## 4 Discussion  
Our experiment showed that using conventional methods, it is possible to obtain about 40 g of pure meat from 1 L (290 g) of fresh mussel-mass cultivated in the low-salinity conditions of the Baltic Sea. This is about 2-3 times lower amounts than observed in fully oceanic waters [25]. Moreover, the shells of the Baltic Sea mussels are smaller, and they are much thinner compared to their counterparts in oceans [26; 27]; thus, the traditional processes that are used to effectively separate meat from intact mussels in other seas cannot be used in the Baltic Sea region. Our study also revealed that the separation of meat from fresh or frozen mussels can be achieved by simple means without requiring overly complex and expensive machinery. Simple and industrially scalable technology (i.e., crushing and sedimentation) allowed us to extract a significant amount of meat with a high protein content (i.e., half of the total protein found in the used mussel-mass). Importantly, the mussels need to be crushed with water. Optionally, the biomass could first be heat treated to minimize foam formation during the homogenization process. The meat is light and sinks slowly in the water column, while the shells sink quickly. This helps to separate a significant amount of the mussel meat through simple sedimentation. However, the technology can be further improved, and thereby the dry matter separation performance can be optimized even further. The experiments showed that both the ratio of raw mussels to water and the subsequent sedimentation time significantly affect the protein and dry-matter contents of the separated suspension. A 15 min exposure time allows significantly lower calcium concentrations to be achieved compared to 1 and 5 min exposure times. Therefore, 15 min is the preferred time for lower-calcium yields. Lower-calcium yield is often a desired outcome when extracting meat and protein mass, as it increases the quality of extracted products. However, a longer sedimentation time will also reduce the protein content, with an estimated 1.5-fold difference observed between 1 min and 15 min sedimentation times. Nevertheless, the calcium content of the Baltic Sea mussel shell estimated in the current study was about two times lower than estimated in oceanic waters [25] and this difference is caused by low salinity [28]. Reduced salinity is coupled with lower availability of calcium and inorganic carbon in seawater, which often results in thin, small, and fragile shells of mussels inhabiting the Baltic Sea [29]. When Baltic mussels are moved to more saline environments, they grow larger, indicating that the rate of calcification and maximum shell size depends on the environment [30]. Moreover, one of the most striking features of the Baltic Sea is low predatory pressure on mussels, and this is another reason why  
Figure 5: Average content of dry matter and the content of proteins in dry mass with 95% CI (%) among different treatments. The mean values with different letters are significantly different from each other at \(p<0.05\). N indicates the number of replicates. mussels do not have to invest in thicker shells and their morphology differs between the Baltic and higher-salinity seas [31]. Lower calcium content and more fragile shells make the Baltic Sea mussels better material for meat and protein extraction compared to their oceanic counterparts. Even if higher calcium content was measured at shorter exposure times, the concentrations are not too high to cause a significant deterioration in product quality during the industrial extraction of meat and proteins. It also became clear that the filtration resulted in high losses of the dry matter and protein content of suspension. Averaged over all samples, only 20% of the proteins that were present in the manually separated meat were recovered after filtration. One-third of the protein originated from the settled shell material that partly contains meat.