We do our best to insulate liquid yeast packs in a bubble wrap envelope but you'll have a much better chance of viability if you select an ice pack in the accessory list. During cooler months, a single ice pack is enough for up to three packs of yeast. In the summer, you may want several ice packs for a single pack of yeast and coordinate the shipping with us to avoid long periods in a delivery truck.
WHAT ARE THIOLS AND WHERE DO THEY COME FROM?
Volatile thiols are highly impactful aroma compounds that evoke grapefruit, passion fruit, and guava and are found in a variety of tropical fruits, wine grapes, and hops. These thiol compounds exist in two forms — free forms, which are highly aromatic and volatile, and precursor forms (i.e., glutathione- and cysteine-bound thiols). The precursor forms, abundant in malt, are non-aromatic and require yeast with β – lyase biotransformation activity to release them. Hop varieties vary widely, not only in the amount of thiol compounds, but also the percentage that are in the non-volatile precursor form. New World hop varietals, specifically Southern Hemisphere hops, appear to be the highest in free thiols, which contribute to their characteristic tropical fruit aromas. The precursor for 3‑sulfanyl-1-hexanol (3SH, but also referred to as 3MH — a thiol known for its intense grapefruit and passion fruit aromas) is abundant in barley, but does not reach sensory thresholds until converted to its free form. In beer and wort, the overwhelming majority of these thiol compounds are in precursor form (1000-fold!) and are a stockpile of aroma potential with a yeast capable of biotransforming them to the free volatile and aromatic thiol compounds.
HOW WERE THESE STRAINS DEVELOPED?
Our R&D team became curious about thiols and methods for making the process of freeing thiols more efficient. We dug into the literature and focused on IRC7, a gene in yeast that encodes an enzyme (β – lyase) that frees thiols from their precursor form. The problem, however, is that many brewing strains have mutations in the IRC7 gene that disable the enzyme, and those strains that do have a functional IRC7 gene don’t make the enzyme in wort because high nitrogen levels (like we see in wort) turn off the gene.
We explored the possibility of altering the IRC7 promoter (the sequence that controls the gene’s expression) to a version that would keep the gene active at all times, even in a high-nitrogen environment. By finding a way to keep the IRC7 gene functional, we should theoretically be able to unlock thiol precursors and derive more flavor and aroma from our malt and hops.