Is there a good way to estimate/calculate volume lost in fermentation(s)?

Question

Last night I bottled a batch and realized that I lost a significant volume from the boil size. In the primary, I filled my 6 gallon carboy, and after the trub lost in primary and secondary, I bottled just under 5 gallons of beer. Which means, I lost an average of 0.5 gallons per fermentation stage.

Is anyway to estimate the volume lost other than by empirical methods? Does the OG, FG, or type of yeast play a predictable role in this? Would I have lost the same volume had I not transferred to secondary?

I realize this is a normal loss, this is purely a question of curiosity.

some numbers, if they help:

• Vol in primary: 6gal
• Vol in secondary: ?
• Vol bottled: 4.83gal
• OG/FG: 1.054/1.012
• yeast: US-05

Answer 1

The best approach is to take a lot of measurements of your equipment and of actual volumes.

1. Measure the amount of water you put into your HLT
2. Measure remaining water in HLT after 'empties' after sparging (for instance)
3. Measure the pre-boil volume in your boil kettle
4. Measure the post-boil volume in your boil kettle
5. Measure remaining trub from your boil kettle (just pour it into a kitchen measuring cup, and if you bag your hops, toss the bag in there too!)
6. Measure the volume in your primary fermentation vessel
7. Measure the volume of the trub/yeast from primary (again, measuring cup)
8. Measure the volume in your secondary fermentation vessel
9. Measure the volume of the trub/yeast from secondary
10. Measure the volume that gets into bottles

The difference between 1 and 2 is the dead space in your HLT. 1 minus both 2 and 3 tells you water absorbed by grain and dead space in your MLT. 5 tells you loss to BK trub. Loss to cooling shrinkage will be 4 - 6 - 5. The rest are pretty obvious. What I have done is very carefully mark a pitcher with exactly a gallon, then use that to make marks on my tuns and vessels. It's pretty easy to see 1/4 gallon differences, even 1/8 gallon differences. For the containers with vertical sides, I've calculated how many centemeters is a gallon, and so you might find in my brewing log (4 + 13/17) gallons noted, for instance.

Once you have these values, they should be good for beers with the same or similar amount of hops; styles with more hops would likely loose more in the boil and fermentation (if dry hopping). If you kept track of hop usage over several batches with varying hop weights, you could probably come up with a formula to adjust for it.

Answer 2

I don't know of a universal rule -- everyone's setup is just too different. The best approach is probably to track, as best you can, how much beer you have at each stage. After doing this for several batches you'll have a good estimate.

Even with the estimate in hand, your loss is going to vary from batch to batch. A high-gravity beer will have more fermenter trub than a low-gravity beer, for example.

And I'd guess that you would not have lost as much if you hadn't moved to secondary. Every racking leads to loss somewhere.

Answer 3

I think common wisdom is to shoot for at least half a gallon more post boil per 5 gallon batch to account for losses. I add one gallon, so I brew 6 gallons to package 5, or 12 gallons post boil to package 10 gallons.

You might be able to work out something for your system if you brew the same beer over and over, but doing this for continually varying brews will require a lot of effort - there are many variables to track, and it's not something that's been widely documented, since it varies so much from system to system.

If you made meticulous logs and came up with a theory to accurately account for boil (hop absorbtion) and fermentor losses (trub, racking, dry hopping absorbtion, hydrometer samples), you might be able to get some reasonable figures. IMHO, a lot of effort for saving half a gallon of beer per 5 gallon batch!

Regarding hop losses, dry hops absorb at least 4 times their own weight of wort. That's the only figure I can think of that might help you account for some of the losses.

Answer 4

You could try marking the carboy with known volumes. I ferment in a 5L jug and I measured and added 0.5L of water at a time and marked on the jar with a marker where the water level was. It's not precise enough to be used in a lab, but it's good enough to help make a good estimate for how many bottles I'll need.

Answer 5

I'm newly signed up on homebrew.stackexchange so I'm limited in where I can contribute. This is not so much an answer, but an elaboration of the question.

I was thinking it would be useful to understand an ideal water, sugar, yeast system. For wine making, one might assume 80% sugar conversion during primary ferment. You'd need to estimate how much yeast is produced, and how much precipitates out of solution. The discarded lees will have a certain minimum hydration level, which you'd need to input empirically.

Perhaps it is hard to estimate total yeast production. What is the rate limiting parameter? Is it yeast population density, or one of the yeast grown reagents (oxygen/nitrogen/trace nutrients)?

Skimming Yeasts & Primary Fermentation, this text indicates that cultured yeast fermentation usually starts around 5 billion yeast cells per litre and hints that available oxygen is one of the primary growth limiting factors (for fermentations that don't get stuck). It goes on to say that total yeast populations for wild ferments tend to be lower than for cultured ferments, so I'm guessing that lees production would be less as a result.

A kit wine maker I'm presenting using allows for an addition of 920 ml of water to a fermentation that begins at 23 litres, to make it up to the desired end volume. I would guess the 920 ml covers various process losses, such as CO2 release, lees production, and evaporation. These kits are engineered to known initial parameters and use extremely predictable yeasts. They have less control over brew temperature and hose jockey slurpage ratios (the recommendation is to slurp from primary just about everything that will go up the tube).

I've consistently found with these kits that I'm about a litre short from 2" below the bung after regulation top-up, even with aggressive slurping. My two recent vintage Italian carboys measure 23.9 kilograms of room temperature tap water (+/- 20 grams). The extra 900 ml of head space is really driving me crazy. I've seen it written elsewhere that recent vintage Italian carboys average closer to 6.25 US gallons (my measurements work out to 6.3 gallons to my desired fill level for secondary ferment).

Anyway, I wanted to look at the fermentation math as part of my dialog with my kit vendor and I found this post. It does seem rather empirical for less controlled scenarios.

(I'd be grateful to anyone who votes me up to the normal minimal level of useful participation. Less crippled I can earn my keep.)