Double yeast pitch?

[Craig Howard]

Entirely academic question.

What "happens" if one pitched two different yeasts together? ie mixes yeast.

[David R]

Depends on the yeasts, and the beer I guess. It can be a valid technique depending on what you're trying to achieve. Have you ever tried Le Freak from Green Flash? I believe they pitch a Belgian yeast then 24 hours later pitch a clean US ale yeast. Not sure why, maybe to do with the hops, maybe to reduce the amount of fermenting the Belgian strain does to reduce it's influence on the beer?

An interesting experiment would be to brew two identical batches, split one and ferment each half with different strains then blend them once fermented, and pitch the same two yeasts into the other batch at the same time.

[Dave]

Here's an interesting recipe (From a reputable source so isn't just someone experimenting) that uses 4 different yeasts, added at different times during the fermentation.  

Bierre de Quattro

It's interesting stuff - here's the description of the yeast activities:

The first inoculation of yeast is Wyeast 3724 Belgian Saison. This strain produces the spice and earthy notes typical in this style. Fermentation should start within 6 hours, possibly sooner.

Six hours after you observe yeast activity, pitch Wyeast 3725 Bière de Garde. These are competing strains, but there is still a full dinner buffet of malt sugars available for the hungry yeasts. The character of earthy, spicy, and phenolics of the second yeast will be produced.

Give both strains another 6 or 8 hours, and then pitch Wyeast 3711 French Saison. Being a very high attenuator and a good producer of esters, phenols, and spice, this yeast will join the others gorging and finishing the malt buffet.