Both red diesel and white diesel can have up to 7% bio content. The bio content in diesel fuel is a substance called fatty acid methyl ester, known as FAME.

FAME is a bio diesel replacement fuel made from recycled cooking oils and a blend of other renewable and recyclable materials such as plant oils.

FAME is a good way to introduce renewable sources into the fuel supply chain but it does have some features which need to be managed. 

FAME:
1. is hydroscopic – this means that it attracts and holds water. This has a potential for mould, bacterial and algae growth
2. may be incompatible with some materials found in older machinery. Rubbers, plastics and surface coatings may degrade from contact with fuels containing FAME
3. can degrade over time by oxidation and hydrolysis
4. can suffer from cold flow waxing and precipitation problems

How to avoid issues with red diesel:
1. Buy from a reputable supplier
2. Have a tank suitable for the fuel and in good condition. Pipework and seals should be inspected and any deficiencies or damage remedied
3. Carry out regular checks and maintenance to help keep the tank in top condition
4. Keep fuel clean and dry and top up the tank to reduce air which may draw moisture
5. Fit a filter on the tank to catch any debris that may be present before it gets into the tractor tank
6. If you find sediment or bacterial growth seek professional help to remove and clean up the tank.