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Indigo First Harvest 2020: Step 4

August 31, 2020

If you're just joining in, make sure to start with the Step 1 post to get the outline of the process I'm using.

Step 4: Straining and Rinsing

Once the indigo is alkalyzed and aerated, and I am satisfied that the indigo has settled to the bottom of the tank, I strain off as much water as I can. From time to time, the indigo becomes unsettled from the bottom of the tank, and I will walk away and wait for it to settle again before continuing.

Once I've strained most of the water off, I stir up the tank to get the indigo off the bottom, then pour it into a homemade straining frame to strain the rest of the water out.

This is a large straining frame. For the amount of indigo I am processing, I found it necessary to have a larger straining surface. This is just scrap wood made into a frame, with some window screen stapled to the bottom.

I've also just clamped fabric to the top of a bucket or barrel for straining, which works just as well.

The fabric is a heavy synthetic dress fabric from JoAnn Fabrics. It's thick enough that one layer will keep the indigo from falling through.

Next, when the indigo is strained down to a sludge, I rinse the indigo off of the straining fabric. I then pour the indigo water through a fabric that is finer than mosquito netting, but still porous enough to let the indigo through. I find window sheer fabric works well for this step. This gets rid of leftover plant matter and grit.

	I rinse the indigo off the fabric in a couple buckets of fresh water. I use as many buckets of clean water as it takes to get all the indigo off the fabric.
	I use two layers of the window sheer fabric; it seems to help catch extra grit if there's two layers. I make sure I have a bucket/trash can large enough to add extra water as I am rinsing everything out.
	I pour the indigo I just washed off the fabric through this mesh.
	Once this is done, I use more fresh water to rinse the indigo stuck to the fabric and sludge.
	What was left behind. This is just plant matter and grit I can toss back into the garden.

Then, I add a couple glugs of vinegar to my bucket. This helps neutralize the indigo and remove excess lime. I stir it in well, then let it sit for 15 minutes or so. I stir it again, then pour it onto my straining frame again.

I don't really have a measurement, I just add a few glugs of vinegar in and let it sit 15 minutes. This is a bit like removing calcium deposits from household faucets and appliances. In this case I'm neutralizing excess lime (aka calcium hydroxide or calx) from the indigo.

I repeat the straining process one more time. I put the straining fabric back on my straining frame, and pour the vinegar-rinsed indigo onto the straining frame.

I rinse the indigo off of the straining fabric in more fresh buckets of water, through the window screen sheer fabric one more time, then pour the rinsed indigo back onto the straining frame. I don't use vinegar the second time.

Straining again after the second rinse.

Looking good!

You can repeat the rinsing process as many times as you want. Each time you will lose some matter (including indigo), but your indigo will become darker and more neutralized. I am happy with rinsing the indigo twice, once with vinegar.

Once your indigo is strained, you can either store it as a thick paste in the refrigerator, or let it dry out completely.

	Last year, I strained my indigo over a barrel and collected the paste.
	This year, I am drying the indigo out to store as powder.
	Keeping in mind that this is the first cutting, I know that subsequent cuttings will produce a lot more indigo.

Refrigerated indigo will last a long time, a year or so (I have some that's over a year old). However, if you keep it long enough you may find yourself scraping mold off from time to time (you can still use moldy indigo for a dye vat, just scrape excess mold off).

Dried indigo does not expire or mold, but requires a little extra effort to rehydrate. To rehydrate, pulverize it in a coffee grinder or mortal and pestle, then pour the powder into a bottle partially filled with marbles and water.