10mg. It could be something else in my diet that contributed to the gas last night, but so far, it's a bit better today.
Sulforaphane is powerful, you have to be careful. If the gas doesn't eventually go away at any dosage level, then you might have sulfur intolerance, which is usually a result of dysbiosis. There is also a small number of people out there who can't tolerate sulforaphane whatsoever and it's not gut flora related. These individuals usually have poor genetics in their transsulfuration pathways.
It's also a strong detoxing agent. It is primarily absorbed into the liver where it is used to remove toxins down to the intracellular level, which can prompt liver cells to produce more glutathione in those who have the strong capability. It has activity on heavy metals, for example. This is another reason to be very gradual with sulforaphane.
On the gut level, it causes shifts in the gut flora toward butyrate-producing species. The shift in gut flora composition will naturally produce gas as some species die back. If you start at too high a dose, this shift can be too radical, releasing too much LPS from die off, triggering flare conditions. Sulforaphane is itself an anti-inflammatory so when used gradually it will help UC. The exception is if you have really bad sulfur intolerance. You'll know because you can't eat any cruciferous vegtables without problems, flare or no flare. If you can't consume sulfur foods during a flare but you can when you're not flaring, then your problem is likely dysbiosis and sulforaphane can remedy some of that over time.