No More 12 Hour Filtrations

Change has come to Pennichuck’s bottled beer… Within the last month, we have been researching a new to us form of filtration. Since our inception a little over two years now, we have been filtering our beer using a plate and frame filter. These filters use pads that are composed of cellulose and diatomaceous earth (DE). For our filter, it takes (39) 40x40cm pads to push 30 barrels (930 gal) through within 8-15 hours! After spending Christmas Eve at the brewery, I made it a personal quest to figure out how to filter with a DE filter.

A DE filter is MUCH more complicated than a plate and frame filter, but the time saved is worth it. DE or diatomaceous earth are basically microscopic seashells. The nooks and cranny's that make up the shells are excellent at trapping single-cell organisms such as yeast. DE comes in a powder form that we mix with beer or de-oxygenated water. In the powder form it presents some health hazards to us, but as soon as it mixes with a solution such as beer, it is no longer dangerous. Below is a microscopic view of DE.



There are two types of DE filters. There is a vertical leaf filter and a horizontal leaf filter. We have a 3 sq. meter horizontal leaf. The leaves are plates with a fine mesh screen. Prior to filtering, the leaves need to be coated with a coarse layer of DE to prevent yeast and other particulates from passing through the screens. This coating is called the precoat. Many breweries differ in how they precoat in regards to composition, ratios, and amounts. For us, we like to use a little bit of cellulose to provide a flexible bridge across the screens to help prevent any breakthrough. We then finish the precoat with a coarse DE followed by a fine DE layer.

Once the precoat has been built up, which takes about 15-20 minutes. We know when the precoat has been sufficiently established because the cloudy beer that we used to mix the precoat compounds will turn clear (bright) in the sight glass. After the precoat is established, it is time to bring in the beer and begin filtering. While the beer is being passed through the filter, there is a small dose of DE constantly being added to the filter to provide a new filtration bed. It helps prevent the heavy yeast load from building upon itself, creating a blockage. This is what typically happens with a plate and frame filter.

We ran a trial batch through the filter a few weeks ago with moderate success. We managed to filter 15 barrels in two hours. For us, that was a huge success, but for a DE filter, that time should have been cut down to only one hour. We went back and looked at our precoat ratios and our body feed amounts to find any areas for improvement. After talking to a few other brewers, who were immensely helpful, we realized where we needed to change. After making the changes, it was time to filter our first 30 barrel batch. It was nerve wrecking. The thing about a DE filter is that if you mess up your filter bed, you have just added 3 more hours to your day redoing everything. Well, we successfully filtered 30 barrels in exactly two hours. This was the flow rate that should have been expected in the previous filter run.

After successfully filtering 30 barrels in only two hours, we realized there is no going back. What this means to the consumer, is that we have greater control over our packaged product. With DE filtration, we can zero in on how many microns we want to filter down to. We can also add in stabilizers to increase shelf-life. With the plate and frame filter, our pads were constantly inconsistent with the specs. In the last two filtration runs with the plate and frame, we were getting yeast breakthrough into the packaged product. This leads to a hazy beer.

So drink up and enjoy!

James