The traditional recommendation that mussels should only be consumed in months with the letter “R” has traditional backgrounds. In our latitudes, mussels are in season from September to April and are mainly offered from German and Dutch harvests. Shellfish poisoning only occurs in hot months (without the letter “R”) because algae bloom in these months and produce toxins during bloom.
Toxins in algae
Through filtration processes, mussels absorb the algal toxins with the water. The toxins can thus accumulate in dangerous concentrations in the shellfish. This process is called “shellfish poisoning” and is reflected in popular wisdom. Furthermore, in the past, worse storage and transport conditions prevailed, which were more likely to lead to spoilage. Thus, it was only logical to avoid shellfish during the hot months.
Year-round control
Today, comprehensive EU legislation ensures that throughout the year both coastal nursery areas are controlled with regard to algae and bacteria, and all coastal areas relevant to the harvesting of mussels are controlled via an early warning system for algal toxins.
In the purification and packaging centers, the mussels are only released for consumption after they have been checked for safety. This largely eliminates the possibility of consumers’ health being adversely affected by algal toxins and by harmful bacteria.
Background information
In the past, the “R” rule made sense because toxins from algal blooms, which often lead to shellfish poisoning, were a major problem. This natural phenomenon only occurs in summer months, as algal blooms and associated toxin formation do not occur in winter.
Mussels, through their filtering activity – a blue mussel filters up to 2 liters of water per hour – absorb the highly toxic algal toxins of the armored flagellate algae with the water. This can result in dangerous concentrations of toxins in the mussel, making it unsuitable for consumption.
Today, the risk of shellfish poisoning from algal toxins or bacterial spoilage is very low during the warm season. Harvested mussels are stored in special seawater sections on the coast, called wet warehouses, until they are transported. Here, natural purification takes place as the mussels excrete sand and other impurities. In addition, modern distribution methods allow for a closed cold chain. Still, mussels are a perishable food and consumers should be aware of a few things when purchasing and preparing them at home.
Tips for consumers
- Refrain from eating in the summer (June, July, August) if necessary, as the mussels spawn during this period and their taste may be affected.
- Freshly purchased mussels store refrigerated and consume no later than the next day.
- For preparation, use only closed mussels and consume only the opened mussels after cooking.
