Why Can't I Get That BIR Taste & Aroma?

[natterjak]

Ive been thinking about the hypothesis of a large cooking pot making a difference, and although I dismissed it initially, maybe it bears closer scrutiny. They do say "cooking is chemistry" and in chemistry you obtain different reactions under different conditions of temperature and pressure.

Now the pressure in a liquid is equal to the density X the acceleration due to gravity X the depth of the liquid (thanks Wikipedia!) and so in a pot full of base sauce the pressure is proportional to the height of the pot. In other words restaurants cooking in a big 40 litre pot 70cms tall could be boiling their base at double the pressure of you and I with our puny 6 or 8 litre stockpots at home.

From schoolboy physics: Higher pressure -----> higher boiling point. So the base sauce at the bottom of the restaurant chef's big pot could be making different chemical reactions to those which we achieve at home.

I'm not saying it's necessarily true, just that it's feasible. Worth a thought anyway, should anyone be interested in this forum's primary purpose this fine Yuletide night.  But the latest argument thread has more page views and three times the replies in one day than this one has achieved in nearly two weeks. Shame.

[Peripatetic Phil]

Right.  But BIRs don't (AFAWK) use pressure cookers. So could we not replicate the effects of a larger vessel simply by using a pressure cooker (as I already do) ?

** Phil.

[natterjak]

Possibly Phil. Perhaps someone good with maths can put some numbers to the problem, to compare the pressure in a domestic pressure cooker to that at the bottom of a large (restaurant sized) cooking pot and report back?

It's a bit beyond me at this time of night.  It's slightly different in any case because in a pressure cooker there's equal pressure throughout, whereas in a large pot only the bottom reaches max pressure. Mind you, that's where the heat is directly applied and so presumably is the source of any interesting chemistry which is going on.  I'm off to bed now

[George]

Lastly, just for a laugh....
- there's a secret ingredient "they" are not telling us about 

I don't think this point should be dismissed as 'just a laugh'.

My best suggestion is that nobody, so far, has presented a decent recipe which, if followed carefully, will produce results equal to the best BIRs. Why should the best BIRs give away their precious recipes, whether it be in written form or via a youtube video? It could be secret ingredients but my hunch is that it's more likely to be techniques which are simplified or dumbed-down a bit for presentation to us lot. I'm still working on my recent breakthrough. It produced flavours as good, or almost as good, as any BIR, and I've managed to repeat it now with very few ingredients. But when I added a few extra ingredients like fresh coriander and a bit of lemon juice, the flavour went downhill. "How can this be???" I'm asking myself. I need to do more work to understand what's going on.

[Peripatetic Phil]

It's a bit beyond me at this time of night.  It's slightly different in any case because in a pressure cooker there's equal pressure throughout

But is there ?  Atmospheric pressure is experienced equally (modulo epsilon, for vanishingly small epsilon) throughout the liquid in a container; the extra pressure experienced by the lowest part is the sum of atmospheric pressure and the (effect of) the weight of the the liquid above.  In a pressure cooker, exactly the same situation obtains, except that it is not atmospheric pressure that is experienced equally throughout but an artificially raised pressure.  There is still (the effect of) the weight of the liquid above the lowest layer, which will make the lowest layer experience once again a higher pressure, will it not ?

** Phil.

[Cory Ander]

From schoolboy physics: Higher pressure -----> higher boiling point. So the base sauce at the bottom of the restaurant chef's big pot could be making different chemical reactions to those which we achieve at home.

Perhaps someone good with maths can put some numbers to the problem, to compare the pressure in a domestic pressure cooker to that at the bottom of a large (restaurant sized) cooking pot and report back?

Interesting and innovative thinking NJ!  Something I've not considered as a possible rationale before.

If my physics and maths don't desert me, I deduce the following:

• Standard atmospheric pressure is about 100,000 Newtons per meter squared
• A pot of water, of 1 meter cubed (pretty big, for a pot of curry base, I know!), weighs about 1000kg
• The pressure, at the bottom of the 1 meter cubed pot of water, would be about 1000kg x 10 meters per second squared (i.e. acceleration due to gravity) = 10,000 Newtons per meter squared
• Therefore, the additional pressure, at the bottom of the pot, would be about 10% of the standard atmospheric pressure
• Therefore, if a typical pot, in a BIR, is filled to a depth of 50cm (assuming it is water), the pressure, at the bottom of the pot, would increase by about 5%
• Alternatively, the pressure, at the bottom of the pot, would increase by about 1% for each 10cm of depth of water....so by about 1% for a small batch of curry base with a depth of around 10cm

As I understand it, pressure cookers operate at a pressure of around 2 standard atmospheres of pressure? Which is about 10 times the additional pressure at the bottom of a 1 meter cubed pot of water.  And around 20 times the pressure at the bottom of a typical BIR pot (assuming it is 50cm deep).

Is my maths correct?

Either way, as it stands, a pressure cooker is pressurising far more than a big pot of curry base.  But who can say whether this is significant or not?

Three things for me to do, then:

• Cooker a large pot of curry base (60 litres or so) for long times (3 hours or more)
• Make a curry base using a pressure cooker (time to buy a new one!)
• Compare the results with my normal, small scale (2 litres or so) curry base cooked for relatively short (1 hour or so) times

Thanks for the insight NJ! 

[Peripatetic Phil]

This graph shews clearly how boling point (of pure water; mixtures of water, oil and spices will clearly differ) varies with pressure.

[natterjak]

Thanks CA & Phil for helping develop this thought. You are of course correct the pressure is the sum of atmospheric pressure and the pressure due to the head of water. CA I agree with your figures although my derivation was slightly different. I just googled "pressure in water per metre in atmospheres". Plenty of sources confirming that per metre depth the pressure goes up by 10% of an atmosphere.

I've also cross checked on pressure cookers and at a typical 15psi they are indeed at 2 atmospheres, which from Phil's graph is a boiling point of just over 120 deg C.

So the marginal increase in boiling point due to the height of a restaurant cooking pot looks to be rather modest in fact, so maybe it's not all that significant. Worth thinking about though.

[Whandsy]

I'm sure one of our members has recently tried a full size base, and commented that the flavours were still missing! Can't remember who though. I think it might have been Haldi??

W

[Kashmiri Bob]

I think the BIR aroma is most likely down to high temperature and the consequent molecular changes in oil composition.  Chris posted recently and nailed it using high powered heat with his outside burner.  The CT madras sauce I made not long ago also had the aroma in abundance; lid on, high temp, and under pressure (albeit minimal).  The pressure cooker could be the way forward (remember what Julian said re: that smell).  Perhaps a curry could be finalized in one?  Whilst its unlikely that BIRs, TAs, etc. use pressure cookers much, they don?t use domestic hobs with limited heat output either.

Rob