I’ve made my fair share of melomels and have noticed that some of my batches have a strong fruity taste while others are lacking in that department. At first I did not know why since I strictly adhered to the recipes. It wasn’t until I did my research and learned that I NEEDED to punch down the “cap”-the layer of fruit in the primary of a melomel. Below the cap, your must’s temperature can range between 104-106 degrees F. This level of temperature kills the yeast, interrupting the fermentation process. Flavors will be lacking and instead you will get off flavors with your batch. Punching down the cap also allows the fruit to thoroughly mix within the must and thus leading to the vibrant colors, fruity aromas, and fruity flavors that characterize a melomel. The yeast will also be more evenly distributed since the highest concentration of yeast is directly below the cap.
There is also a CO2 buildup directly below the cap, minimizing the amount of oxygen that the yeast is receiving. This deprivation of oxygen (which is an important yeast nutrient) will weaken the yeast’s cell membrane. The yeast will therefore not be performing at its highest capability and fermentation will be stressed. There is also a sanitary reason to punching down the cap layer. Microorganisms can live on top of the dry cap and completely spoil your mead.
You want to use a metal masher rather than a wooden one since bacteria can live in the porous structure of wood. It is recommended to punch the cap about 3 times a day during active fermentation. I personally punch the cap less frequently just cause I’m worried about introducing bacteria everytime I open the carboy. During the process the temperature of your must should be about 60-65 degrees F. Also don’t forget to sanitize the instrument you are using to punch down the cap.