How grow several varieties of barley without cross breeding?

[sugarworm]

I'm planning to grow a barley seed crop for home-brewing later on and I got three different breeds from my brew shop started together in a raised bed that I'm planning to transfer out after I realized that there might be some accidental cross breeding. Barley's self pollinating, but what's a safe distance so there aren't any chance of hybrids?

[lorax]

Distance isn't the factor to worry about here. Timing is. If you've got different types of barley, what to look for are types that mature at different rates - that way only one type will be producing pollen at any given point, and no hybridization will occur.

[GardenGnome]

For pumpkins and its family they say 100. But I bet that's not fool proof. One little bug that goes that extra way will mess it up. But what lorax say sounds like the number 1 answer. But your doing yours in the same bed do you grow your own hops also?