I reviewed the information I'd got when I visited the brewery and this is very much what they do there:
- Mash at 60°C so there's maximum fermentability for the primary fermentation with Saccharomyces.
- Include a large proportion of 100% fermentable sugar for the primary fermentation.
- When bottling the beer pitch 99% Saccharomyces and 1% Brettanomcyes for the secondary fermentation.
Armed with this knowledge my latest attempt at making an Orval like beer had a long and low temperature mash, with a very small Brett. addition on bottling...and it worked! I got a crisp tasting beer with a touch of funk and no nitrogenation. I'm rather pleased with this one.