Vacuum reduction with a diaphragm vacuum pump

Hi!

I recently purchased a diaphragm (membrane) vacuum pump (<50 mbar, 20 L/min.) to use for (among other things) vacuum reduction as described here: http://modernistcuisine.com/2011/11/vacuum-concentrating-part-2/

I originally chose this style of pump because Modernist Cuisine mentions that membrane-style pumps work well for this, but on reading the instructions that came with the pump, it says "water vapour must me filtered out". Now the instructions also say that the pump is suitable for vacuum desiccation, vacuum distillation and rotary evaporators, so obviously it must be able to handle a certain amount of water vapour (and it is, of course, oil-free), so I am a little confused.

Does anyone have any experience using this type of pump for vacuum reduction? I would imagine at least some of the water vapour would condense as soon as it was exposed to atmospheric pressure. Would this manifest itself as a harmless trickle of water coming out of the pump's outlet, or would this damage the pump? I am a bit nervous of simply giving it a go in case I ruin my new rather expensive pump! :-)

Any guidance would be greatly appreciated!

Thanks!

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Comments

DiggingDogFarm_65362

I would be very careful....most vacuum pumps aren't considered food safe (backflow of potential toxins, etc.)...that's why faucet aspirators, medical vacuum pumps and the like are recommend for food stunts.

richardellard

Here's a link to the precise pump I bought: http://www.ebay.co.uk/itm/261244872676?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

My thinking is that these should be safe. Firstly, the pump contains no working medium which could potentially vaporise and contaminate the food. Also, diaphragm pumps by their nature have shut-off valves which keep the air moving in one direction only, so it's hard to imagine anything going in the direction pump -> food. The instructions for the pump are badly translated, but do contain the phrase "does not produce pollution". Finally, I have seen multiple videos of a similar pump (laboratory 2-stage diaphragm vacuum pump) used at The Fat Duck and one appears in The Fat Duck Cookbook. See pics of Heston with a similar pump:

I'm still not sure how much water vapour they can handle though.

adey73

Richard what else you planning to do with?

You bought a desicator for the thrice cooked chips?

richardellard

@adey73, at this moment in time, I just have the pump. It was kind of a 3am impulse purchase to be honest! :-) But yeah, a desiccator is definitely on my list. Then I can pretend I have a chamber sealer and do desiccation, degassing, maybe aerate some chocolate, vacuum maceration (I really hope 50 mbar is low enough to burst cell vacuoles) etc. Someday I might add a Dimroth condenser to the MC vacuum reduction setup so that I can do vacuum distillation on the "cheap". It seems like with a vacuum pump in one's life, the possibilities are endless! :-) I think my first priority though is to get a vacuum filtration setup. I really want to try some of the fruit juice recipes here on CS, possibly combined with freeze concentration.

I also contacted the seller of my pump to confirm that it's safe for use with food. The example I gave them was vacuuming filtering fruit juices. They confirmed that was ok. I presume they understood I wanted to drink the juice afterwards! They also confirmed that the pump can handle water vapour, although I'm still a bit nervous about sending all the water of a vacuum reduction through it.

@Chris may I ask if you have had any experience sending large quantities of water vapour through this style of pump? The reason I ask you is because you probably recognise the exact pump pictured above from your Fat Duck days.

By the way, sorry for my noobishness, but is something like @Chris correct name dropping when there's a space in the username? If someone writes @Richard somewhere, do I get a notification?

grandpa.yum

put a filter/trap on the intake line. I've seen desiccating filters, metal wools, and micro sieves to remove water vapors before they get to the pump. However, they can be expensive (you'll probably pay close to what you paid for the pump unfortunately) and aren't perfect so you'll still want as little water vapor getting into the line as possible

something like these: http://www.mdcvacuum.com/DisplayContentPage.aspx?cc=3707b105-0d19-4d47-bedd-beab417af429 although I have no idea if this company is any good or reasonably priced, just posting for example

julian.lo

Something to point out—the MC setup uses a vacuum aspirator, which is nice in this case since you can actually flush all of the water vapor from your vacuum reduction through the aspirator (and down the sink if you don't have a recirculating variety) since an aspirator contains no moving parts.

Diaphragm pumps, on the other hand, are not really meant to have huge amounts of liquid flushed through them. Small amounts of vapors passing through the pumps is fine (this happens all the time in the lab I work in), but you wouldn't want to pull a liter of water vapor through it since this would wear out the diaphragm over time. In all of the applications your wrote in your initial post, the majority of the vapor from the system is getting removed prior to entering the pump (e.g., in vacuum desiccation, a desiccant is adsorbing the water vapor and in vacuum distillations/rotary evaporation some sort of cold trap condenses the vapors).

What I'd do in your case is install a trap before the pump, much like what @jon_laur suggested. I wouldn't buy any of the traps in his link though since they aren't meant to handle massive amounts of water vapor. I'd get a cold trap (like this, look around though since Sigma tends to charge a premium) to install before the pump. You'd cool the trap in a bucket of ice water so the water vapor from your vacuum reduction would (hopefully) condense in the cold trap, sparing your diaphragm from getting flooded. Unfortunately, you'd have to empty the water from the trap every now and then.

Good luck with everything and I hope you enjoy your new toy—I'm pretty jealous!

Seth_Ratner_91225

I'm copying this from the old forum to continue the discussion

@adey73 It's in Volume 2, under the "Concentrate!" Chapter, however the use of a vacuum chamber appears in may different chapters, depending on what you are doing with it (concentrating, filtering, de-bubbling, pickling, etc).

@Richard, I left my chamber sealer back in the US, and I've toyed with the idea of getting it out here to run on a transformer. Here's my issue with that plan: Going from 60 Hz to 50 Hz is an minor issue when dealing with AC-DC transformers and heating elements, but with motors, it can be a game of russian roulette. BEWARE THE US BLENDER!! I had a blender (cheap, but functional) work fine until it was put under a difficult load with refried beans, damn thing died in 15 seconds. Since I work with a ton of Americans using US appliances on heavy duty 2000w transformers, I have a decent sample size from which to draw conclusions from. Blenders and Vacuums have high mortality rates on transformers. I've had decent luck contacting companies directly to ask about 50hz of their motors. Great info on the subject here: http://www.eng-tips.com/faqs.cfm?fid=122

For the hot plate, I went analog. I wanted a larger heated surface, and I also wanted to keep the price below $150, in case the transformer devours it on the first use. This model is available all over eBay, though you may have to wait to get one in clean condition: http://www.ebay.com/itm/Sybron-Thermolyne-Nuova-II-SP-18425-Magnetic-Stirrer-Hotplate-/371123873791?pt=LH_DefaultDomain_0&hash=item5668b4e7ff

Alternatively, Maple Scientific makes some "affordable" analog plates that work on European voltage. Not as cheap as US ebay, and I haven't found any reviews, but it's an option. http://www.maplescientific.co.uk/products/stirrers-and-hotplates/microcrystal-top-stirrer-hotplate

As for the aspirator vs diaphragm pump, don't look back! I went with Aspirator partially because I am only in the UK for 4ish years, and I'm fine "settling" for a simple setup until I can buy electronics without transformer worries.

How are you freeze concentrating? One of the first things I want to do with vacuum concentration is to take a clarified orange juice (probably with the agar method) which loses a lot of flavor from clarification, and reduce it down and see if the flavor comes back

richardellard

@Seth, thanks for the blender heads up. And I guess in any event it would be nice to be able to put the blender on the kitchen counter without a 2kW transformer by it's side! Those Dr. Tech blenders are just so darn cheap!

These are the two hotplates I'm torn between:

http://www.ebay.co.uk/itm/321077782189?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://www.ebay.co.uk/itm/281140843218?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Price-wise, they lie in between the used US voltage and new european voltage hotplates you mentioned. I feel like there should be a use for the digital version, which can maintain a certain temperature in a sample whilst stirring it, but I can't quite think of one at the moment. :-) I guess maybe hydrating hydrocolloids, but it seems like a pot and a whisk works just fine for that.

For freeze concentrating, I decided I was going to collect 60% of the sample as (unfrozen) concentrate and discard the other 40% (frozen portion). I freeze the juice long enough so that >60% freezes, then just pass the frozen slush through a sieve into a collecting vessel. I then wait until enough of the frozen portion melts so that I have collected my 60% target. To concentrate orange juice by a factor of 2.3, I had to do this three times. The first two times were fairly efficient: the sugar concentration of the juice was increased by a factor of about 1.4 whilst 18% of the total sugar was lost to the frozen portion. The third concentration was less efficient: concentration by a factor of 1.2 whilst loosing 22%, so if doing it again, I might skip the third concentration.

The choice of 60% was a little arbitrary on my part. I intend to conduct some experiments to see what figure gives the best balance of concentration vs. loss. I also want to see if I can concentrate more if I start with a juice with a lower sugar content. Maybe 25 degrees Brix is nearing the limit of what can be achieved by freeze concentration. (Obviously it's not the sugar I'm trying to concentrate, it's the flavour, but the sugar content is measurable.)

I was wondering: @Seth, have you recorded the vacuum your pump can achieve while circulating room temperature water? Or the boiling point of water under that vacuum? I would be really interested if a satisfactory vacuum reduction can be achieved using an aspirator circulating room temperature water (it would save using tonnes of ice).

Seth_Ratner_91225

I haven't measured the vacuum yet. I'm still getting the whole thing set up, but once I do, I'll see what temps I can get to boil with it.

Be cautious with the size of the hotplates. The 2000 ml Flask is much larger than it looks in MC, and if the plate has a lip on it like your second link, it may not sit right if the plate is smaller than the flask base. I'm probably going to get a 1000 ml flask for smaller jobs after seeing how large the 2000 ml is. The benefit, however, is that the flask is large enough to support a 125 mm buchner funnel for vacuum filtration.

richardellard

Yeah, I remember seeing video of Heston Blumenthal drinking garum out of one of those flasks, so I'm mentally prepared for how big it's going to be! :-) Thanks for pointing out the lip; I hadn't noticed that in the pictures. The flask I'm looking at LOOKS like it would still fit because the base is smaller then the maximum external diameter, but no, analogue it is!

At some point we must compare boiling points! :-)

Seth_Ratner_91225

BLUF: It works! Now give me ideas on what to use this meth lab on!

So I have it set up. Not in a permanent configuration, as the pump I bought didn't come with the tank so I am using a storage container until a more elegant solution is devised. It was able to boil water that was around 65F... I think. I didn't have enough time to run thorough tests, which I will tomorrow. This was with tap water, no ice.

Then I used the hotplate with it to reduce some agar clarified orange juice. Some observations, in no particular order:

- Nothing exploded plugged into a transformer. The pump motor gets a bit warm, but the reduction in speed seems to be within its limits. Either way, I plan to run it with a fan blowing on it.

- The stirring bar has a fair amount of control over the violence of the boil. Too fast and it'll boil up to the vacuum port on the flask. Too slow and you get the large bubbles that can bounce the flask.

- It's slow, My hot plate isn't new or powerful, but the OJ was holding at around 95-100F, and it took over an hour to reduce 500g of OJ down to 160g

- Even with the motor isolated from the pump (as designed by Cole Parmer/Oakton), the water bath gets warm over the course of an hour. I use ice bags (These Ones) by dropping the whole bag into the tank. Once they melt, I throw them bag in the freezer to use again.

- The concentrated OJ has a very unique taste (to me, since I've never done this). I am going to try reducing a batch on the stove to see if the heat has a noticeable effect. I hope it does, since it sorta justifies the whole setup. I may also try it with plain, un-clarified OJ, since clarifying has it's own dramatic effects on flavor.

- Next I'm going to try a bottle of Jack Daniels whiskey.

ttpoker

For those of us who are less informed, can someone please provide a simple parts list so I can attempt to duplicate this myself?

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