of sugar (g/ml) for the eutectic mixture at -4 ℃. When making the popsicles, how much sugar to start with? My guess is that a saturated room temperature solution is what most people use?? Found this https://link.springer.com/article/10.1134/S1070427207020061, but it's a paid for publication. – Stephan Luis Apr 25 '17 at 13:55
  • There may be ingredients other than sugar, as well. In my juice I discovered later that the juice developed a foam when I poured it (not freezing). Could surfactants be affecting the (size scale of) phase partitioning? – Oscar Lanzi Apr 25 '17 at 14:01
  • Re above there's also this phase diagram but no concentrations: https://www.doitpoms.ac.uk/tlplib/biocrystal/water-sucrose.php – Stephan Luis Apr 25 '17 at 14:04
  • This phase diagram that seems to answer the question about sugar concentration https://www.doitpoms.ac.uk/tlplib/biocrystal/water-sucrose.php according to that at -10 ℃ a 60% by weight solution of sugar will not produce that ice (pure water)/ sugar-water mixture. Wow, that's a lot of sugar! Bon appetit! (Although that article is more about frozen cells, yuck!) – Stephan Luis Apr 25 '17 at 14:11