Theoretically you could breed (or possibly GM) a particular strain of yeast, and patent that for a particular use, but you'd need to pass certain thresholds of novelty in the application, not just the resulting taste. I don't think you could do that with just yeast for simple brewing, because wild brewers have almost certainly already used your strain in some form.
OTOH, commercial brewers might choose to make their yeast available to someone for yeast banking under a trade secret type NDA. Selling that yeast to other brewers would be a violation of the NDA. But if you didn't sign one, then you probably aren't covered by it (IANAL - see your lawyer if you are thinking of a specific case).
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