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Druce Batstone

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since Jan 30, 2014
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Recent posts by Druce Batstone

Welcome Peter. I am an active domestic fermenter with a background in chemical engineering. I recently purchased "The Noma Guide to Fermentation". The book is fantastic.

There is very solid information on the fundamentals and even more on techniques that can be used to replicate the ancient methods.

Miso for example is a long process. let me quote;

Miso is a fermented paste made from a mash of cooked soybeans, koji and salt. Like vinegar, miso is a two-stage fermentation. First the fungus Aspergillus oryzae is grown on either rice or barley to produce koji (read the koji chapter page 211) for a deeper understanding of this process). Then the powerful enzymes produced by koji, namely protease and amylase, are harnessed to dismantle the protein and starch in another substrate (traditionally soybeans), cleaving them into amino acids and simple sugars, respectively. Wild yeast, lactic acid bacteria and acetic acid bacteria also add to the fugue of flavours as the miso ages.



I think this quote answers your question.

Druce
3 months ago
After the comments in this thread, I would rethink the all insulating castable rocket stove if I was ever to make another. There would be two castings - the lower section from dense castable (reinforced with stainless steel needles) and the riser from insulating castable. Both would have wall thickness of about 25mm. I would try to incorporate Peter Berg's trip wire and back corner curve in the dense castable (how I wish I could go to a workshop run by Fox).The two castings could be held together by 25mm of insulating board on all surfaces. I would still use a steel frame to hold everything together and for mounting the oven.
8 months ago
Re Dense and Insulating Castable Refractory


These are supplied in bags but do not have Portland cement in the mix. Have a look at a Perth based supplier www.woodfiredpizzaoven.com.au/refractory-materials/refractory-cements/insulating-render

As mentioned, the insulating refractory is normally used as a backing layer. I think it would be quite durable in all parts of the rocket stove. The cost per bag is much the same for dense and insulating but the volume is about twice for insulating.


8 months ago
Here are some answers from a test firing yesterday.

I used a 5kg log split into kindling. The oven reached 250 C in 15 minutes and 300 C in 30 minutes from ignition. The maximum temperature was about 320 C (just off the scale in the cheap oven thermometer). There was no cooking involved. The temperature dropped by about 20 C when the door was opened in normal cooking mode. The temperature of 320 C was very stable for more than an hour when finally, the 5kg of log was just embers. The kindling was not very straight (knotty log) so I might have got a higher temperature with higher density packing in the fire zone but I think 350 C might be the maximum. I could also improve the transition out of the oven to the stack (two pieces of square down pipe) to get better draft which could increase the maximum temperature.

I purchased dense and insulating castable (Brisbane Australia). Yes I would cast the complete J stove in insulating castable to make it easier to move and to reduce cost. The temperature of the inner surface of the riser should be higher if there is less heat loss through the walls if they are insulated. Not that should have any great effect as you are looking for a chimney effect to achieve draft.

The oven I used is as Fox says - thin steel with insulation. I think there is a Japanese guy with information on the dome setup that Fox has suggested. From memory he used two stoves on either side. If you really wanted to get close to your objective I suggest you consider a larger stove (say 200 mm 8") or two stoves for more flexibility.
8 months ago
Thanks apple givers. I learnt most of what I did from Permies. Hope I can give something back.

Fox, I cast the stove in two halves. Your casting is much better than my efforts. I've been following your thread since the beginning and greatly admire your workmanship and ability to communicate.

I used dense castable for the bottom part of the J for temperature and abrasion resistance. My work experience included specifying castables for wood burners used industrially. The duty requirements turn out to be an order of magnitude greater than short-duration, lower-temperature pizza oven duty. The temperature in the burning zone of the wood burner was high enough to form clinker and the burners could operate continuously. I've seen nothing like this in the fire zone of the Pizza stove. That's why I think insulating castable would last a long, long time.

Sorry about the lack of edits in my previous post. The extension piece reduced pizza cooking times from 12 to 15 minutes to 5 minutes. Your experiments with the fan tells me that the resistance to gas flow through the oven is much less compared to the resistance under your plate. I worried about burn back but was very agreeably surprised how easy it was to get the fire going up the riser. A gentle puff form my old lungs did the job!

The idea of making a stove top appealed to me too but the complications defeated me. You are aware of Matt Walker's work. Have you thought about using the glass cook top?

Cheers
Druce
8 months ago
Ethan
Here's more detail on the repurposed oven on a J tube rocket stove. You seemed concerned about heat loss. I don't think you need to worry. I have not insulated the top or sides of the oven with anymore than what was already in place. The sides are warm to hot of course.

The cooking speed s mainly a function of the quality of the fire not heat loss including door opening. I believe this is a feature of the rocket stove and a black oven. I guess it's possible to do a calculation but intitutively the hot gas flow is very high. The better the fire the more heat in to overcome any losses. Any loss on door opening is soon replaced by hot gas.

You will note a vertical length of 150mm SHS in the fire box. I found this greatly improved the quality of the fire. It creates a "P" channel and allows sticks to stand vertical so more sticks are firing in the base of the fire tube. The time to reduce a pizza was reduced from 1 to 1 minutes to 5 minutes with this modification. I'm sorry that I have yet to measure temperatures. I've just purchased a suitable thermometer and will use it on the next firing. Firing is with spotted gum kindling of about the same length. I doubt if I could get the same results with random diameter fallen sticks and twigs.

The rig can be moved but is still very heavy. I was able to buy an old oxy-acetylene carrier on Gumtree. The frame came from old bed frames. Yes there is a bit of welding but I used the corners of the bed frame wherever possible. The frame is riveted which gives a nice retro look. The oven was free (also on Gumtree). The cost and weight is in the castable refractory. If I was to make another, I would only use insulating castable. This has dense castable in the fire zone but I think insulating castable will withstand the conditions almost as well. I used the recommended proportions for a 6" J stove. Ash accumulates in the fire zone but is easily cleaned by hand when cool. The SHS extension is easily removed. Some fly ash comes up through the riser but very little accumulates in the oven.

You will note that two pizzas can be cooked at the same time. The lower one is on a tile. The top one is on a terracotta plant-pot base.

Hope this helps.

Druce

8 months ago
Ethan wrote

My plan is to use a repurposed electric oven with a RS I will cast using refractory materials.



My advice is to go for it. Attached is a photo of my oven.

Pizza cooking times are now down to 5 minutes.

If you are interested, I can add more information. I had a problem submitting a longer reply to the forum so this is a bit of a test.

Cheers

Druce

8 months ago
Welcome "Felix". North Eastern NSW is a wonderful part of Australia. Seems you will be a good steward of your family's patch.

I'm near Brisbane. Would you be willing to share cuttings of your unusual grape.

All the very best

Druce
11 months ago
My suggestion is to cut back now. I am in Australia in a similar zone. I am cutting old and green fronds now. My son, who lives inland on the same latitude but has more frosts, has more success than me. He reckons that you can slash (mow) the fronds any time and the crowns will keep sending up spears.

Hope we both get a harvest in spring.

Druce  
Jeffrey, the ball in the waste(clack) valve must move for the pump to work. The ball is glass in my pump. At rest, the ball sits in a frame that, from memory, has limited adjustment up and down. With flow in the drive pipe, the ball lifts and seals against thick rubber with a centre hole in the top of the chamber. The sudden stop of flow down the drive pipe causes the "clack". The ball drops, flow resumes and the cycle repeats.

Sometimes the ball would hold up against the rubber with a trickle of water coming out of the top hole. Finger pressure was enough to force the ball down to start the flow in the drive pipe and the pump cycle.

I suggest you remove the flanged plate, lift out the thick rubber and check the clearance of the ball. It sems to me that the ball supporting frame is too high.

Hope this helps.
1 year ago