From the Lallemond website;
https://www.lallemandbrewing.com/en/canada/products/brewing-yeast/
Also, download their
rehydration guide from the link above
Upon rehydration, dry cell membranes undergo a transition from gel to liquid crystal phase. Rehydration in sterile water is recommended prior to pitching into wort in order to reduce stress on the cell as it transitions from dry
to liquid form. Proper rehydration of dry yeast will produce a highly viable and vital liquid slurry.
The following effects have been observed with nonrehydrated yeast under specific brewing conditions:
• Longer diacetyl stand
• Longer fermentation time
• Longer lag phase
• Stuck fermentation
• Poor utilization of maltotriose
FOUR IMPORTANT FACTORS TO CONSIDER DURING REHYDRATION
1. MEDIA TYPE
Rehydration in undiluted wort causes osmotic stress to the yeast. Sterile water should be used for rehydration, but distilled water should be avoided.
2. TEMPERATURE
The ideal rehydration temperature is different for ale and lager strains. Ale strains should be rehydrated at 30-35°C (86-95°F), whereas lager strains should be rehydrated at 25-30°C (77-86°F).
3. TIME
The rehydration period should be between 20-60 minutes. A decrease in viability and vitality will result from extended storage periods after rehydration. Once rehydrated, the yeast can be pitched into wort. To avoid shocking the yeast, the temperature of the yeast should be reduced gradually to within 10°C (18°F) of the wort temperature. This can be achieved through additions of small volumes of wort to the rehydrated yeast slurry.
4. SANITATION
Care should be taken to avoid contamination during rehydration. The rehydration vessel should be autoclaved or sanitized before use. The outside of the yeast pack and the scissors/knife should be soaked in sanitizing solution prior to opening.