Get the Offline ArchiveFree lifetime updates

Keeping salt dry

4 min read

Parent
📦
Storage & Distribution
Current
🏺
Keeping salt dry

Keep salt dry by purifying it first, draining the bitterns, and storing it in sealed containers off the floor in the driest place available, because pure sodium chloride only starts to absorb water from the air above about 75% relative humidity, whereas the magnesium and calcium chlorides left in poor salt do so at around 30% to 33%. The clumping the parent article blames on moisture is mostly those impurities, and dry rice in the container is no substitute for clean salt.

Part of Salt Production & Sourcing

Keeping salt dry is the control of moisture uptake and caking in stored salt, which depends on the purity of the salt and the humidity of its surroundings.

Salt Is Hygroscopic, But Not Equally

The parent says salt is hygroscopic and absorbs moisture from the air and clumps. That is true of crude salt; the detail matters because it tells you where to put your effort.

Every salt has a humidity at which it starts to dissolve in the water it takes from the air, the deliquescence point. Sodium chloride’s is about 75% relative humidity at room temperature (a standard handbook value; recalled). Magnesium chloride’s is about 33% and calcium chloride’s about 30% (also recalled). Indoor air is often well above 33% and often below 75%, so:

  • Clean sodium chloride stays dry in an ordinary room most of the time and only gets damp in a humid season, in a cellar or beside the sea.
  • Salt with bitterns in it draws water from the air under ordinary indoor conditions and turns damp, the magnesium and calcium chlorides dissolving first and wetting the surface of the crystals around them.

When the damp salt later dries, the dissolved material recrystallises at the contact points between crystals and bonds them into a cake. So caking is mostly a purity problem that shows up as a humidity problem. The cure is the washing and draining steps in Removing impurities and bitter minerals, not a stronger container. Fresh salt piled on a slatted floor drains its bitterns over days.

What The Parent’s Tips Do

  • Sealed containers (clay crocks with lids, glass jars, sealed wooden barrels) keep the salt away from room air: sound advice. Glaze the clay or use glazed pots, as unglazed clay is porous.
  • Driest location, elevated off the ground: good, since stone and earth floors wick moisture (Moisture Barriers is the food-store moisture barrier article).
  • Dry rice or corn in the container: this absorbs some moisture, but it holds water itself and can mould, sprout or attract insects if it takes up more than it can hold. If used, change it often and keep it from touching the salt you will eat. A reliable seal and clean salt do more.
  • “Salt does not spoil”: true of pure salt, but salt takes up flavours and dirt, and corrodes iron containers, so store it away from metal tools and in non-metal vessels.

What You Need

  • Purified, drained, dried salt
  • Sealed non-metal containers with lids, glazed clay, glass or sealed wood
  • A raised, ventilated, dry shelf away from floors and outer walls
  • A way to check humidity: a damp-test dish (a spoonful left open) will do

Method: Store Salt So It Stays Loose

Step 1: Purify and wash the salt, drain it on a slatted surface for several days and dry it completely.

Step 2: Fill containers to the top to leave little air, and seal them.

Step 3: Put the containers on raised shelves in the driest room.

Step 4: Check a sample monthly; if it is damp or caking, re-dry it, then find the leak or the impurity.

Step 5: Open one container at a time and reseal.

Common Mistakes

  • Storing damp salt. It cakes into a block.
  • Using iron or tin containers. Salt corrodes them and picks up rust.
  • Leaving the lid off a working container in a humid kitchen.
  • Relying on rice instead of purifying.

Safety

Keep food salt separate from everything else that looks like it

A dry white powder in a plain jar is easily mistaken for something else, and salt for food must never share a shelf or container style with curing premix, lye, saltpetre, lime or cleaning powders. Label every container, and keep food salt in containers that are never used for anything else.

What’s Next