If you live outside the German-speaking world, chances are that you've never heard of Persipan. No, it's not a Pokemon. It's also not one of Dow Chemical's new miracle plastics, nor is it a religion secretly practiced in the mountains of Pashtunistan. Persipan is a baking ingredient used mostly in Germany.
Being in the United States, I've discovered that many people need introducing to marzipan, which is not nearly as popular here as it is in central Europe. For Americans, persipan occupies the next rung down on the ladder of culinary obscurity. I call that rung the "Huh?" Zone. Marzipan, though the citizens of places like Lübeck and Nürnberg might put my face on a wanted poster for this statement, is little more than almond paste and sugar. It's good. It's loved. I bribe my dearest with small gifts of marzipan lest she buy the giant loaf from GermanDeli.com and leave it where I can find it.
Almonds, the key ingredient in marzipan, are not the cheapest of agricultural products despite increasingly vast tracts of Californian real estate being turned over to the cultivation of almond trees. Since marzipan is both very popular in some parts of the world and, due to scarcity and all that market jargon, a bit on the expensive side, cheaper alternatives are always being sought by those powers that make a living selling substitute goods to cheap beggars like yours truly. Like ALDI, possibly the single largest corporate consumer of persipan. Enter also other members of the genus Prunus, which includes plums, cherries, and all sort of other orchard fruit. These are very similar to the almond, with the difference that with all but the almond we eat the drupe, not the kernel. That leaves a lot of kernels destined for the organic waste pile and up for grabs. The name of Prunus persicus, the peach, combines with marzipan to give us... persipan! This despite the fact that the apricot is by far the most common source of kernels for persipan.
The problem with kernels from other Prunus species, apricot or other, is that they're either really hard to get at (when was the last time you cracked open a cherry stone?) or plain poisonous. While the active ingredient, amygdalin, was named after the (bitter) almond, it is present in larger amounts in cherries, apricots, and such. When amygdalin decomposes, it yields prussic acid, which you may also know by its popular name of hydrogen cyanide. This is not a baking ingredient unless you're one of those nutty old hags who make the news by poisoning the whole village with cake. Kernels must be processed and de-bittered before they can be used.
Raw persipan mass, according to industry standards, is 35% sugar and may have a moisture content of up to 20%. It should be stored at temperatures under 18°C and at a relative humidity no higher than 60%. 0.5% starch is required to be added as an indicator in Germany, which is the top producer and consumer of persipan. The indicator means that it will fail an iodine test if it's sold as marzipan, which contains no starch. The apricot kernels are sourced from major Eurasian producers of apricots, meaning places like Iran and China. Retail persipan is closer to 40% kernel paste and 60% sugar, in line with the German regulation that the sugar to kernel ratio be no more than 1.5:1. The sugar itself is the cheap sort rather than the glucose preferred by premium marzipan makers.
The difference in flavour is noticeable but not radically different. Some people don't like the very almondy taste of marzipan and are happy to use persipan as a substitute. Others use persipan because their consumers don't care terribly either way, or because they're selling it in a market where people wouldn't know the difference. Persipan can be used anywhere where the recipe calls for marzipan.
Nutritionally persipan and marzipan are dissimilar. Apricot kernels have been considered as a foodstuff in the past for good reason and indeed serve as an occasional snack food in parts of central Asia. Compared to marzipan, persipan mass is poorer in calcium, vitamin A, and folate but much richer in iron, vitamins B1 and C, zinc, and protein. In terms of calories and fat content, the two are very comparable at around 500 kcal/100g (170 kcal/oz) and 30-35% respectively. Though rich in HDL, neither is a diet food. These figures are before sugar is added to make the finished product.
Unless you're in the *ipan heaven called Germany and have access to it year-round, you're most likely to encounter persipan in a shop in early winter, when the German Christmas delicacy known as Stollen and other baked goods are sold by major retail chains both in Europe and in North America. In items like this I personally like the more subtle flavour and texture of persipan. Ultimately consumers will probably have a choice not related to cost since the demand for persipan has driven up prices for apricot and peach kernels to a level almost on par with almonds. Either way, it's all tasty German baking to me.