Volume Markings for the 3 Gallon FerMonster

A problem with FerMonsters

I’ve been using FerMonster PET plastic fermenters exclusively for a couple of years. Many homebrewers might hesitate to use plastic instead of glass carboys due to the potential for small scratches that can harbor unwanted bacteria. However, from my experience of brewing over 50 batches with these fermenters, I’ve never encountered any issues with contamination.

There are so many reasons I love using these things. First off, the clear plastic makes it super easy to see what’s happening. I can usually tell which phase of fermentation my beer is in, just by looking at it:

Cloudy with no krausen? Still in Lag phase.
Cloudy and churning rapidly? Active Growth phase.
Less movement, reduced krausen? Stationary phase.
Becoming clear, with no movement? Conditioning phase.

Secondly, the wide-mouth lid makes it really easy to clean. To avoid damaging the plastic, I usually just pressure-wash them with warm-hot water from my sink faucet. If there is any leftover trub or krausen stuck in the grooves, I can reach my whole arm inside with a wet paper towel to wipe them clean.

But there’s also a big downside:
There are no volume markings to tell you how much wort you collected.

I decided to solve this problem!

tl;dr — my designs are available for download here.
If you’re interested in my process, read on!

Why does this matter?

This might not be important information for every brewer, but I like to gather as much data as I can, to track my overall brewhouse efficiency and final batch size for each of my brews.

If I am doing a split batch or a smaller batch than usual, where the wort doesn’t reach all the way to the top, this problem becomes way more apparent. For example, I have no idea how much beer is in these two fermenters:

Creating my own volume marker strip

I decided I would figure out how to create my own “volume marker strip” that I could apply to my 3-gallon FerMonsters, similar to these strips for the Spiedel 30L.

I attached a long strip* of painter’s tape to the fermenter, running from the center of the base, up the side and all the way to the neck. Carefully, I added water in one-quart increments and made markings on the painter’s tape.

* This actually ended up being three strips, because I was having trouble getting one single strip perfectly straight. I marked both sides of the “overlaps” so that I could stitch the full strip back together later.

I also added some extra markings for the various grooves and engravings on the fermenter, so that I would be able to align this strip accurately each time in the future. Without these markings, it would be hard to determine the proper vertical positioning of the strip.

I could’ve stopped here and had a functional volume marker strip for my fermenter. But I still had two other fermenters I wanted to add this to, and I didn’t want to go through this entire process for each of them. So I decided to turn this into a design I could replicate and re-use.

Creating a digital version

I laid out the completed template strip, and measured the value of each of my markings in inches.

It was important to get a number for each marking, because the scale between markings would not be uniform across the entire length of the strip. Near the base of the fermenter, the wall curves upwards. Along this curve, the volume does not increase linearly. Same too for the top of the fermenter, which curves back in towards the neck. The only linear segment would be the middle of the fermenter where the walls were perfectly straight.

From here, I took my values into Adobe Illustrator and designed a volume marking strip with cleanly written numbers and lines. Because this was now digital, for the linear segment of the strip, I was able to ensure perfectly even spacing between all the markings, even if they had been slightly off on my template.

The strip was too long to fit on a standard sheet of paper, so I split the design in half. Then I made sure each half had some overlap, so that they could be lined up and put together accurately. I was able to fit three strips on a single page:

Assembling the final design

For the material, I chose full-sheet (not pre-cut) waterproof vinyl sticker paper, because my fermenters would get wet frequently during cleaning and sanitizing. Then I printed out my design and cut each strip out separately.