If so what kind are OK to eat? If no, why not? Sausages are a "processed" food since I'm pretty sure that you carve one out of an animal. Is it the meat content that is important, or does the packaging play a role as well?
The only right answer is: Check the ingredients.
What is a processed food? If it includes non paleo ingredients, I'd say it was processed. Most sausages include filler proteins (soy or not specified), filler starch (usually grain, but can be potato starch), which may or may not be hydrolyzed, colour, flavour enhancers (MSG and/or sugar or sweeteners) et cetera. The casing may be natural, it may be made out of collagen or it may be plastic. The ingredient list probably won't even tell you.
I'm not sure you'd ever find non-processed sausages according to this definition except at speciality stores, or at your local charcuterie.
Some butchers specialize in their own fresh sausages. They'll be happy that you're interested and will tell you all about their products. I get a really good mild Italian that is rough ground great quality pork plus seasonings - that's all. It's great for breakfast or in sauces. I bet you have someone close to you that will make some up for you if you ask.
Unfortunately you really just need to look at the details of the ingredient list. I've looked through tonnes of sausages in the UK because my partner really likes them and better that than no meat at all and they all contain a wide variety of different combinations of bad things. All of the cheaper ones and most of the premium ones are awful, just psuedo-meat really (mostly breadcrumbs).
The half decent ones I found* were around 95% pork and most of the rest breadcrumbs. The best I've found were a bit carbier, but the carb was potato rather than grains, so less gluten. Other than than there's very little unpaleo about sausages per se. The casings can be just be from animals themselves, in which case no problem. Other than that the things to look out for are masses of salt and the worse sorts of additives (nitrites etc).
Continental dried sausages also tend to be very good, though the commercial ones can have a surprising amount of dextrose in them. The main thing to worry about is the salt. That said when I went trail-walking for two weeks, having dried spanish sausage was a lifesaver.
*Sainsbury's Taste the Difference range, for any Brits reading. The outdoor reared ones are the meatiest and the pork and herb are the ones with potato rather than wheat, for some reason.
Cheap price/Low quality sausages = Bad
Good quality/High price sausages = Good
Check the ingredients. If its a mile long give it a skip, if it's short and mostly good stuff then they are good to go.
I think 9 times out of 10 a whole steak/ribs/shank etc would be a 'healthier' choice, but personally I am not a purist and since I am quite young sausages represent an economical food I can eat and cook very quickly. And 99/100 this is going to be a better option than eating out.
Here are some good instructions, from Barry Groves, on how to make sausage meat, with ground meat, not the kind in casings. There are also instructions for curing bacon.
"I call it sausage meat, but, as I don't use sausage skins it is probably more accurate to call this a burger mixture.
Buy minced pork or beef meat and ask the butcher to make it up into 500g bags. Freeze all but that which you want immediately.
In a bowl, put 500g of minced meat and open up with a fork.
Sprinkle with a little dried mixed herbs and salt to taste, and mix.
Do this several times until you have sufficient herbs and salt and these are well mixed with the meat.
This amount will make about 6-8 good sized burgers. We use them with eggs for breakfast. Try also curry powder, garlic powder, turmeric, cumin, Worcestershire sauce, etc., for other flavours.
To cook, heat fat in a frying pan, cut out a lump about the size of a large egg, place in the frying pan and spread to a flat about 12mm (1/2 inch) thick.... Fry for about 4 minutes each side.
The rest, if...used within three days, can be kept in a sealed bowl in the fridge."
http://surefoodsliving.com/2009/05/hot-dogs-and-sausages-gluten-free-and-dairy-free-list/ is a pretty good meta-list... with hyper-links for each type. BUT, that is a list of v. large companies and corporations.
See Below for going a bit more local.
Also, search out your
local Bavarian / German eatery, look for a website (or call them on the phone), and find out who makes their FRESH sausages...
It is usually themselves, or a local butcher.
My example: http://www.liehsandsteigerwald.com/ is in both Clay, NY and Syracuse, NY and one of their pledges is "There are NO fillers, additives, or cereals in any of our Homemade products."
HEY! NO CEREAL! YAY!
After you've dodged the
Evil Gluten Bullet, then you can get into smaller details like grass-fed proportion of meat and what other ingredients there are Within.
remove the meat from the casing and you should be good to go. unless the meat is mixed up with that bad crowd of nitrites/nitrates (but Wolf says this isn't something to stress in one of his podcasts)... and then it's your call.
I was surprised when I saw some of the ingredients in pre-packaged sausage in the supermarket. I opt for the "Jones All Natural" variety from the freezer when I get the urge since they're at least free of nitrates and preservatives.
I avoid sausages that contain gluten. Aside from sausages that traditionally contain a small amount of dextrose (salami, for instance), I avoid ones with sugar (I'm thinking of "maple" breakfast sausages, things like that) as well.
Sausage casings are made from a layer of animal intestines or from collagen taken from pork or beef sources. While the latter counts as "processing", it's old and probably harmless technology. I know of no reason not to eat them.
I am currently inclined to the view that nitrates/nitrites aren't a big deal, but I know some people seem to be sensitive to them. If that's you, best to avoid 'em.