RoomWithABrew
Landlord.
Subtle difference, but you are right don't add it to the beer.Don't add it to the beer at all. Just a small sample of the beer, a teaspoonful is enough, and then throw the sample away.
Back in the day when a 90 minute mash was standard, I had, perhaps, one in 20 brews where I had to extend the mash time to complete conversion. Now that recipes are calling for a 60 minute mash, I would have thought the starch test was even more important. Unless you're brewing a hefeweisen or one of the cloudy, alcoholic fruit juice non-beers, of course.
Vosene more suitable for a 90 minute Wash.
https://www.vosene.co.uk/