Extruding Chocolate & Other foods

Hi there,

I've been making various models to extrude chocolate reliably, with tempering ;-) , and this relatively simple design seems to work best, i wonder about food safety, and help / recommendations / part providers (europe if possible) are most welcome.
Also i'm planning to reuse this same setup with other foods, like sugar (melt), royal sugar (eggwhite), and maybe but not sure pastes that may contain some fruit content (acid)

I'm using a 5mm tivoly wood drill bit (single spiral grove) of 100mm long
It's inserted into a 6mm tube (my first attempt was with an alu tube, but will switch to PP tubes)
The tube has a notch at the root of the drill bit so it sucks in molten chocolate
Melting is done with nichrome wires wrapped at various spots and embedded with silicone rubber for electric protection
Cooling is done either by blowing air (convective), either by exposing to a cold surface (radiative)
The nozzle is made of silicone, with nichrome wires embedded

My concerns are regarding food safety, and i'd love your insights

Extrusion screw
- the drill bit, is probably made of high speed steel, but i dont know if it can be considered as being food safe (been reading this [www.bssa.org.uk])
- can 316 steel drill bits, or archimede screw be found ? or machined ? or scavenged from food spare parts ? been looking all around, no success so far

Tube & friction
- the drill bit turns at something like 30-60 rpm, some friction occurs. Chocolate being fatty, it helps as a lubricant
- the tube can be made of 304 steel (found these with misumi), but i wonder about metal on metal friction and food contamination (at 100mm long the 5mm drill bit is gonna bump on the sides)
- the tube can also be made of igus tribo food safe plastic (the sell 10mm rods i can drill to make it a tube), some of which are rated up to 180°C; same problem, friction = contamination to some extent

Hard on Soft, Soft on hard
- considering that the chocolate is fat, it helps (a lot) lubricating the thing. So it's a relatively low stress situation, and i wonder if making the screw with nylon or ptfe (soft, easy to machine), and leaving the tube in inox be a better idea
- temperatures are for chocolate a quick (2 minutes) priming / start at 50°C then drops to 31°C
- and for sugar (actually it's isomalt), at 150°C

Cooling
- So far, i'm using a PC cooling fan. But maybe it's a bad idea, if there's something better i'd love to know
- thought of using copper pipings that flows 2-4°C water so that is presents a cold surface all around the nozzle. Not sure it will work, so leaving that as a last resort.

Nozzle
- There are food safe silicones, i'm not a specialist, would like to know more. Is it the platinum cured silicones that are food safe ? Some putty pastes claim it is food safe (Pebeo / Gedeo), or i could use the ones the dentists use.
- Electric conductivity, i'm getting confused on this one, searches show both dielectric and conductive silicones. Because i'm embedding nichrome wires, i'd like to know.

Cheers !

Ramez

Check out the "compliation" of food safety standards for sanitary construction of food equipment that the University of Florida's Food Science and Human Nutrition Department put together.

http://edis.ifas.ufl.edu/fs119

Basically Stainless Steel of a particular grade and non-toxic, non porous materials for everything.

Very helpfull ! thanks!

I have abandoned the use of a screw in contact with food. Made a lot of tests, and there is always some grinding that happens and residues go in the food. Not comfortable of choosing which residue is acceptable ... so i switched to a peristaltic pump design, with silicone tubing, it's far less easy to setup (especially for controlling the temperature), but i guess, it's safer.

Also you need to use Silicone free sealants in food work.
And if you are going to sell then you must use silicone free food save lubes on ALL parts.

Experimenting with this has long been on my to-do list, but I've been thinking about a different route. Instead of trying to create the body of an extruder, I'm going to try using a large, food-safe syringe for the chocolate. I use an aluminum print bed, so my plan is to print the chocolate onto a silicone baking mat. If cooling's an issue, I'll put some ice around the print area, or even under the mat in a tray. My thought for the extruder right now is to have an arm of some sort moved up and down by lead screw. That'll fit into the plunger of the syringe to give me the ability to extrude and retract. I'm thinking of using some low-ohm, high-wattage resistors to keep the chocolate at temperature. I'd considered nichrome wire, but I suspect the resistors will provide an easier-to-manage heat source, and perhaps a more diffuse one. I'll still melt the chocolate on the stove, though, and I'll obviously be limited by the size of the syringe. I'm never going to run a production line with this, though, so those aren't important concerns. The main thing is that I'm not printing, machining, or doing anything at all to the parts that will actually be in contact with the food.

I've long thought about a sealed small stainless steel or copper tank with rounded edges and a heating element either attached beneath or just under. Something to get it up to the right temperature to temper. I'd have an inlet on the top to which I'd attach a pump of some type via tubing to pump air IN to pressurize the tank enough that the chocolate would come out of the outlet tube. The outlet would be another tube which would either just be insulated or have a heater around it and run to the nozzle.

Of course It'd have to be food safe, no sharp corners for stuff to get gunked up in, proper inlets and outlets. I'm assuming no solder if copper. Food safe tubes and stainless steel nozzle. The tank would have to be thermally insulated from the rest of the machine, probably by teflon mounts.

Edited 1 time(s). Last edit at 07/21/2016 07:19PM by FA-MAS.