Reducing Birch sap to syrup


In my first year of birch sap tapping and syrup reducing, I managed to make 1 litre of syrup.

I think I’ll NOT tell my husband that in that process I evaporated 99 litres of sap into the air of our well-sealed house. We spent 3 weeks living in a sauna trying to reduce the endless bottles of sap that seemed to fill in the blink of an eye; I thought having new born babies was hard work, this was like having lots of hefty, difficult babies all demanding a lot of attention. By the time the last sweet drips of birchy water dripped from the trees I was a wreak, my house was saturated and at risk of being condemned with wet rot.

You might be put off totally having a go at this right now, I was pretty much – BUT when I started using the little bottles of syrup drizzled over roasted cocoa nibs on Sweet woodruff custards, in jellies laced with rosemary and violet flowers, and with birch bitters & gin…

homemade birch sap syrup

Then, just like that, I forgot all the agony of the labour and with starry-eyes, longed for the next birth of Birch.

Then, just like that, I forgot all the agony of the labour and with starry-eyes, longed for the next birth of Birch.

After the sauna of birch disappeared I wiped the final layer of condensation off my computer screen and searched something like ‘ there has to be a better way’ into google.

In the cold tapping lands of Canada, people have developed fantastic ways to extract the sweet from the sap; reverse osmosis pushing the sap at pressure through a semi-permeable membrane so only the water can escape, leaving sap with a 10% sugar concentration. Clever, but perhaps a bit technical & unlikely to come under ‘essential bar supplies’. Other fancy bits of kit include Steam Enhancers, Vacuum Evaporators, Vapor Compressors and Heat Exchangers, they all do the same thing and are all very expensive.

Or, on the other hand people do this: tap a birch tree, put their sap in a bucket, leave it outside in the freezing cold, forget it’s outside, go to bed, wake up in the morning & remember it’s outside, bring the frozen bucket of sap in, thaw it by 1/3rd… Taste it & realise the thawed sap is very, very sweet; in fact it’s probably 10% sugar.

Birch sap trees

No kit required, just cold. Let me introduce you to ‘freeze concentration’. *

It’s exciting and a bit scientific which makes me feel cleverer than I am.. The great thing about this is not only that you’ll not need to live in a cloud, but that you can take advantage of those initial sweet, cooling flavours in sap, without losing them in caramel (You should of course turn some into the dark syrup as well, not to do so would be verging on criminal).

So, now you have sap which is 10% sugar. You can either start reducing this down in a wide pan until it’s a 6th of its original volume to make molasses like birch syrup, or you can freeze the sweet sap again and thaw again, (and again if you’re patient).

The more you freeze and thaw the sweeter the first 1/3 of the sap will be, until it turns into a sensational wild version of simple sugar syrup – but with coolness of xylitol rather than cloying of sugar.


1. You of course don’t need to live in the Arctic Circle to do Freeze Concentration, you just need a freezer.

2. One thing to remember is to leave room for the sap to expand in your bottle as it freezes – only fill bottles by 80% with sap so they don’t burst open in the freezer.

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