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The chocolate forming device featured in this instructable is used to create strings of chocolate without the need for an external or internal heat source.
Now I here yourself thinking is such a thing possible? Well yes it is possible to shape normal milk chocolate without the need for heat. All you do need is a high pressured squeezing system.
Whats more you don't just need to stick to boring profiles like a circle, you can have the filament come out any number of different shapes, but generally the simpler the better.

When the string is first extruded it is malleable and thus workable, you can use it to do whatever your imagination gives you but if you have trouble, I have included a uses page at the end of the instructable. After a while it turns a bit brittle as though tempered which makes it really tasty.
 
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Step 1: Choc Chamber

The chocolate chamber is where all the chocolate is stored and compressed in.
For my chamber I used a Ø60mm aluminium tube with wall thickness 10mm. the length I decided on is 150mm but could be anything from 50mm up.(Couldn't be much shorter because piston is large). I bought this peice of aluminium from ebay seller forward metals (http://www.ebay.co.uk/itm/Aluminium-Tube-60mm-Diam-x-10mm-Wall-x-250mm-Long?item=150337213831&cmd=ViewItem&_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D1%26po%3DLVI%26ps%3D63%26clkid%3D8273219770097453398)
As you can imagine, (not very clear in picture), this is quite a chunky piece of aluminium. It has to be so chunky so that holes can be drilled in the ends to hold the mounts and extrusion plates. Both sets of holes consist of 4 drilled and tapped M6 holes.
drilling these holes straight proved to be quite tricky for me, as the milling machine I had access too was a bit too small with the vise already on it which is why in the photo there are two vises on the bed(the old one is smaller).
Whenever doing low volume tapping operations after drilling on the milling machine, I start the thread off in the machine as to getit straight from the beggining. I think the photos show this operation clearly but do leave a comment if you have trouble understanding it.

Step 2: Piston

This part pushes the chocolate up the chamber, whilst providing a tight seal to stop chocolate traveling back down.through this design, you can also pull the piston back down . Because there is the potential for thousands of newtons (the weight of a few tonnes) to be going through this part, it needs to be robust. This is one reason that I machined the pston from Delrin, a food safe, self lubricating engineering plastic.
I bought this billet from ebay seller dunk247 (http://www.ebay.co.uk/itm/BLACK-ACETAL-BAR-BILLET-51MM-DIAMETER-DELRIN-2-/370595823756?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item56493b808c)

Step 3: Hydraulics

Picture of Hydraulics
The system that I am using to move the chocolate out of the extrusion plate is a hydraulic bottle jack. These pumps are usually used for lifting cars and vans, so there should be plenty of available force to extrude a little chocolate. I opted for a large one (5 tonnes) to decrease the probability of dissapointment as I had little idea with which to choose. A 5 tonne jack was a good choice because the higher the amount of cocoa solids, the more difficult it is to extrude.

Step 4: Mounting

Brief
What the mounting has to do is:
  • Hold the chamber above the jack.
  • Stop the assembly from falling over.
  • Give a rigid surface for jack to press against.
Solution
  • Bolt short bars onto bottom of chamber as close to centre as possible(this will decrease stress in chamber as holes are further apart).
  • bolt these bars to an offcut of kitchen worktop with threaded rod.
  • Worktop is long enough to not tip over when jack is pumped.
  • Flat steel bar is placed underneathe to aid in keeping rigidity and to act as washer for threaded rod. To fit these, slots had to be routed in the worktop bottom.

Step 5: Extrusion Plate

The function of the extrusion plate is to form the chocolate ito the desired shape. The chocolate is forced through a small hole whose shape will become the string's profile.
I started off with a 13mm thick aluminium plate with 2mm and 3mm holes to extrude. Out of these the 3mm hole gave better results. I found that when a large chamfer was put on the in side of the hole.

To make interesting shaped chocolate string you could use any number of cnc machines. eg. laseer cutter, cnc milling machine, 3D printer.
As I only have access to a laser cutter (not a good one), I cut 2x 6mm plates and laminated them together. Due to the brittleness of acrylic I decided to make a cover to reduce the stress acting on plates. Before this cover, all of the plates that I tried cracked before chocolate came through. After, only most cracked. Inspecting the cracked plates, I learned that cracks formed most on sharp internal edges as can be seeen in the pictures. To reduce the likely hood of cracking in the future, corners where the angle<90o will be filleted with radius 0.5mm or more. This will only be a problem with laser cutting and 3D printing as you will always have the cutter radius when milling.
Of the three options for making plates, I beleive that 3D printing could produce the most interesting plates, perhaps building the profile up helically so that the string spirals.

Step 6: Uses

Picture of Uses
P1070457.JPG
P1070458.JPG
Possible uses of the chocolate string:
  • Easy shaping of chocolate over mold.
  • Hollow chocolate egg in egg cup.
  • Decoration.
  • Wound chocolate bar, could have core, eg. thin peanut brittle.
Please leave any other ideas you may have in the comments setion.
AspireBlack3 years ago
Heads up, aluminum should never be used with food unless it has been anodized(electrically oxidized to form a hard outer layer). If not, the Al can be reactive with foods and toxic. machining certainly scraps away any existing oxidation. Always make food tools out of 304 or 316 stainless steel! I hope you read this ASAP. Well written DIY, but remake with stainless!
MR.Geo (author)  AspireBlack3 years ago
A bit sceptical about this comment (what about all those aluminium pots and pans used with heat thus increasing rate of reaction). Please could you post a link to any reputable sources that share this view or maybe a research paper.
Hysteria... While aluminum accumulates in the body over time and can become toxic, there are rules it must follow to do so. After machining, aluminum immediately forms an oxide layer, although not as hard as 'hard' anodizing (there are different types/methods of anodizing that provide various levels of protection). Aluminum is used in antacids, antiperspirants, and..... get this..... ALUMINUM FOIL!
Aluminum is reactive (as is copper, and iron), meaning it will form ions or salts in the presence of acidic or alkaline foods. These forms of aluminum are bad but toxic exposures are usually found in the workplace/industrial settings - not in the kitchen.
Chocolate is only slightly acidic so there may be very small amounts of aluminum absorbed but you are probably in more danger of contracting food poisoning from a dirty stainless steel container than toxic exposure to aluminum from kitchen utensils.
MR.Geo (author)  Old Nubbins3 years ago
Thank you for your input in this matter.
phenoptix3 years ago
Great instructable! I've been wanting to do this since I saw chocolate extruded on a trip to Trinity College Cambridge. I've not seen it since but recently tracked down the papers published by that group.

My only thoughts to improve the instructable would be some nice shots of you bending the extruded chocolate, perhaps a plait?

I see also you're from Beds, whereabouts? I grew up in Dunstable...
MR.Geo (author)  phenoptix3 years ago
I saw that extruder during a science week at school about 4 years ago but had completly forgotten the details except that it had a bottle jack in it somewhere.
Near Shefford
I searched for research materials to do with this but came up empty, could you post a link to where you found the documents please?
These were the guys I saw showing flexible chocolate: http://www.ceb.cam.ac.uk/pages/flexible-chocolate.html

I know a little of Shefford as I used to go to Henlow with cadets.

A paper by them explaining the phenomenon a little is available here
soul_eater3 years ago
Very Nice, i make somethig like that some years ago but i used a pneumatic cilincer and i aded a second cilinder around the one that have the chocolate with a resistance boiling water to help the chocolete to melt a little