Knowledge resources relating to the development of natural products based on the resources of the Kolarctic region.
A review of the uses of tree saps has been made by Svanberg et al (2012); “Uses of tree saps in northern and eastern parts of Europe“, Acta Societatis Botanicorum Poloniae 81 (4) 343-357. This summarises the customs in different countries in the region for using tree sap, and notes that the activity was formerly more widespread, but has remained an important activity in Russia, Ukraine, Belarus, Estonia, Latvia and Lithuania. The article notes that there has been “a resurgence of interest in urban settings through niche trading (delicatessen, health food shops, etc)”
Birch sap has primarily been used as a refreshing beverage, but has a shelf-life of only a few days. Medicinal use of birch sap has formerly been suggested in the treatment of anaemia, arthritis, kidney and liver stones, gout, rheumatism and colds. It has also been used for hair and skin care. However there is little in the way of clinical evidence on the health effects of birch sap.
The seasonal variations in the chemical content of birch sap has been studied in Finland by Kallio & Ahtonen. Information is given regarding the changes in the concentration of the sap over time, with regard to obtaining the best sap quality for commercial purposes. No differences were observed between Betula pendula and Betula pubescens, and the main acid present was identified as malic (also present in apples). The acid concentration increased from 0,1 to 0,6 g/litre over about 4 weeks in April, and dropped quickly in a few days in the beginning of May. The measurements were made in Aulanko Natural Park in Hämeenlinna, FInland (61° 02′ N 24° 28′ E) and differences in timing can occur at other latitudes and with possible with global warming. The sugar content is reported to increase from the ground up to a certain height (around 4 m), then decrease again towards the top of the tree. Sugar contents of up to 10 g/litre were measured, and the main sugars (glucose and fructose) reached their maximum values typically at the end of April or beginning of May.
- “Seasonal variations of the acids in Birch sap“, Kallio, H. & Ahtonen S., Food Chemistry 25, 285 – 292 (1987)
- “Seasonal variations of the sugars in Birch sap“, Kallio, H. & Ahtonen S., Food Chemistry 25, 293 – 304 (1987)
- “Identification and seasonal variations of amino acids in birch sap used for syrup production“, Ahtonen, S. & Kallio, H., Food Chemistry 33 (2) 125-132, (1989)
Development of a probiotic fermented beverage from birch sap is described by Semjonovs et al (“Development of birch (Betula pendula Roth.) sap based probiotic fermented beverage“, International Food Research Journal, 21 (5) 1763-1767, (2014)). The objective was to evaluate the suitability of birch sap as a non-dairy probiotic functional beverage, containing Lactobacillus reuteri bacteria. Fermentation can increase the shelf-life of the product, . It was found that birch sap gave good growth of all bacterial strains examined, with the pH falling from 6 to 4,2 to 3,2. Improvement in the growth was obtained with supplementation with peppermint or malt extracts (at 2% concentration), indicating growth was not limited by carbon, but possibly by other growth factors (such as nitrogen).
Other reference material
 Kim, J.H. et al “Storage life and palatability extension of Betula platyphylla sap using lactic acid bacteria fermentation“, Journal of the Korean Society of Food Science and Nutrition, 38 (6) 787-794, (2009).