You can print QR codes for your tanks and barrels by going into new vintrace > Vessels page. Select the vessels you want to generate the QR codes for, then click on Actions > Print QR codes and select the size.
It will download a PDF of the QR codes. Below is a sample QR code.
You can then stick the QR codes to your vessels and then scan it from the vintrace app to bring up the current contents of the wine that is in the vessel.