baker's yeast (with no articles)

Would someone explain why they use "baker's yeast" without any articles in the following sentnce?

But little was known about how autophagy happens, what genes were involved, or its role in disease and normal development until Dr. Ohsumi began studying the process in baker's yeast.
excerpted from: Yoshinori Ohsumi of Japan Wins Nobel Prize for Study of 'Self-Eating' Cells - The New York Times

Can't you use "a baker's yeast" or "bakers' yeast"?

Can you also say "butcher's meat" like "We don't buy butcher's meat"?

Thanks in advance.

Hirashin

You don't need particles with baker's yeast or butcher's meat.

I think this is because of the uncountable nature of both yeast and meat. You would use a particle if you described them in terms of units of measure, like:
an ounce of baker's yeast
a pound of butcher's meat
Without those units, particles become unnecessary.

Thank you for the help, Majestic. I didn't know that. Articles are always puzzling me.

Actually, the principal reason an article is not used in this case is because the noun is being used in the generic sense. You would also not use an article with a countable noun in this same context.
Example:
Dr. Ohsumi began studying the process in dogs.
Even though "dog" is a countable noun, it is used here in the generic sense, referring to dogs in general, rather than any specific dog or dogs, and so an article is not used. Although using "the dogs" or "some dogs" in this sentence would be grammatical (albeit slightly awkward), either of these would somewhat change the sentence meaning.
Here is one more similar example to help drive home this point:
He is afraid of clowns.
This is referring to clowns in general, not any specific clown or clowns, and so an article is not used.