Show HN: Cookoo – Whistle Counter for Pressure Cookers | Hacker News Reader

Show HN: Cookoo – Whistle Counter for Pressure Cookers

s-gv.github.io

34 pointssagargv18 comments

I have noticed that pressure cookers are often not used efficiently. Its quite common to run them on high flame or heat throughout. This is wasteful. Once the water starts boiling in that high pressure, the interiors are a constant pressure constant pressure system. The heat needed to sustain it is surprisingly and significantly lower, just need to cover for the losses. All that extra heat is just heating your kitchen. This is relevant to the discussion because whistle count is strongly dependent on the flame: too high and you would need more whistles, rather counterintuitive. A timer that's set off after the first whistle would be closer to what one needs. Finally too cook fast, set the flame high till the first whistle and then let it simmer

Is the whole whistle counting thing typically an Indian usage of a pressure cooker?

I often see whistle counts mentioned in recipes from the country but all of the more local recipes I have seen relied more upon strict timings.

American here. I've never heard of this usage of pressure cookers, and I'm not sure I really understand it. Can anyone explain why whistle counting works?

Does the pressure-temperature relation of the combined gas law hold in the steam regime, considering the weight clamps the cooker to a maximum pressure? It seems like the whistle frequency would be a function of heat input to the system (or rather heat lost) while temperature would mostly be determined by the letoff pressure value. You'd think a longer time or higher temperature would shorten cooking time, not the amount of heat escaping the system. Below the letoff pressure, temperature is a great proxy for pressure (via the combined gas law), and indeed this is how many of the electric pressure cookers "sense" pressure; they have thermistors thermally coupled to the cook pot. Could it be that pressure recovers to the letoff value more quickly at higher temp? That would make whistle counting for temperature roughly similar to the light measurement method of the modulo camera that was discussed a couple days ago[2]. It seems like the diameter of the pot might impact pressure recovery time though.

All that said, it is GREAT to see more cooking tech, OP. Anything that helps people to cook more (or better) can only be a good thing.

Perhaps worth knowing is that there are three types[1] of pressure cookers, and it seems like OP's product could only potentially work for one (?) of them: old-school weight-clamped. Fagor-type pressure cookers release steam constantly, old-school weight-on-top pressure cookers release steam intermittently, and Kuhn Rikon pressure cookers release no steam at all (best for flavor since no volatiles are lost to the kitchen with escaping steam).

1. http://www.cookingissues.com/index.html%3Fp=2561.html

2. https://news.ycombinator.com/item?id=10053691

By that reasoning determining cooking time by the number of whistles would be a very coarse and inaccurate measure of "time spent at optimal cooking temprature" very sensitive to heating temperature.

If the weighted valve and letoff system is succeeding in staying close to a constant pressure/temperature surely a simple timer would be a better solution.

Yes, the whistle counting thing is typical in usage of pressure cookers in Indian cooking (I am an Indian).

Yes it is, I think primarily because of the design of popular makes of pressure cooker in Indian (Butterfly, etc.) which have not advanced as much as in Europe. After a lifetime of the old whistle style of pressure cooker I finally convinced my wife to try a new style with a pop-up pressure indicator (Fissler Vitaquick - highly rated by America's Test Kitchen) and she finds it miles better, and quicker, than the old style. Not only that, no risk of exploding pressure cookers (as is common in Indian households). I'm still struggling to convince friends and family - who still go to the local Indian store to buy pressure cookers made "back home" when their own "explodes".

I didn't know that this is how other pressure cookers worked.

Mine just releases steam constantly through a valve once it gets to a certain temperature/pressure... but I might just be using it wrong :P

You might have blown your safety valve, pressure cookers aren't supposed to do that.

I think your safety valve is gone. The safety valve should not be releasing pressure constantly once the whistle is on top of the lid.

That's not necessarily true; there are three types of popular pressure cookers[1]. Fagor-type pressure cookers release steam constantly (this could be the kind GP has), old-school weight-on-top pressure cookers release steam intermittently (this may be what you have in mind), and Kuhn Rikon pressure cookers release no steam at all (this third type is best for flavor since no volatiles are lost to the kitchen with escaping steam).

1. http://www.cookingissues.com/index.html%3Fp=2561.html

Correction: They release steam if they are over-pressure, but that's not supposed to happen in normal cooking conditions

Just because you have had a different experience, doesn't mean he is wrong. There are several types of pressure cooker. For example the one my mother used had a weighted thing that sat on top and vented near constantly. Rocking back and forth the whole time.

It's neat to see someone solve a problem that you didn't have any clue existed in the first place.

I have a pressure cooker that I've never used. Am I understanding (from the rest of this thread) that I could be attempting to make some sweet Indian dishes with it?

Would it be possible to release the PCB and schematic source files?

They are in the repo:

Schematic - https://github.com/s-gv/cookoo/blob/master/schematic/whistle...

PCB - https://github.com/s-gv/cookoo/tree/master/pcb/gerber

These aren't really the source files, because they aren't easily editable. I believe the parent was asking for the KiCad files.

KiCAD files:

https://dl.dropboxusercontent.com/u/53155453/cookoo_kicad.zi...

Not sure if this is the latest version.

If tending the stove is a problem why wouldn't you just buy a digital electric pressure cooker in the first place? They're great.

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