As a matter of article usage, you can remove the "the". Unless it is referring to a specific sausage (i.e. the one you just ate. That specific one. The one in front of you right now. Name him "John". That is "John the sausage"), the definite article isn't super helpful.
I like the sausage from Hermann more than the sausage from Johnsonville. Because I tried 2 sausages. And this one was better than that one.
But "sausages from Hermann" is a concept. An arbitrary case of sausages particular type, rather than an of a specific instance.
Still, I find this to be an interesting question because the sentence does introduce the following ambiguities:
While we are discussing the specific "Hermann sausages," I want to know a bit more context.
Is it the case that they don't sell other Hermann products? i.e. "They only sell the sausages from Hermann; they stopped selling the mustard from Hermann after Hermann changed the recipe." In this case the article is not necessary, but emphasizes the sausages, as opposed to other things Hermann might provide.
Do they sell other products at all? i.e "They only sell sausages from Hermann; I'm surprised they can make a business on only one product." In this case, the prepositional phrase "from Hermann" adds information about the type of sausage, but the emphasis of the sentence is on the exclusivity of their offered product line.
Do they sell other products, but not other sausages? "They only sell sausages from Hermann; the rest of their products come from Johnsonville. In this instance, the emphasis is placed on the supplier of the sausages.
However, we don't have any more context. All we know is that they only sell sausages from Hermann. (leaving out the "the") This would be correct, although it leaves the ambiguity unresolved. As soon as you went to them, however, you would know that either,
- They sold other products, making it was the case that the only sausage they sold was a sausage from Hermann; or
- If they didn't sell any other product, that it was a Hermann sausage stand.
Leaving in the "the" in the sentence in fact adds the third case where it could be assumed that could they sell other products, and either other sausages, but no other Hermann product, or no other sausages AND no other Hermann product.
Because this is only case that the "the" creates more ambiguity, leave it out unless you did in fact mean that they only sold "the sausages" from Hermann, an none of their other products. Because this adds a level of ambiguity that would have been unnecessary had you just ignored the article, I would likely assume that you intended to add that level of ambiguity, and thus, were intending that specific case.
If I said, "I only drink the tears from my enemies"; you could likely assume that I drank other things. But if it were tears I was drinking, they would be my enemies' tears. What about other things that came from my enemies? Sweat? Blood? No, that's gross.
If I said, "I only drink tears from my enemies", you wouldn't me wrong in calling me a liar if I drank a glass of chocolate milk. However, I might quickly try to clarify that, no, no! I just meant that I don't drink the tears of my friends; didn't that come across? No. I am terribly sorry.
English is full of ambiguities like this. Don't worry about it too much. And pay attention to context.