the ones that are stainless steel were made of 304.spartanburg steel products in spartanburg s. carolina made a lot of them. apparently,some are made of aluminum--dont know what alloy they are.

 

I don't think there are any of them made from aluminum anymore. I was at AK steel touring their stainless mill and they said that all kegs were stainless now because too many of them ended up in bonfires (after the contents were consumed). It seams the aluminum ones will get hot and blow up, sending shrapnel into all the by standers. The stainless ones can contain the pressure until the valve gives out and relieves the strain. And I I think it was 304 stainless.

 

304 or 316, should be good to go for food production. either are readily welded and such.

 

Man it's been too long since I bought a keg. I've never seen a stainless keg but I don't doubt that they're made of it nowdays.

 

I've used kegs in a similar fashion. Every one I've seen has been stainless. I didn't worry too much about the type since a crawfish boiler isn't under a lot of structural load. I used 309 filler since I already had it on hand. I cut the top out. On the side near the bottom I welded on two half couplers with female threads that match screw-in hot water heater elements, and another coupler for a ball valve drain. Don't forget the drain. You really don't want to be carrying/lifting/pouring 10 gallons or so of boiling hot water. I imagine hot maple syrup would be worse. You can't shake it off.

This is similar to what I used. http://www.mcmaster.com/#4464k226