Since I started making mead in November, 2008, I have approached it with an attitude of experimentation. My goals: 1) Keep it cheap until I know if I want to stick with it; and 2) Try several recipes to discover what kinds of mead I like.
Let's focus on my cheapness goal: So far, the only pieces of equipment I've purchased are clear, plastic tubing to use for racking and a thermometer (which I used once and now realize was unnecessary). I don't have a hydrometer, a real carboy, a fermentation bucket, fancy disinfectants, an airlock, filtration devices, Camden tablets, or dedicated stainless steel crockery. I've gotten by on milk jugs, balloons, my wife's cooking pots and rubber bands (and I've discovered the rubber bands are unnecessary as well).
I like to think of it as "Mead-making: MacGyver Style." It's not a method I invented myself. This guy gets credit for giving me the blueprint and answering my many questions. And a detailed description of the process is here.
If you read the process description, pay special attention to how I use a balloon as an airlock, stretching it over the mouth of my jug. A pin-hole in the balloon allows CO2 from the fermentation process to escape, and the positive pressure inside the balloon keeps contaminants out. This will be important to understand in just a moment.
When making my mead in milk jugs, I would gage the vigorousness of the fermentation with a little device I like to call "my ear." I could walk into my bedroom closet where I keep my brew and listen. The fermentation was quite audible, and it slowly would become less audible as the primary fermentation slowed down. An excellent -- and cheap -- method, if I do say so myself.
However, I recently started a new experiment. Now that I have my base recipe defined, I've decided to scale up to a 5-gallon batch. So, I obtained a 5-gallon plastic water bottle -- the kind that you set upside down on a dispenser. The problem is, this bottle is made of much thicker plastic than the milk jugs, and I can no longer hear the fermentation. This threw a wrench in my methodology. Being unwilling to purchase an actual airlock so that I can count the bubbles or a hydrometer so that I could... um... do whatever you do with a hydrometer, I decided to invent a new way to gage the strength of the fermentation process.
After thirty seconds of intense contemplation, I figured it out. I pulled out my cell phone and, using its handy menu system, navigated to Tools > Stopwatch. Then, I squeezed all the air out of my balloon, started the stopwatch, and waited for the balloon to inflate again. As soon as the it popped upright, I stopped my Fermentation Vigorosity Indicator (FVI).
Now, I can reference my measurement to the ones I take in coming weeks to gage the health and stage of the fermentation process. Also, by comparing previous measurements with future batches, I'll be able to tell if the future batches are on track. Sure, there is still an element of good ol' fashion dead-reckoning going on, but it is a compass of sorts that will suffice until I'm ready to wax sophisticated.