In Jainism, yeast is considered a very tiny living being (jiv), like other micro-organisms involved in fermentation.

Such micro-organisms are generally classified as ekendriya jiv – that is, they have only one sense: touch.

So, in Jain terms: yeast has one sense (sparshanendriya – touch), not five senses like humans and animals.

You can read more about sense-based classification of jiv and microorganisms involved in fermentation here