Horse Chestnut Viking Soap – is it real?!

The inspiration for the following soap project are two websites, both linking the soap nut Horse Chestnuts to soap made by the Vikings.

http://www.ehow.com/how_6528425_make-viking-soap.html
http://www.iol.ie/~ballyduf/Laura.html

Some observations on the process:
Fresh horse chestnuts are a pain to peel, let them dry for a couple weeks so the flesh will shrink from the outer shell a bit.

Both recipes mention soaking in water for two hours, followed by packing the soft pieces into a mold. Just soaking, in cold or hot water, does not soften the flesh enough to make a bar. To change the consistency of the raw horse chestnut flesh I slow cooked the chunks and found that when they did soften, the surrounding liquid also became gelatinous, as I would expect from a soapy liquid. Unfortunately, this meant the functional saponins were being leached into the liquid and did not stay in the nut flesh, explaining why the starch, which can be shaped into balls, does not really soap very well.

Be aware horse chestnut is slightly toxic, as a laundry soap it should not be a problem as long as the fabric is rinsed well, but I would not use it directly on the skin.

Some observations on the science behind the plant:
The seeds of the Horse Chestnut, Aesculus hippocastanum L., are mentioned as having the highest levels [from all soap berries] of saponin: 260,000 ppm. [1]

Saponins are found in many plants and derive their name from the soapwort plant (Genus Saponaria), the root of which was traditionally used. Saponins are also found in the botanical family Sapindaceae, with it’s defining genus Sapindus (soap berry or soap nut), and in closely related families Aceraceae (maples) and Hippocastanaceae (horse chestnuts). Within these families, this class of chemical compound is found in various parts of the plant: leaves, stems, roots, bulbs, blossoms and fruit. The leaves and fruit of the Horse Chestnut can be used to make a soapy paste or liquid. [2]

All parts of the horse chestnut trees are moderately toxic. The toxicity is due to saponin aescin and glyside aesculin, with the alkaloid possibly contributing. Native Americans used to crush the seeds and the resulting mash was thrown into still or sluggish waterbodies to stun or kill fish. They would then boil or drain the fish at least three times in order to dilute the toxins' effects. [3]

Horse Chestnuts were used in the past in France and Switzerland for whitening hemp, flax, silk and wool. They contain a soapy juice useful for washing linen and milling caps and stockings as well as for fulling woolen cloth. For this 20 conkers where enough for six litres of soft rain or river water. They were peeled, then rasped or dried, and ground into a malt. This malt was steeped in cold water, which soon became frothy, as with soap, and then turned milky white. The liquid had to be stirred well at first, and then, after standing to settle, strained or poured off clear. [4]

Horse Chestnut soap made according to the descriptions

(unfortunately, the solid nut starch does not soap...)

Some observations on the presumed link with Vikings:
Even though Vikings are known to groom and wash, as evidenced by the numerous mentions of said grooming in saga’s and outsider observations, soap is not mentioned in context of personal grooming. As far as I’ve found, some sort of soap is probably used for preparing wool for processing and maybe for cleaning clothes, but I found no actual references to either, only conjecture. [5]

But most importantly: Horse Chestnuts are not native to Europe, they are native to the Balkan Peninsula. [8] The Romans are reported to have brought edible chestnuts back north with them, but Horse Chestnuts did not make it up to northern Europe until the 16th to 17th Century.

Conclusions:
Horse Chestnut fruit is capable of making a useful soapy liquid.

But, there is no connection whatsoever with Vikings, or any other Scandinavian or European cultures in Medieval times, as Horse Chestnuts did not exist in Europe, at least not yet.


Bibliography
[1] http://journeytoforever.org/biodiesel_soapberry.html
[2] https://en.wikipedia.org/wiki/Saponin
[3] https://en.wikipedia.org/wiki/Aesculus
[4] http://www.herbsociety.org.uk/kh-hedgerow-to-kitchen-horse-chestnut.htm
[5] http://www.vikinganswerlady.com/hairstyl.shtml
also of interest: https://www.en.wikipedia.org/wiki/Aesculus_hippocastanum