Cooking under vacuum - Gastrovac

[Sparren]

Hi, I'm a bit curious about the technique of cooking in vaccum. Does anyone have any experience with the Gastrovac?

First of, deep frying (tempura) in 80c, will the batter really become crisp and have the taste and color as with regular deep frying?

 

I have also read that when cooking in Gastrovac there's no loss of liquid. This sounds a bitt strange to me as I suppose the vaccuum pump would suck out both air and steam.

Reduction at low temperatures would be one thing I would like to achieve.

 

Thanks!

[pbear]

I've never used one, but there was a bit of discussion in the original sous vide thread.  See here.  The short answer to your questions seems to be crisp yes, color no.  BTW, vacuum reduction is discussed a few posts later on the same page.

[Mjx]

You'll find a lot of discussion of cooking under vacuum in the forums, just look for the discussions of cooking 'sous vide' (for whatever reason, the French term for 'under vacuum' caught on early). There isn't much that is specific to the Gastrovac, apart from this, in the Sous Vide: Recipes, Techniques & Equipment (Part 1) topic, but I'm fairly certain that the information on various other vacuum chambers is applicable.

[pbear]

Actually, cooking sous vide is not cooking under vacuum.  It's a common misunderstanding, but that's precisely the point Nathan was making in the linked thread.  Rather, "sous vide" is shorthand for packed under vacuum and cooked at low temperature, usually until pasteurized, but the cooking happens at standard pressure.  Notably, one can get many of the advantages of this process without vacuum packaging, e.g., by using zip-top bags.  What one loses is extended storage times, which was one of the main original purposes of the process.

 

By contrast, the Gastrovac cooks under partial vacuum, which reduces the temperature at which water changes phase (to steam).  This enables one (for the low, low price of almost six thousand bucks) to fry at low temp and to reduce liquids with less impact on flavor molecules.  One can do neither of these things with sous vide.  Indeed, I prefer to call the latter low temp in part to avoid this confusion.

[Mjx]

I'm not sure if we're looking at the same Nathan Myhrvold post, but in the one I was referencing, he states that the Gastrovac is 'just a vacuum chamber'. It sounds like since then, the Gastrovac has been redesigned into something rather different (and actually, sous vide is, literally 'under vacuum' (not necessarily a complete vacuum, since that's not so easy to reach/hold in most kitchens), so the intent of the term is going to depend on the context (e.g. cooking sous vide, infusing sous vide)).

[pbear]

Back to the OP.  Do you have a Gastrovac?  Access to one?  Just curious?

[Sparren]

I agree that the term Sous Vide is misleading. To me what is called Sous Vide is cooking at target temperature, usually vacuum packed in water bath.

I'm considering investing in a Gastrovac but to justify the cost I need to know what I can achieve with it and also have an idea of how "magic" the results are. There seems to be very little information on the Gastrovac except for some reviews.

So far my conclusions are:

 

• It can cook (boil) food at low temperatures in oxygen free environment which mean colours, taste and nutrition's are better preserved.
• You can infuse food with liquid during cooking
• You can deep fry at low temperature (80c) and batter will become crisp but not change colour and there will be no maillard reaction.
• I'm still not sure you can reduce liquid with it but I guess you can if the pump is on all the time. It has a hose for evacuation, but I'm not sure it's suitable for this.

 

I can infuse cold food with good results in my chamber vac, but infusing hot food drags moisture into the pump which is may damage it.

 

I think I will pass on the Gastrovac for now. At least until I have had a demo of it or talked to someone who is using one. I just placed an order on a Ultrasonic device, so I will probably have something fun to play with next week.

[pbear]

Have you seen the manual.  Seems to me it answers some (but not all) of your questions.

[Sparren]

Have you seen the manual.  Seems to me it answers some (but not all) of your questions.

 Yes I have had a look at it and technically it looks like it would be possible to reduce with it (at least for 99 minutes, then pressure has to be released and rebuild) but since I never heard of anyone using it for low temp reduction I have my doubts that it may not be suitable for the purpose. I have emailed the manufacturer but so far no answer.

[pbear]

Gotcha.  Good luck in your research.

[dcarch]

--------------------- but since I never heard of anyone using it for low temp reduction I have my doubts that it may not be suitable for the purpose. ---------------------

 

Freeze drying food uses low pressure reduction.

 

dcarch

[paulraphael]

I'm curious about this thing. It's hard to imagine the advantages of low-temperature frying (it seems the point of frying is the high temperatures that it allows).

 

But low temperature reduction offers worlds of possibilities.

 

The Rotovap is probably the most powerful tool for the job, allowing precise control over temperature and pressure, and capturing the distillate you can make all kinds of things that are impossible with conventional tools (and some of the most amazing tasting spirits ever, if you don't tell anyone about it). Unfortunately these gizmos are awkward, complex, and generally cost even more than a gastrovac. They're designed more for a lab environment than a production environment. 

 

On the topic of sous-vide terminology, yes, it's misleading and annoying. I blogged about it in the intro to my sous-vide series.

[Sparren]

I have the rotavap on my wishlist aswell. However with vaccumpump and chiller its three times more expensive as the Gastrovac and as you say it seems awkward and very complex.
It would be fun to play with though.
Good article by the way.

Edited September 2, 2015 by Sparren (log)

[paulraphael]

I'm still not sure I understand the gastrovac. It looks like a serious professional piece of kit; I just don't understand the low-temperature frying aspec. I understand using it for rapid infusions or for no-cook reductions, but frying thing needs better explanation.

[AlaMoi]

not actually a whole lot to wonder about.
couple of technical points:

when H2O changes from a liquid to a gas the volume increases by roughly 600x.  under vacuum, moreso....
so a teaspoon/5ml of liquid water will become 3 liters / 3.17 quarts of water vapor.  the question about 'keeping the vacuum pump running' - ? - yeah, you're gonna need that.  and you're gonna need a well designed filtering system to keep the misc. bits & stuff from the pot from entering the vacuum pump and causing failure$.

low temperature deep frying - when food gets plunked into the deep fryer there's all this bubbling activity.  that is water/moisture in the good turning to steam and blowing out of the foodchunk (600+ to 1, see above....)

since in a vacuum liquid water turns to water vapor at a lower temperature, the theory is one can use a lower temperature for the oil - or put into marketing BS:  low temperature deep frying.

(actually, some benefit there - lower temp oil = longer oil life, fewer murderous free radicals, etc....)

now, the theory is nice - but if you have four ounces of chicken you want cooked / deep fried, it takes a certain amount of heat energy absorbed from the hot oil into the chicken.  the absence / removal of water is not what cooks the chicken, it is the exposure of the chicken flesh to heat that cooks the chicken.  it takes more heat energy to turn liquid water to water vapor, than simply to heat up the water/chicken - the old high school science class "heat of vaporization" thing.  the lower the temperature, the slower than goes, and one could speculate, the drier out the chicken becomes.

in the end it's a balancing act - high heat cooks fast, lower heat cooks slower. 
does it work better/worse than "conventional __________" - no clue.

[paulraphael]

I don't find that clear at all. You can cook food in oil at any temperature. At what point it stops being oil-poached and starts being deep-fried seems ambiguous. 

 

Lowering the pressure has the effects of lowering the boiling point of the oil (which would seem unimportant) and lowering the boiling point of water (as you've said). This latter effect seems central to what vacuum frying is about, but why? Why should we care about the boiling point point of the water?

 

According to Myhrvold and company, water boiling from the surface during deep frying contributes to agitation of the oil and improved heat transfer, and at the same time keeps the surface temperature at or below the boiling point of water—briefly. Once the surface dehydrates and gets crisp, the temperature rises rapidly and the surface browns.

 

So why do we care so much about the brief period when water's boiling from the surface?

 

There's clearly something going on here ... vacuum frying has become a real thing in the snackfood industry. But the mechanism is not obvious. Reading the manufacturer's info has not clarified anything, nor has reading the two research papers I've found on the topic.

 

This particular study says, in regards to vacuum-fried foods absorbing less oil, that

 

"Scant information is available on this topic because scientists are only just beginning to perform research in this field. However, it is clear that vacuum frying of non-traditional fruits and vegetables has great potential."

Edited September 13, 2015 by paulraphael (log)

[AlaMoi]

the original point is about frying, specifically deep frying, in oil - so the poaching thing is an aside.

the boiling point of cooking oils is quite a bit higher than the smoke point - the oil temps used in plain old deep frying at the corner deli do not approach the boiling point of oils.  I'm not sure how decreasing the boiling point of the oil would do anything in this situation.

the article cited talks about carrot crips - and reading through the article:
- the differential temperature oil to water boiling point is maintained.  so if we assume a 'normal' fry temp of 350'F vs. 212'F for water, that's 138F' difference
- as pointed out in the article, reducing the boiling point of water and likewise the oil temperatures means the vitamins, etc. are not heated to the same temp = less reduction of 'health benefits' and secondarily since the oil is not heated to such a high temp it does not oxidize and create toxic (their description) compounds in the oils.

this all makes sense in context of (most) chemical reactions (assuming the detrimental, in this case) happen faster at higher temperatures.

the paper gives the methodogy - for vacuum frying they used a pressure of  1.9 inches of Hg, or 0.93 psi (this is a near total vacuum....questions of practicality in reality exist...) which means the water boiling point is in the neighborhood of 100'F - about half the normal 212'F - not far off hot tap water in the kitchen - and an oil temp of about 240'F.  

and cooking times in the 2-4 minute range.

the bottom line to this:  these folks are talking some real serious deviation from the usual, ande it is an interest experiment, but results/conclusions may not apply across the board.

it also raises a question of what to do about pathogens that may be in/on the food surfaces - those temperatures are too low to be effective against the common 'food poisoning' bacteria.  leaving the food in the oil long enough for the 240'F oil temperature to penetrate the food mass will most definitely produce something crisp!

although I'm a fan of 'low&slow' cooking for meats, 100'F steam is quite outside a usable temp - and 240'F will not brown any breading, etc. 

 

my take-away: is it might work for creating a carrot crisp - but those conditions/etc are not likely to produce satisfactory results with fried chicken, fish, etc.

[paulraphael]

The point about poaching is that I'm not aware of a hard delineation between poaching and frying. Possibly it's considered frying if done anywhere above the boiling point of water, but I'm not convinced of that. There's likely a pretty big no-man's land in between.

 

And yes, I understand the benefits of frying at a lower temperature w/r/t development of toxins, but not w/r/t the other stated cooking benefits, including oil absorption. It does seem to be related to the boiling point of the water relative to the oil temperature, BUT—your descriptions don't explain the mechanisms, the scientific articles don't explain the mechanisms, and one of the articles comes out and says the scientists don't understand it either.

 

So my broader point stands—I don't understand vacuum frying. The only thing I've learned over the last few days is that no one else seems to understand it either.

[AlaMoi]

....So my broader point stands—I don't understand vacuum frying.

 

that would make more than one of us.

 

you are quite correct as to the maker's literature, etc.  all fluff, no facts, no basis, no explanations.

 

reducing the boiling point of oil is idiotic.  no cook anywhere uses cooking oils at or near their boiling point.

things "cook" by the absorption of heat, not by the evacuation of water.

 

were that true, you could cook your meats in the freezer.  at well below water freezing points H20 sublimes from solid form (ice) to gaseous form (water vapor) without becoming a liquid (aka "water")  in the home, it's called freezer burn; when done in controlled fashion, it's called "freeze drying"

 

as to oil absorption, the entire experiment involves 20 gram (0.705 ounces by weight) batches of carrot sticks.  the authors do not claim this is a magic bullet to greaseless fried chicken. 

 

why do I have the idea tempura batter deep fried at 240'F might absorb more oil than when deep fried at 375'F?

 

it is an interesting theory; cooking masses of chips in a near perfect vacuum is a big time serious physical/engineering problem.

the underlying issues probably explains why so few high end kitchens are now equipped with their own liquid nitrogen generation plant - it may be "doable" - just not practical.

[dcarch]

When you deep fry, you need to turn the food upside down once in a while so that both side can be fried evenly.

 

How do you do that in a vacuum fryer?

 

dcarch 

[AlaMoi]

When you deep fry, you need to turn the food upside down once in a while so that both side can be fried evenly.

 

How do you do that in a vacuum fryer?

 

dcarch 

 

don't mention that to KFC.  it'll ruin their whole day.  after all, pressure frying is just the absence of a vacuum......

[Sparren]

About reduction I finally got my answer:

Dear Mats,

 

I’m sorry for my late answer. This equipment is not a good option for this purpose. I advise to use an evaporation unit from the same brand ICC . I have attached the instruction manual in order to have a look on it.

 

If you are interested please contact to the owners of the brand International Cooking Concepts (ICC). Inma Ramo (inma@cookingconcepts.com) in order to know how to place an order.

 

Best regards

 

Jordi Gómez