The How and Why?
One might ask, how were so many patents granted for coffee roasters? In the language of the statute, any person who "invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent," subject to the conditions and requirements of the law. Even if the subject matter sought to be patented is not exactly shown by the prior art, and involves one or more differences over the most nearly similar thing already known, a patent may still be refused if the differences would be obvious. The subject matter sought to be patented must be sufficiently different from what has been used or described before that it may be said to be nonobvious to a person having ordinary skill in the area of technology related to the invention. For example, the substitution of one material for another, or changes in size, are ordinarily not patentable.
The key wording here is, "new and useful improvement thereof." As you browse the patents listed on this site, you will be amazed by what the inventors are claiming as new and useful. The heart of the patent is in the claim set, listed at the end of each patent. These claims are what the patent office grants to the inventor for protection of their invention. Although many pages are written explaining the invention it all boils down to the claims.
If these old coffee roasters were being patented today, I dont think they would slide through the patent office as readily as many of them did in the 19th Century. I think patent examiners were a little lax when reviewing the requirement, "obvious to those skilled in the art."
For further information on U.S. patents, go to the USPTO, http://www.uspto.gov/web/menu/pats.html where you will find a wealth of information on the patent process.