Brine boiling makes salt by boiling down water from a salt spring or a brine well in wide, shallow pans, and the stronger the brine the less wood it costs: a nearly saturated brine of about 26.4% needs roughly 12.7 times less water evaporated per pound of salt than seawater does. Find and measure the strongest brine you can reach before you build anything, because a weak 1% spring costs more fuel than the sea.
Part of Salt Production & Sourcing
Brine boiling is the evaporation of naturally salty groundwater, from springs or wells, to leave crystalline salt, using fire when sun and wind are not enough.
The Brine Is The Resource
Seawater is about 2.74% sodium chloride, so making a pound of salt means boiling away about 35.5 pounds of water. A natural brine of 20% needs only 4, and a saturated brine (about 26.4%) only 2.8. The ratio of water to boil is 35.5 ÷ 2.79 = 12.7 times less for saturated brine than for the sea, and the fuel follows it (the worked numbers are in Yield calculations). That is why salt works have historically grown up around brine springs and wells rather than the sea, wherever such brine exists.
The brine can come from two sources: a spring or lick that already reaches the surface (Salt springs and licks), or a well that reaches brine underground (Brine well construction). Either way, measure the strength first.
What You Need
- A brine supply of known strength, in enough quantity: a saturated brine gives about 0.32 kg of salt per litre (worked out in the well article)
- Pans of a metal that tolerates hot brine, wide and shallow (Evaporation pan design)
- A firebox, dry wood, and a chimney or draft
- Skimmers, scrapers and baskets, and a drying place
Method: A Brine Boil
Step 1: Settle the brine in a tank to drop sediment, and strain it.
Step 2: Fill the pan, light the fire and bring it to a steady boil.
Step 3: Skim the scum that rises.
Step 4: Top up with fresh brine as the level falls, and watch the pan for the deposit of scale on the bottom.
Step 5: When crystals appear, lower the heat and rake or scrape them out; drain and dry. Keep the bitterns apart.
Step 6: Purify the salt before eating it (Purification & Grading).
Common Mistakes
- Boiling a weak brine. A 1% brine costs more fuel than seawater.
- Not measuring the brine. Strength drifts with weather and with the level of the water.
- Letting the pan scale up. A crust of calcium sulfate on the base cuts heat transfer.
Safety
Hot brine and contaminated brine
Boiling brine spatters and scalds. Brine from near mines, oil seeps or industrial sites can carry metals, hydrocarbons and other poisons that boiling concentrates; do not make food salt from it. Keep children away from pans and pits.
What’s Next
- Learn next: Evaporation pan design — the pan itself
- Combine with: Fuel efficiency and large-batch processing — getting more salt from each load of wood