Concentrated birch sap
Birch sap concentration
The Brix value of birch sap is usually in the range 0.5-1.5%. Birch sap Brix value shows the percentage of dissolved substances in the sample. In birch sap most of the dissolved substances are sugars, so the Brix approximately indicates the amount of sugar in the measured samples. As the solid matter of the birch sap is relatively low it would be reasonable to remove water before transport of the product to reduce shipping cost. Compared to conventional heat-treatment process, reverse osmosis has lower operating cost and the ability to avoid heat-treatment processes, which makes it suitable for heat-sensitive substances (e.g. proteins, enzymes).
In addition to water purification and other application reverse osmosis is well known in food industry (e.g. juice concentration). The main idea of reverse osmosis is that liquid is conducted through semi-permeable membrane that removes ions, molecules and other particles from water. The pore size of reverse osmosis membrane is 1-0.1 nm. This means that reverse osmosis enables to filter out everything else except water molecules (Figure 1).
Figure 1.Simplified scheme of reverse osmosis process.
In maple syrup production reverse osmosis helps to remove water before traditional boiling of maple sap. Reverse osmosis can remove up to 90% of water. The effectiveness of the reverse osmosis depends of the machinery used, the condition of membrane and the solid matter content of the sap that is being concentrated. Figure 1 shows that only water is removed from the birch sap – this means that sugars, acids, minerals, proteins, enzymes and everything else dissolved in the birch sap remains in the concentrate. The removed amount of undissolved solid matter depends of the pre-filter(s) used before semi-permeable membrane (e.g. microorganisms can be removed with microfiltration).
Usage of birch sap concentrate
Reverse osmosis removes only water from birch sap. This means that to recreate birch sap from birch sap concentrate purified water that has passed also reverse osmosis step is needed. Used water has to be odorless, tasteless and must be in compliance with the WHO Guidelines for Drinking-water Quality (http://apps.who.int/iris/bitstream/10665/44584/1/9789241548151_eng.pdf). For recreation of birch sap with Brix value one the following formula can be used:
Conc. – amount of concentrate needed, L
Total – amount of birch sap needed, L
B.conc. – Brix value of birch sap concentrate
If the total amount of birch sap to recreate is known and also the amount of concentrated birch sap needed for that is calculated, it is easy to calculate how much purified water is needed to add additionally (Needed water = Total – Conc.). If birch sap with different Brix value is required then the calculation must be changed accordingly.
Storage of birch sap concentrate
The best option for birch sap concentrate storage is freezing (approx. –18 ºC). The birch sap concentrate obtained by reverse osmosis process should be frozen within few hours to guarantee the highest freshness of birch sap that will be obtained during recreation process. Birch sap concentrate could be also pasteurized, but in this case there will be effect of heat-treatment to the birch sap.
Before recreation of birch sap the frozen birch sap concentrate should be melted as fast as possible and needed volume of concentrate measured. Good manufacturing practices (GMP) should be followed at each production stage to be sure that birch sap recreation from birch sap concentrate has storage time similar to fresh birch sap.
Rain Kuldjärv,
Project leader, Center of Food and Fermentation Technologies
Ph.D. student, Tallinn University of Technology
