Grape crusher

The grapes would tend to slip on smooth rollers; it helps to have a serrated (or at least very rough) surface to get a bit of a grip on the grapes to pull them through the crusher rollers.

The roller construction material is not too critical. You want to avoid materials that are:

1) too soft 2) absorb liquids (bacteria grows in them over time if not well-sanitized after each use; wood is a good example of this) 3)degraded by repeated exposure to your sanitizing solution.

304 stainless steel is ideal, electroless nickel plated steel is OK, brass and aluminum are too soft and easily damaged, bare iron and steel are not good because they rust. Avoid coated steel [i.e. galvanized, tin-coated, cadmium plated, chromate-dipped (a golden, often iridescent color)]; these coatings leach into the juice.

Plastics such as nylon, HDPE (high density polyethylene), polyurethane and delrin will also work nicely. You want a durable plastic, one that is not easily damaged if a hard object falls in between the two rollers (like a wayward rock or tool or such).

Natural rubber is not a good choice; many kinds of sanitizers degrade it. Synthetic rubbers such as EPDM, EPR, viton and silicone will work (though EPDM and EPR are slowly degraded by many sanitizers).

For the destemmer cage, I'd use 304 stainless steel. The perforation holes need to have radiused corners, with the convex surface facing the inside of the cage. This is key to minimize cutting/tearing the grapes instead of plucking them off the stems. The optimum hole size and spacing is chosen based on the size of the grapes and density of the cluster... something on the order of 1/2 to 3/4 inch holes on about 2 inch centers is my recollection. I'll need to measure one on Monday to confirm it.

Gene

I think that the destemer may be overly complex to build since, as you say, the hole size is dependant on the berry size and that would mean either a series of graduated holes or several different sized screens.

I had been thinking of stainless tubing rollers but was having second thoughts about the smoothness. I hadn't thought about plastic - nylon and delron is available here in most hardware shops. I'll have to check on prices.

I usually process 150 - 200 lbs of grapes at a time so this thing doesn't need to be a massive device and I'm presently thinking of something that is hand cranked and sits on top of a barrel.

Bruce-in-Bangkok (correct email address for reply)

For your small lot (100-250 pound) crushes, hardwood rollers may be worth a first try; they're easy to make and probably not too expensive to purchase the wood stock. Teak comes to mind as readily available in Thailand. Just make sure you sanitize it well after each use; this would be no different from using a wooden basket press.

Gene

Actually there is nearly no teak left in Thailand. The majority of the teak used here actually originates in either Burma or Cambodia.

I am partial to plastics or metal as in the humid climate here mold is a constant problem.

Bruce-in-Bangkok (correct email address for reply)