This is my first attempt at a DIY home vacuum chamber for sous vide and marinating food in the kitchen. I spent about $170 including the cost of a new vacuum pump. Here's a demonstration:
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Before you start out, there are two things you need to keep in mind:
- If you use a good vacuum pump you are dealing with very high pressure. Atmospheric pressure is over 14 psi which doesn't sound like much until you realize that 1-foot cube has just over a ton of pressure on each side. I crushed a thick metal pan (see picture) that I thought could handle the pressure.
- Keep your fingers away from the air-intake of your vacuum pump. It will tear or rip off your skin in no time. You are a complete moron if you check to see that your vacuum is working by using your fingers to feel for air. Do not ask me how I know this.
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I have a commercial vacuum sealer and i have some experience, regarding some questions that are in the room.
There are two controls. One is for the vacuum, the other for the time of the sealing heater.
Depending on what you pack, you have to adjust the vacuum.
If you have free liquid, you can't set it too high, otherwise it starts to boil. There are no tricks, to circumvent this, it's physics.
http://en.wikipedia.org/wiki/Vapor_pressure
The pressure on the outside is reciprocal to the vacuum. (1000g per square centimeter at a theoretical total vacuum 0 hPa)
Since you never reach a total vacuum, it will be less than 1000g. But then, at 10 hPa or mBar, you still have 990g.
That is close to a metric ton on a square foot... even if you are far away from a "total" vacuum. (compared to vacuums, used in thin film deposition or semiconductor production, which is around what you have in space)
To reach such vacuums, you need massive diameters in the "pump tubing"(actually stainless steel pipes with a diameter of 2-3 feet), otherwise the molecules don't find the way into the pump. (molecular flow) Funny behaviour..
Because of gassing out, you are very limited in the materials used. Stainless steel, teflon and even gold as gaskets...
And yes, i worked on such equipment.
http://en.wikipedia.org/wiki/Vacuum
The sealer should be a flat heater type, not just a wire.
It should be 2-3mm wide and covered with a teflon tape. (The brown tape in the picture.)
This way, it even securely seals, if there is liquid inside the bag.
One commenter suggested, that it would help to have some sort of mesh in the bag. This isn't needed, for these types of vacuum sealers.
For the cheap "vacuum" sealers, with the bag at atmospheric pressure, during the seal, you definitely need a meshed bag.
But then, most of these sealers are only toys.
Pictures of the sealer and sealed selfmade "Weisswursts".
The pan I'm using in the video is aluminum. Do you see any problems with out-gassing using aluminum?
I'm not familiar with inHg, but from what i looked up, 29.5 inHg has to be "total vacuum"? Then 27 is less, right?
Although, 29.5 is atmospheric pressure an 0 is vacuum most of the time
On some old vacuum meters, we had Torr as unit, which is mmHg and 760 mm equals atmospheric pressure at sea level, 0mm is "total vacuum".
With my vacuum sealer, i set the vacuum by trial and error. Depending on the goods to seal.
When i put a cup of water inside, the pump won't stop, if i set the vacuum too high. (The water boils)
The out-gassing of aluminum isn't a problem at these pressures.
The top cover of my vacuum sealer is cast aluminum as well.
This is only a problem at high to ultra-high vacuum, where you essentially have to count molecules, to measure the pressure.
Isn't the idea to replace the air with water vapour, and then when you re-establish the pressure, the water vapour recondenses, and you have removed the air?
I would think that adding a small amount of hot water in a little cup or something beside the food or even in the bag is actually desirable.
Water vapour has a huge volume, in comparision to liquid water.
This volume needs to to be pumped by the vacuum pump.(your pump won't be big enough, except you whipp up some serious cash...)
If this happens for example on our Weisswursts, their skins rip.
At least not in food packaging. The idea behind vacuum sealing is to remove as much air from the packaging as possible.
If you want to keep the food from oxydising, you need to remove as much air as possible from the package.
On the long run, this only helps, if you use bags with a oxybarrier. (Those bags mostly have a metallic appearance.) Standard PE bags won't do, polyethylene is oxygenpermeable.
Food preserving in combination with vacuum sealing also requires immaculately clean procedures.
Vacuum sealing alone won't do. You will need a preserving technique, like pasteurizing, brining with salt, or adding food grade preservatives like sorbate and so on(not my choice).
For example: the Weisswursts on the picture have been vacuum sealed hot(pastuerizing temp) and cooled in a ice bath in the bags.
The smoked salmon has been brined with salt and smoked. Brining removes free water from the salmon and adds salt.
Together with the smoking and cold storage, the salmon keeps at least for 8 weeks at temperatures above freezing.
By the way, brining fish and meat in a vacuum bag is a really elegant way for small batches.
For dry goods like herbs or teas, you don't want any moisture inside. You can set your vacuum higher here.
I think i get your point, but i really don't see a positive effect.
They have cheaper ones; look in the "Customers Who viewed this item..." section.
I've spent a lot of time with vacuum pumps and they have spoiled a many samples. The biggest problem is that every now and then they BUURP and spit out lubricant just when you turn them off or release the vacuum. In light of this, I wouldn't hesitate to get two stopcocks: Close off the one closest the pump first, then the one closest your sample, let air into sample chamber, turn off pump, slowly let air into pump.
People have been eating charred meat for a long time - meat with exotic lubricants or outgassed chemicals from the tubing? not so long.
A cold trap and filter is also a good idea as most pumps can become contaminated by the fluids evaporated by pulling a vacuum.
Try sealing all the threaded connections with epoxy instead of teflon.
Do you think you could freeze-dry some food?
If you freeze something say, apple slices. then put them in the vacuum until all the moisture sublimates and is evacuated. Would this be like astronaut food?
If you insist on re-using bags do not just use dish soap and hot water - after washing them very well (disposing of any that feel greasy in anyway) spray the interior with a 10% bleach solution and allow to air dry. Boiling them won't work as they'll deform at 195F. Either way, I wouldn't re-use them for sous vide.
Note: I've been a restaurant cook, I do home canning and preservation, my partner owns a couple restaurants, and I've read the county health department training manual for food handlers and managers for fun. While that's not a huge amount of credibility that's what I'm working from with this comment.
Now, something to keep in mind is that reusing the bags isn't necessarily an ecological win either. You are using a not inconsiderable amount of water, electricity, detergent, and generating waste water in cleaning them. Being that zip lock bags *are* recyclable I'd go that route in order to reduce your waste stream. By reusing them you do save some money - but it's less than 7 to 12 cents per bag (assuming you buy in bulk). So you really have to balance that against the possibility of getting someone sick.
Like I said, the closing mechanism is really ingenious *and* I think the process you are using is pretty cool. The only thing I would caution against is trying to reuse the bags. I really think that's a false economy when you factor in the increased chances of food borne illness. Restaurants run on a really tight budget my feeling is that if they felt they could reuse bags in order to save money they would - but you really don't see them doing that. Obviously, you should do what you think is best in this regard but I hope my comments have given you something to think about.
Second, with regard to the trouble you're experiencing with wet foods, me hunch is that you're just not pulling a strong enough vacuum. I use a VacMaster at home and, although the chamber size is much larger than the bowl you're using, it runs for quite a while before sealing. It pulls ~30" of Hg (should be the very end point on your pressure gauge) and it pulls it for maybe 40 seconds before sealing.
As the pressure in the chamber drops, water will start to boil. As it expands to steam (which is about 1600x the volume of liquid water) it has the effect of increasing the pressure in the chamber. To combat that, just let the pump run for a while more before sealing. You're also on the right track - sealing cold foods and liquids works better.
Anyhow, great job!
For example, can you determine the length of time between when the bag is sealed and the vacuum is released? Is it (relatively) instantaneous? Is the sealer doing anything in addition to evacuating the chamber and sealing?
I will also explore creating a better vacuum. I was told (apparently erroneously) that commercial chambers only get to 27-28" Hg so I figured that 29" was good enough. I think that the leaks are in the hose connections; if I shut the ball valve and turn off the pump it takes more than 5 minutes for the chamber to lose its vacuum (which I thought to be surprisingly good) but the hose seems to lose the vacuum quickly.
I will try some different tests and posts the results here. Thanks again and keep the comments coming!
With a better seal you may create a better vacuum and will be more likely to remove any fluid from the bag.
And with your setup there looks to be only 4 leak points so it should be easy enough to ascertain where it is leaking and fix it.
Stopping the leak will improve the vacuum, but you may not notice the difference.
If you close the valve after getting the vaccum and don´t have leaks, then the needle could stay fixed indefinitely. If see the needle moving fast, then you have leaks.
The vaccum you get also depends on your place´s altitude. At sea level you can get more than at high altitude.
Now comes the hard part : good cooking !!!…
:-D