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Large Volume Stock Production Logistics


Chris Amirault
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If you make enough stock often enough to justify it, you might think about getting a wort chiller (used when making home brewed beer). They work really fast for large volumes of liquid. You might be able to find one a bit cheaper, this was the first one that came up on google.

http://www.northernbrewer.com/shop/standard-chiller-3-8-x25-with-vinyl-tubing.html

Jess

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How long can it keep in the bottom of a very cold fridge?

I've had to wait a week between times when I could work on stock, with no worried as long as it smelled ok, because I process it at the end in a pressure canner--20 minutes at 10 lbs kills even the nasty spores. I've also reboiled and used it after that length of time without the pressure canning step, but wouldn't feed the result to a frail or immunocompromised acquaintance.

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Pressure Cookers : Alter flavor, alter texture and sterilize food.

At low-pressure settings (5-8psi) you get altered texture and quicker cooking. At high-pressure settings (15psi) you get flavor changes as well, both more intensity and new flavors.

Because the way food cooks is affected by both temperature and pressure and boiling temperature is dependant on pressure:

Higher pressure = higher the boiling point = higher cooking temperature.

An oven at 400 F will cook the inside of meat to a maximum of 212 F.

A stovetop pressure cooker at 15psi (the pressure cooker standard) will take it to 250F.

An electric pressure cooker with their lower pressures of approximately 5-8 psi will take it to 227F or 235F.

If you just want to cook your stock or meat quicker use an electric pressure cooker, but preferably a non-venting one like Cuisinart because venting ones vent flavor in the steam rather than retain it.

If you want your stock and meat to taste meatier and more intense you’ll need a stovetop pressure cooker for the 15psi.

Summary:

Electric Venting pressure cookers cook quicker, soften texture but vent flavor.

Electric Non-venting pressure cookers cook quicker, soften texture and retain flavor.

Stove top pressure cookers (standard 15psi units) cook quicker, soften texture and intensify and merge/transform flavor = Alchemy.

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Made a batch of stock in a Presto stainless steel 6-quart stovetop pressure cooker -- but the batch was too big and I ended up taking off the top and just using it as a stockpot.

However, it raised a question: in the MC book there's a reference to bringing the pressure cooker to pressure without bring it to the boil. Is that something that's possible with something like the Presto?

Chris Amirault

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Yes.

Pressure is controlled by temperature: When the liquid inside your pressure cooker is heated it produces steam and being trapped that steam builds your pressure. As your pressure builds the liquid requires higher and higher temperatures to come up to the boil.

Water usually boils at 212F (100C).

At 5 pounds pressure ( psi) it needs to be heated to about 228F (108C) to boil.

At 15 pounds pressure (psi), it needs to reach 250F (121C) in order to boil.

If your stock has too high a liquid to solid ratio it is in danger of venting well before it reaches 15psi so keeping the temperature and therefore the pressure low and below boiling point will work. Reducing the liquid ratio works too, gets you to the magic 15psi for flavor, gives a concentrated stock but not the large volumes this thread is after.With pressure cookers it's not about their price but about their psi generating capacity and most are over-engineered to withstand much more pressure than we can domestically generate.

Edited by TheCulinaryLibrary (log)
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I really wonder about this obsession with not letting the stock boil or vent in a pressure cooker. I don't deny that you could lose volatiles and change the taste if the stock vents (although I can't confirm). But, it seems to me that you are going to lose those components anyway, if you reduce your stock. As far as bringing the pressure cooker to pressure without bringing it to a boil, maybe it is possible with some designs but it seems to me that it would take a very long time and probably some way to monitor the temperature/pressure curves to make sure you don't boil. But if it is at the beginning of the process, you won't have extracted much flavour from the bones so why worry about it? I think the best strategy would be to bring it to pressure as fast as possible and then modulate the heat so you don't vent.

I do think you get a clearer stock and possibly better flavour if you crash cool the PC before opening.

It's almost never bad to feed someone.

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I don't know if it's strictly-speaking true that the liquid in a non-venting pressure cooker doesn't ever boil. It certainly sounds like there is some minor boiling as it comes up to pressure. However, once it is maintaining at pressure, there should be no boiling. For this we refer to Boyle's Law.

--

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Yes

Umm... care to explain a bit more?

As I understand it, it works something like this:

We understand that the boiling point of a liquid is dependent on the ambient pressure. This is why water boils at a lower temperature in Denver than it does in New Orleans -- because the atmospheric pressure is lower in Denver. In understanding this, it is helpful to understand what causes ambient pressure. At simple way to conceptualize atmospheric pressure is to think of it as the combined weight of all the air molecules above us, pushing down on us all the time. Because Denver is so much higher up than New Orleans, there are fewer air molecules above us in Denver than there are in New Orleans and therefore the ambient pressure is lower.

How does this relate to boiling? When we add thermal energy to a liquid, we increase the movement of the molecules in that liquid. This movement can be quantified as "temperature." Eventually, the molecules in the liquid start to move so fast that their movement is stronger than the weight of the molecules in the air pushing down on them (aka the ambient pressure) and they break free of the liquid. This is when the liquid turns into a gas, which is what we call "boiling." So, one way to think of ambient pressure is that it is a kind of "weight" sitting on top of the liquid and holding the molecules down. When we increase the ambient pressure it is like adding a heavier weight on top of the molecules in the liquid. Now they need to be moving even faster (aka be at a higher temperature) in order to break free from the liquid and turn into a gas.

How does this relate to a pressure cooker? A non-venting pressure cooker is a closed system. The first thing we do is put some liquid in there and apply thermal energy. This thermal energy causes the temperature to rise. It also causes the liquid to expand. The expansion of the liquid increases the ambient pressure inside of the pressure cooker. At some point we reach 100C. This would be the boiling point of water at "normal" atmospheric pressure, but ambient pressure inside the pressure cooker is already higher than that due to the expansion of the liquid so there is no boiling. If we continue to add thermal energy to the pressure cooker the temperature and the internal ambient pressure will continue to rise together, but the internal ambient pressure will always have a little head start and the liquid will never boil although it will be very close to the boiling point. In practicality, it seems likely that when we add an abundance of thermal energy to the base of the pan, there is some small amount of localized boiling until the pressure cooker reaches the target temperature/pressure and the heat source has been regulated. At this point, the pressure cooker should equilibrate just below the boiling point for the given internal pressure. This is one reason why a non-venting pressure cooker is preferred. Jiggle-weight pressure cookers at the target temperature periodically vent a little steam in little bursts. Every time that happens, the internal ambient pressure goes down a little bit and there is a tiny bit of boiling before the pressure builds up again and stops the boiling.

--

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Practically speaking Chris, bring it up to temperature so that it starts lightly venting and then dial back just enough so that it no longer vents at all. Then should effectively minimize boiling while maintaining the temperature/pressure that you want.

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"---- in the MC book there's a reference to bringing the pressure cooker to pressure without bring it to the boil. Is that something that's possible with something like the Presto?"

Yes. Get a cheap IR thermometer and measure the temperature of the vessel at full pressure, then just go one degree below that each time you make stock.

"---Unfortunately the conventional stock tasted better. It had a stronger chicken flavor and was better balanced overall.---"

Possibly the Pressure cooker stock has much less evaporation, therefore thinner, less concentrated.

"---When the liquid inside your pressure cooker is heated it produces steam and being trapped that steam builds your pressure.---"

To be exact, Steam is water droplets. Water vapor (humidity in air) is not visible.

"---I don't know if it's strictly-speaking true that the liquid in a non-venting pressure cooker doesn't ever boil. ---"

Not really. In a non-venting PC, heat radiates from the PC to outside air, water condenses inside the coldest spot and gets boiled again. This goes on constantly.

dcarch

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"---Unfortunately the conventional stock tasted better. It had a stronger chicken flavor and was better balanced overall.---"

Possibly the Pressure cooker stock has much less evaporation, therefore thinner, less concentrated.

The CI quote referred to a venting pressure cooker. They did another experiment comparing two venting PCs, a non-venting PC and a conventional stock pot. The result was that the non-venting PC produced the best stock, followed by the conventional stock pot. The stock from the venting PCs was sub-par.

My pressure cooker won, followed by the conventional cooking; both of the school’s pressure cookers scored lower. I feel a lot better.

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As I understand it, it works something like this:

...

This isn't really correct. The boiling point is defined by the pressure of the gaseous water (water vapour) above liquid. It is only very slightly affected by the air pressure and the expansion of the water isn't important for that reason. In an open pot, the vapour pressure is basically defined by the atmospheric pressure. When you heat water to 100 C at sea level it will start to boil - each of those water vapour bubbles in the liquid will expand to the point where the pressure in the bubble reaches one atmosphere (ok plus the pressure of the water above the bubble but that's not significant). The bubble bursts at the surface and the water vapour is carried away or condenses. At a high elevation, the pressure working against the vapour bubbles is less so boiling occurs at a lower temperature. If you put a sealed pressure cooker top over the liquid and you keep the pot at 100 C then the water vapour will be trapped above the liquid water and its pressure (partial pressure of water, to get technical) will build up until it reaches 1 atmosphere, at which point boiling will cease. If you add more heat and increase the water temperature, then more water goes into the vapour increasing the pressure until the two are in equilibrium again. This pressure-temperature boiling curve is a fundamental property of (pure) water - it's different for say ethanol (praise the Lord!).

If you want to increase the temperature in the pot above 100 C, you have to increase the pressure (or add salt or something, but never mind that for this discussion). To keep the pressure cooker from exploding, you have to modulate the pressure and temperature. In a venting pressure cooker, the vent keeps the pressure inside the pressure cooker at or below 15 psi (or whatever set point) above atmospheric. To keep it exactly at 15 psi, you adjust your stove to allow a little steam to release. If I understand non-vented PCs, there is essentially a spring and a marked guide that allows the pressure inside to be a little above or below the target pressure. You adjust the stove to keep the mark at the right level for 15 psi. You can adjust a venting pressure cooker to keep the pressure below the venting pressure but it's not obvious how far below you are. In practice, letting it vent a little keeps the pressure consistent. In either style there are emergency vents to keep the pressure from going too high. But ultimately you have to adjust the heat on the stove to set the pressure/temperature.

So the issue with stock making is that the venting allows some volatile flavour/aroma chemicals to release with the steam. It isn't the boiling per se. Stock is pretty forgiving of how long it cooks so I've been trying to keep my pressure cooker just below venting. If it's a bit too low it might be a bit weak after a given time, but I just work my process to cook for a little longer than might be necessary to account for it. It seems to me there is greater difference in the number of chicken frames or necks I throw into the pot. My strategy is to cook for long enough to extract all the stocky stuff even at a slightly low pressure. In practice my stove is so weird that I get some venting and sometimes the safety vent releases.

It would be really nice to have a temperature probe inside the PC so you just adjust to a consistent temperature rather than a consistent pressure.

It's almost never bad to feed someone.

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I think the problem is that if you bring your PC up to the point where it starts venting, then back off the heat a bit so it stops venting, at that point, you'll be very close to full pressure (and full temp) but won't vent - but you don't know as time goes on what's happening inside - your pressure/temp. could be dropping by the minute, so you'll never really know how much time you had at full pressure.

I have a Kuhn Rikon non venting stockpot. The directions say to bring it to full pressure, then immediately turn down the heat - and if your burner has residual heat, to transfer to a different burner and turn on low. I do the second one because otherwise I get over pressured if I leave on the same burner and turn to low (and it's a gas range which shouldn't have much latent heat, but oh well). But once I transfer burners, I have to keep an eye on it becasue "low" on my range is too low, and over time I can watch the pressure dropping in the spring valve.

My point is - with a spring valve, I can see that my pressure is dropping and adjust accordingly... but with a venting PC, once you're below the vent pressure, you don't know how much lower you are - you could be just below, or way below.

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I don't think it makes a huge difference, to be honest. You could also bring it up to temp, regulate the heat source to the desired "one jiggle every 30-60 seconds" level and then balance a couple of quarters on top of the jiggle weight. This is something like what I do when making stock in my "steampunk R2D2" All-American pressure canner, but I am able to refer to the pressure gauge when I do that.

--

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So... given that I have this venting PC, is it a useful tool relative to a stockpot brought just below a simmer and held there?

IMO Yes. You are making the stock at a higher temperature so it is a lot faster and uses less energy. Even just below a simmer you will be losing volatiles - and doing it over a long period. I think the modern venting PCs like my Fagor vent a lot less than the jiggle-weight ones. With experience you will be able to control the venting pretty well and will figure out how long to cook the stock.

It's almost never bad to feed someone.

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