Why not fill a portion of the way, add the yeast, then finish filling the FV. That’s the method they recommend. Adding the addition wort halfway thru will knock the yeast down into contact with the beer.
Was there any mention of anticipated off flavors in the beer when dry pitching onto the foam? Any mention of how long the yeast had to sit on the foam before the off flavors were noticed?
I'll answer both of these by showing the whole exchange. The bold font is mine. (I originally just pulled portions to avoid cluttering the thread):
ME:
Your FAQ page answers the question "I see the recommended rehydrate temp for ale yeast is 25~29°C? My pitching temp for ale is 18°C. Will this not "stun" the yeast?". The Tricks and Tips page states "The temperature of the hydration media is between 10 and 28°C (50-82,4°F); and should ideally be close to fermentation temperature." This is lower temperature than the previous recommendation, and lower than shown on the FAQ page. It the lower temperature range a new recommendation?
FERMENTIS:
Thank you for contacting Fermentis. All our strains can be direct pitch into the wort, as long as the wort is between 10 to 28°C. That will not affect the yeast viability, vitality and resulting beer. If you want to rehydrate the yeast, also do it between those temperatures.
This is the latest information we have on our strains based on the latest trials. I apologize that there still is some potential confusing information in our written documentation.
ME:
Thanks for the explanation.
I'm planning on pitching direct (dry) for my next batch.
But I use top-off water, which I stir in before pitching. (In order to get 65F overall pitching temperature, the top-off water can be much colder or warmer than the wort from the kettle, depending on the season.) This prevents me from exactly following the instructions in the Tips and Tricks section: "To do so we recommend using the necessary quantity in weight of ADY and to put it into the fermentation vessel during the first part of the wort cooling step." The surface is very foamy. I'm concerned about sprinkling the yeast on the foam and leaving it, and my concern about contamination prevents me from waiting 10 minutes before stirring. I think gently stirring the yeast into the wort immediately after pitching would approximate the results that the instructions call for. Would this be correct?
FERMENTIS: Direct pitching is the method with the lower chances of contamination as there is no yeast handling prior pitching. But, in your case, with the presence of foam on the surface of the liquid is for sure not ideal. Sprinkling the yeast on the foam will leave some yeast outside of the liquid which is no good.
I will definitely rehydrate the yeast with water or wort in a sanitized container and pitch that slurry. If you stir, remember that is has to be gentle, max 100rpm on a stir plate or equivalent. Agitation (over 100rpm) during rehydration is the main cause of loss of viability in the yeast.
ME:
I understand my situation is not typical and greatly appreciate your giving me a "custom" answer to fit my circumstances. Great customer service.
Edited for clarity