What could cause a black line to appear inside a milk jug? We used the milk before noticing it was expired and there was a black line. After, new lower lines appeared
![What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting](https://i.redd.it/0vrbkj4oc0771.jpg)
What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting
![What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting](https://preview.redd.it/yi5k8fpq29871.jpg?auto=webp&s=5a17c2dc883f191ebd25ceaa2c687db6c5cfcb58)
What is happening inside this milk jug? Black lines have appeared at each level of usage. Milk is not expired and is put back into fridge immediately after each use. After posting
![Krystle Constantine on Twitter: "@Costco Bought milk from Costco. Something didn't look right. Look inside and see black rings that look like ink inside. What is this? Check your milk #Costco https://t.co/PTmpK0GKs9" / Krystle Constantine on Twitter: "@Costco Bought milk from Costco. Something didn't look right. Look inside and see black rings that look like ink inside. What is this? Check your milk #Costco https://t.co/PTmpK0GKs9" /](https://pbs.twimg.com/media/D6e-el6WsAAx4R_.jpg)
Krystle Constantine on Twitter: "@Costco Bought milk from Costco. Something didn't look right. Look inside and see black rings that look like ink inside. What is this? Check your milk #Costco https://t.co/PTmpK0GKs9" /
![Amazon.com: Normcore Handleless Milk Pitcher - Espresso Steaming Pitcher with Round Spout - 18/8 Stainless Steel Milk Frothing Jug, Black Non-Stick - Premium Barista Tools - Black - 15.2 oz (450 ml): Home & Kitchen Amazon.com: Normcore Handleless Milk Pitcher - Espresso Steaming Pitcher with Round Spout - 18/8 Stainless Steel Milk Frothing Jug, Black Non-Stick - Premium Barista Tools - Black - 15.2 oz (450 ml): Home & Kitchen](https://m.media-amazon.com/images/I/71RooCzc4FL.jpg)
Amazon.com: Normcore Handleless Milk Pitcher - Espresso Steaming Pitcher with Round Spout - 18/8 Stainless Steel Milk Frothing Jug, Black Non-Stick - Premium Barista Tools - Black - 15.2 oz (450 ml): Home & Kitchen
![Any idea what is happening here? At each line of use a black line has appeared inside the jug. The milk is not expired. It is placed back in the fridge immediately Any idea what is happening here? At each line of use a black line has appeared inside the jug. The milk is not expired. It is placed back in the fridge immediately](https://i.redd.it/cuckjkxv89871.jpg)