Yes, one packet (about one scant tablespoon) of active dry yeast has the leavening power of one standard cake of compressed yeast. Since compressed yeast contains 70 percent moisture (compared to only 8 percent for dry yeast), it must be stored in the refrigerator - and even then it loses its leavening effectiveness in about two weeks. Dry yeast need not be refrigerated, but it must be stored in an airtight container lest it absorb water from the atmosphere, rising its moisture content. That would reactivate the yeast's metabolic enzymes, awakening the dormant yeast cells.
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