In the mean time, I started to make a sukumo fermentation vat experiment. It is ideal when the vat is kept ~25degrees. As it is summer now and the room temperature can be around 25 degrees, I decided to do this experiment now (end of August 2024). I watched a lot of tutorials videos about how to make sukumo vat (it is called 藍建て in Japanese and one can find youtube video tutorial online) and I take some average recipe and methods from few tutorials.
First, I need to make pot ash water. It is a clear part of water mixed with wood ash. PH of this water is high (basic/alkali) and many recipes use this as alkali water for vat. It was a challenge to find wood ash in the middle of summer in Berlin… I got a tip from a friend and got the ash from a restaurant called ITA Bistro who specializes in wood oven grilled food. They were very nice to give me some of the stored ashes from their oven. They keep them as some gardeners need them as a fertilizer.
Cook a large amount of water on a pot and boil it for a while. This is to reduce the amount of oxygen devolved in water. The indigo vat is a REDOX process, so you want to introduce as less oxygen as possible in reduction process (which is the vat). The ash I got from the restaurant had some charcoal in it, so I used a sieve to filter out charcoal. The second batch had charcoal in it (as an experiment) and was a bad idea as they float on the surface. After a day or so, the water becomes clear and all the ashes stays on the bottom. PH meter shows 10.5, which is pretty good.
I used the amount ratio that was on the Awa Natural Indigo book by Miyoko Kawahito. The original recipe for 75L vat is:
Shikomi (starting point):
Sukumo – 8.4kg
Lye (pot ash water)- 36L
Slaked lime (Calcium Hydrate) – 150g
Sake – 270cc
Nakaishi (middle point, after bubbling starts):
Slaked lime (Calcium Hydrate) – 90g
Kasaage (increasing the liquid mass):
Lye (pot ash water)- 30-35L
Tomeishi(finishing):
Slaked lime (Calcium Hydrate) – 60g
My vat container is 18L, and I have 1.5Kg of sukumo that I bought from Japan… (here is the online shop link). So I recalculate the amount I need accordingly. I bought sake from local Asian super market.
Sukumo has a very specific smell, even when it is dry. you can see/smell that it is a compost material. I poured some warmed pot ash water and start mixing them.
After the sukumo getting softer and clay like, I added the whole amount of Calcium Hydrate Ca(OH)2 and mix it well. Then add the whole amount of sake and mix it well again. This point, the sukumo mix looks very black and smooth. After I added Calcium Hydrate, it also started to smell ammonia like.
I”m using this glass container as vat as I wanted to see the vat from the side as it develops. I happen to have this glass container as we used it in another project. I am not sure if the glass was a good choice for vat as it is fragile and also does not keep the heat well. Many tutorials are using plastic containers as vat. The traditional vat are made of ceramic.
The mixed sukumo is placed inside the container now.
I added pot ash water to about 1/4 and mixed well. Ph is now 10.76. Some tutorial said it is better to maintain Ph11 at the beginning (probably by adding more calcium hydrate) but I decided to leave it as it is.
Here, in retrospect, I made one mistake. I did not heat up the pot ash water to very high temperature as I was afraid to kill the good bacteria living on the sukumo with hot temperature. This was wrong. The bacteria which is responsible of composting the sukumo and what we want to promote in the vat fermentation can live in the 70degrees environment. So it is actually good to pour hot water (around 70 degrees) to activate the bacteria we want and also to kill other unwanted bacteria. I will do this next time I make a sukumo vat.
I made a lid out of two cork pot holders (which became too tight after using it due to moisture.. and I had to adjust its size few times), and a cover out of molton fabric to shut the sunlight going into the vat. I am not sure if this is a good choice. It is all experimental.
From this point, I mix the vat every 3 hours during the day time.
On the day2, I added some more pot ash water (hot) to increase the water amount to about the 1/3 of the container.
5 days later, it is still not bubbling on the surface. Not sure if I am doing something wrong. The Ph is staying around 10.5. On the 3rd day, it was reduced to 10.3 so I added a spoon full of calcium hydrate. Since then the Ph stays around 10.7. The first days, it smelled strongly ammonia like, and it started to change more into earthy compost like smell with hint of ammonia. Also, in the morning, I see some shiny purplish layer on top. This maybe a good sign?? The mixing stick is slightly coloring to blue so maybe something is happening very slowly?!
Day 8: still no bubbles. but even my Ph meter tip is getting blue. I decided to do dye test and dipped a piece of cotton… no blue dye yet.
I watch the tutorial video once again… and feel like the liquid I have is a bit too thick? so, I decided to add some pot ash water (normally they do this after you start to see the bubble). I added very hot pot ash water to about the 1/2 point of the container. I also added calcium hydrate (two spoons) and sake (~80cc). Now the Ph is 11.
