So this is why you DEFINITELY need to use a cleaning brush with your stainless steel straws... Before and after pics of the white brush, eek!
We've seen it said elsewhere that you don't need a brush, just wash in hot water and/or a dishwasher and you'll be fine.
But these straws have been in hot water and the dishwasher a few times and still had this gunk.
So definitely make sure you get a brush with your straws and do use it
We've also now added replacement cleaning brushes for stainless steel straws (both standard and smoothie) on our website after our recent cleaning experiment (link below)
So definitely get a cleaning brush and do use it!