How did I miss my Original Gravity? Why did I only end up with 4.5 gallons of wort?
I often see first-time homebrewers asking the same questions regarding their recipe “numbers.” There are many answers to the questions above, but I’ll let you in on a little secret – put ANY brewer on a new brew system and they will have trouble predicting, and hitting, their numbers on their first batch.
Why? Because every brew system has key components which will affect the resulting beer. Experienced brewers have made many batches on their system to identify these areas and plan for them in future brews and recipes. The key to “hitting your numbers” lies in taking detailed notes and recording accurate measurements
The most important of these measurements is volumes!
Knowing the volume of liquid you have at the different stages of the brewing process is paramount to achieving your desired gravity. The reason for this is that once in the boil, the wort contains a set amount of sugars. It is the concentration of these sugars that will determine the original gravity. The concentration is directly correlated to the volume.
Your volume is affected by the following input and output variables:
- Mash Water
- Sparge Water
- Top-off water
- Grain absorption
- Dead Spaces (in kettle, mash tun, HLT)
- Evaporation from boiling
For the inputs, you need to have an accurate measurement tool. Whether you use a sight glass or measure your water out in one quart increments, you need to know how much liquid you have during your process.
When designing a recipe you need to have a grasp of the input and output volumes to proactively make adjustments on brewday.
Nailing your O.G.
For example, if you know you always have deadspace losses in your system of .25 gallons, evaporation of 1.25 gal per hour boil, and 1.5 gal grain absorption (for a 12lb grist), you will need an extra 3 gallons of water allocated to your inputs to reach your desired final volume.
Want to end up with 5 gallons after the boil? Then you need a total of 8 gallons of input water for that beer.
You can also use this information to make sure you are on pace to hit your original gravity. Since your boil-off rate is 1.25 gallons per hour you can figure out what your gravity will be at the end of the boil. Just take the pre-boil volume and multiple by the gravity to get the total gravities points. Then divide those total gravity points by your predicted (1.25 gallons less) post-boil volume. If the gravity is too high you can add more water to dilute the wort. If the gravity is too low you can add DME to increase the gravity.
So as I mentioned at the beginning, even a pro would have difficulty hitting their numbers the first time around. The key to figuring it all out is to make a sacrificial batch of beer and be diligent with recording your volumes at every step of the process. Be precise and note how much is going in, and how much is goin out.
Record and analyze this data and you will be ready for the next beer where you can nail any recipe on your system!