Marshmallows, beer and even some orange juices are not considered vegan foods. And, depending on one's definition of "vegan," neither are some sugars.
Refined sugar -- the kind that's added to coffee, cookie dough and cake batter -- is made from either sugarcane or sugar beets. The two have near-identical nutritional facts and tastes, and they are used about equally in the States. But, their refining process is different. To manufacture table sugar from sugarcane, sugarcane stalks are crushed to separate the juice from the pulp. The juice is processed and heated to crystalize, and is then filtered and bleached with bone char, which results in sugar's pristine white color.
This is what sugarcane looks like.
Bone char filters are not used to process beet sugar, however, because this type of sugar doesn't require the same extensive decolorization. Instead the beets' juice is removed through use of a diffuser and mixed with additives to make the juice crystalize.
This is what sugar beets look like.
In the U.S., sugar companies use bone char derived from cows for this filtering and bleaching process. To make bone char, animal bones are heated at incredibly high temperatures and are reduced to carbon before being used in a refinery. The sugar does not actually contain bone char particles, but it does come into contact with them. "Refined sugar does not contain any bone particles and is therefore kosher certified. The bone char simply removes impurities from the sugar, but does not become a part of the sugar," Caroline Pyevich reports in The Vegetarian Journal.
It gets even more confusing: While bone char is used to bleach and filter cane sugar, not all cane sugar is refined with bone char. Some companies rely on alternatives like granular carbon, which does not contain animal products, during the filtering process. You wouldn't be able to tell the difference by looking at the sugar or by tasting it, and loose sugar packets and packaged foods with non-descriptive ingredients can make it impossible for a person to distinguish sugar refined with bone-char from its counterpart.
Animal-lovers may assume the solution is as simple as using beet sugar instead of cane, but the two perform differently in the kitchen, making recipe adaptations and substitutions a hassle. Plus, it's not easy to decide which kind of sugar goes into your food when you're not making it yourself.
There are some certified cane sugars that do not use bone char in their processing (check out this list from Peta and this list from The Vegetarian Resource Group). Be sure to check labels (remember: beet sugar will never contain bone char) and contact manufacturers with any questions.