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Stocks and extraction

James_Hoffmann_21713

As someone who thinks about extraction soluble material with water all day long, I can't help but think about vegetables and stock.

Unlike coffee it seems like there is nothing in the vegetables we don't want (in terms of solubles that taste good), so the ideal would seem to be to get as much as possible, as quickly as possible. To that end, I can't help but be curious about how I see a lot of vegetables prepped for stock usage. Surely the ideal would be expose maximum surface area. I would presume that with a normally cut piece of carrot that more flavour is taken from the exterior than the interior? I'm going to assume that there is a great deal of unextracted (therefore wasted) material in the middle of a chopped piece.

If so then why are vegetables not chopped as finely as possible before going into the water? Would using a food processor to prep vegetables, to mince them, not be the most efficient way, allowing a faster and greater extraction of flavour for stock - getting the most flavour for you money?

If I had two pressure cookers I'd run a side by side test. (I'm a little curious whether or not there would be a measurable difference in the refractive index to measure extraction - but this might be me thinking too much like a coffee person)

Hopefully someone here has thought about this, and has a good answer about why we do things the way we do?

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Comments

Laura_Pazzaglia_Simmarano_77236

I don't think there is a "standard" way to make pressure cooker stocks. Everyone has come up with their own recipe and techniques - which are always varied by the cook according to what's on hand or on the menu.

However, I can speak my reasoning for keeping the vegetables whole. Most vegetables only need 5 minutes or less pressure cooking time to be fully cooked. So when you add them to a stock that pressure cooks for 10 minutes (veggie stock), 30-45 minutes (chicken stock) or 60-90 minutes (beef and/or pork bone stock) what do you think happens?

The heat and pressure literally burst the vegetables cell walls open and squeeze out all of the juice into the cooking liquid. As long as the vegetable is "overcooked" this process will happen whether the carrot is whole or whether someone has taken the time and care to make a fine dice. The advantage here is not just the prep time savings but also a clearer stock free of cloudy vegetable matter.

As someone who hates to see waste and can't toss out what APPEARS to be a whole carrot after stock-making I can confirm that what remains of the carrot is a completely tasteless carrot-shaped fiber.

Try it!

Ciao,

L

P.S. You don't need two pressure cookers to do this test. You

can do it sequentially with one pressure cooker and compare the results.

Brendan_Lee_56950

I imagine that this practice was born out of convenience. It's a lot easier to just throw big chunks into a pot and allow time to extract rather than all the extra knife work of chopping things up in pre-food processor days.

I was under the impression that the contents inside of a pressure cooker was essentially still so cloudiness could be minimized with proper siphoning of the stock and further clarified through sieve's and superbags or even agar clarification if you needed a super clear stock.

Tim_Sutherland_52834

MC (2.290-291) discusses size and extraction of flavours - the smaller the better for flavour extraction. The reason they say not to grind vegetables "... is that pulverizing plant matter releases juice, which changes the rates of flavor extraction ..." and the stock will not taste the same as a traditional stock. You can do it but you need to play with the scaling to get the taste to match a traditional stock. If you look at the images of stocks in MC you can see that most of the vege is thinly sliced via a mandolin - quick easy and no food processor/grinder to clean.

Chris_Young_80640

@Jimseven and @Tim — I have thought a lot about stocks. In general, I am all about maximizing the surface area to volume ratio to accelerate extraction. This has generally meant grinding meat, thinly slicing vegetables, and so on. Sometimes, however, convenience trumps everything and it's just easiest to throw the roast chicken carcass into my pressure cooker and call it good.

If, however, you really want to maximize extraction and create an amazing vegetable stock, then I advocate one of two approaches:

(1) roast your vegetables, then juice them, then strain through a very fine sieve (or centrifuge if you can). Adjust with water as needed and season to taste.

(2) Juice raw vegetables individually, cook the juices separately, strain and then blend the cooked juices to the flavor profile you like. Season to taste.

Both of these approaches work really well, but you really have to rethink the ratio of the various vegetables. You'll also want to play around with infusing herbs and spices much like you would a teasan after you prepared the base stock.

James_Hoffmann_21713

@Chris Interesting! Worth a little experiment too, though I am loathe to buy a juicer. For clarity - when you say very fine sieve, can you give a range in microns? (Obviously there is a point where things are too fine....)

Chris_Young_80640

@jimseven — with regards to sieving, it really depends on how clear you need things. I would probably be using something around 200 microns.

Sumit__65166

i wonder if you can make stock in coffee syphon. vegetable juice in bottom and fresh herbs in top...

Brendan_Lee_56950

Check this out @sumit

http://youtu.be/B-r3Ma44pCk

Laura_Pazzaglia_Simmarano_77236

For some reason I'm not getting the notifications of replies here - even though I turned notifications on.

To counter @tim southerland, who quoted the MC extraction chapter, if I remember correctly they are talking about flavor extraction in conventional cooking - not pressure cooking.

Here is an example of how much juice the STEAM of a pressure cooker can squeeze out of whole berries:
http://www.hippressurecooking.com/pressure-cooked-blackberry-italian-sodamaking-fruit-extracts-or-steam-juicing-under-pressure/

The yield and intensity will increase when boiling vegetables or fruit under pressure. For example, strawberries only need a minute in a pressure cooker jam recipe - to get ALL of their juice out (no macerating, no slicing or dicing)!

Ciao,

L

Chris_Young_80640

@hippressurecook — Nope, I wrote that chapter and can definitely say we were talking the importance of surface area relative to volume for pressure cooking (and generally any other method of extraction). Back when I was at the Fat Duck, we did a large number of experiments with pressure cooked stocks and our best results came from pressure cooked stocks that had all vegetables sliced as thinly as possible and all meats ground.

An experiment worth trying is with chunks of meat versus ground meat cooked in a pressure cooker. The chunks of meat will still taste like, well, meat after a couple hours of pressure cooking. The ground meat, well, it tends to taste like cardboard. That's a nice indication that you've done a more complete extraction.

Laura_Pazzaglia_Simmarano_77236

Thanks for clearing that up, Chris!

Ciao,

L

Laura_Pazzaglia_Simmarano_77236

@chris It comes down to the density of the food and cooking time - where carrots and strawberries only need minutes to taste like cardboard meat needs more. You make a compelling case for using ground meat vs. chunks. Blumenthal's fussy pressure cooker stock, for example, involves adding vegetables and herbs at different intervals to keep certain flavors intact.

However, I agree that dumping a chicken carcass and veggies and making it go is sufficient for a stock that isn't planning to be the star of the show - and infinitely superior than what you could extract from a cube or can. ; )

Ciao,

L

richardandrichardsen

Surface area is a consideration but not the only one. Some vegetables like onions, leeks and celery are best extracted for 45 minutes to an hour. After that they be decompose and become bitter. Since those are used in stock making and most stock recipes in order to extract the meat thoroughly recommend hours of extraction I image using large chunks adds time to the vegetables point of souring. I place my vegetables in a nylon fishnet when making stocks and remove them at an hour to an hour and one half. Then extract the meat much longer.

If you use a pressure cooker as mentioned below cloudiness is minimized because the internal pressure raises the boiling ( vapor point ) of water above the pots temperature. No boiling is had. When done let the steam off gently ( a passive do nothing until cool technique is best ) to ensure you don't create a "tempest in an instapot" and dirty the stock.

There are filters used by painters, painter's socks, made pf PTFE and ABS that scale down to 1 micron. 20 microns usually will clarify a stock sufficiently unless a consume like broth is needed. In which case successively straining through ever finer filters until 1 micron is reached will clean up just about as well as a protein raft or syneresis. If you need a 100 % solution with no colloidal presence you'll need a centrifuge.