I'll copy and paste the write-up from /u/ilikeycoffee who did a tremendous job and should be bumped due Reddit's format along with updated info and other people's knowledge to go along with comments that was posted in the @'s original thread:

• https://www.reddit.com/r/DIY_eJuice/comments/3mrqoi/mallow_out_man_a_little_bit_on_marshmallow/

Who doesn't love the taste of marshmallow? Terrorists, the Taliban, ISIL probably. But the rest of us? It brings back fond memories of youth, and most of us love the taste to this day.

Did you know the humble marshmallow started its life as a medicinal substance? It actually comes from a plant, called the "marsh mallow" plant, known as "althaea officinalis". It's been around for a long time too, Egyptians mixed the root of that plant with honey (another wonder liquid I might write up down the road) millennium ago to relieve sore throats. The Egyptians also used the sap from the tree, mixed it with honey and nuts, and used it as one of history's earliest confectionaries (ie candies, sweets).

In the 1800s, food scientists, pharmacists and doctors learned how to efficiently extract juice from the marsh mallow's roots and, when combined with egg whites and sugar, was whipped up into a meringue type mixture that would harden and be one of history's first modern throat lozenges to help kids with sore throats.

So the early marshmallow candy - not what we know today, but a hard candy! So how did we get to the marshmallow we're familiar with today? The soft spongy treat that melts so well? One way was to get rid of the actual marsh mallow sap (though you can still find authentic marsh mallow root marshmallows!) subbing in gelatin instead (and corn starch).

Gelatin's the key because it helped the foam created in making marshmallows to stabilize and not harden down. You end up with a softer candy (though still not the marshmallow we know today - read on!) with a low melting point (compared to hard candies). But making marshmallows via this method was labourious; it took hours per batch because you had to let the candy "sweat" for hours to form the skin, then apply starch. And they were all shapes and sizes, and more dense than what we're familiar with today.

The marshmallow we know of today wasn't really common until the mid 20th century when additional mechanical inventions allowed for the tube-shape marshmallow manufacturing process - long tubes of marshmallow were cooked up, whipped up and shaped, then injected with high pressure air to puff them up, and sliced to create the round, short tube shape we all know today. Kraft Foods even used a space-age term to describe the modern method: "jet-puffed" :D

So the millennium-old marshmallow is actually an invention of the 1950s, if we're talking about the marshmallow you and I are both familiar with. As a side note, only two companies control most (not all) of the marshmallow commercial creation process in the US! Google it up to find out who (cheat: one is Kraft Foods).

On taste, marshmallows are all about texture and little on taste. There is some vanilla since it is used in most recipes for the confectionary, but the main ingredients are gelatin (beef, unless it's kosher, then it is fish-derived gelatin), sugar and corn syrup. Cornstarch adds to the flavour profile subtly, since marshmallows are coated with a fine powder of it.

The real magic of marshmallows happen when it is heated, or better still, when it is toasted! You're basically caramelizing the surface sugars in a marshmallow when you toast it up by the campfire, adding a distinct caramel flavour that plays against the gelatin and corn starch (which also changes a bit in the heat process). Even just melted, things change up - you perceive the sweets more (sweets become more prominent the warmer they are), and as we all know with s'mores, with rice crispy squares and the like, marshmallow loves to play well with other flavours.

Which brings us into vaping recipes and the use of marshmallow flavorings!

First on how the flavourings taste: I only have two marshmallow flavourings - Lorann and FlavorWest. I feel the Lorann is closer to the real marshmallow taste, but without any notes of sugar present - a straight up taste test comes back slightly bitter, but noticeably marshamallow. Diluting 5 drops into 5ml of water shows a bit more sweetness, but I'd call it neutral at best, or slightly bitter still. The FlavorWest variant tastes a bit more chemically to me, though also marginally sweeter. In the 5drop/5ml water test, the chemically aspect is still there. Both should not be treated as a sweetener (IMO) in your recipes. EDIT Other flavour companies' Marshmallow might indeed be sweeter than these two mentioned - try the 5drop/5ml water test yourself to find out!

I wouldn't consider this a "cream" flavour. YMMV. It could be considered a "cream booster" flavour (ie aiding your primary cream note shine through a bit more), or a "cream enhancer" flavour (ie, sum is greater than the parts). Also, this is not your campfire marshmallows, though you could easily recreate that flavour with marshmallow + caramel + sweetener.

I also would never want to vape a "marshmallow" eliquid (ie, marshmallow and nothing but in the mix). Marshmallow to me is an additive, an adulterant, a side note, not anything you want primary. Also, I see a lot of people trying to create the "s'mores" experience in a vape eliquid recipe, but many miss the boat by not having a sweetener along for the ride - graham crackers, chocolate, marshmallow. Those that toss some EM or sucralose in there to help it on its way seem to enjoy higher ratings on ELR. Maybe a tiny bit of vanilla boost too.

Where I think Marshmallow flavourings shine is when they are treated solely as an additive, an enhancer to a recipe, and not as a primary taste you're trying to get. Here's some ideas on using Marshmallow flavour in your next recipe:

If you want campfire marshmallow, you will need caramel and some sweetener. Or buy one of the toasted marshmallow flavourings (I've never tried them!).
Seems to play super well with two creams I have - Bavarian Cream (TPA, FA, FW), and Vienna Cream (FA). Also loves being with Strawberries and Cream DX (TPA), Sweet Cream (TPA). And a bonus - it actually can make FA's Condensed Milk taste ok (that, alone is a miracle).
Seems to love all non citrus fruits. It just mellows them out without hiding them.
Chocolate and Marshmallow - a natural! But lean towards using a sweeter chocolate or a sweetener additive. I tried cocoa and marshmallow once and really didn't like it.
Think of Marshmallow as an enhancer / softener for vanillas you use in your recipes.
Got a nut flavour? (Hazelnut, Walnut, Almond, Peanut yada yada)? Marry that with some marshmallow (again again something sweet) and you got a party going on.
Bananas and Marshmallows were made for each other. Ditto for Cinnamons and Marshmallows. Play around!
I've found that Marshmallow can sub out a portion of coconut! If you don't like coconut taste much, but a recipe requires coconut, try the recipe with half the amount of coconut and half of marshmallow.

I haven't had any real success using marshmallow with tobaccos OR citrus fruits; maybe you will? Share your results!

Well there you go - the humble Marshmallow. The 2000+ year old candy we've only known for about 60 years :D