Can primary fermentation time be calculated?

[TonyP]

I've been wondering if it's possible to calculate the time to complete primary fermentation. For example, when we know starting specific gravity, volume, ambient temperature, and yeast brand / type can the time to desired ending specific gravity be determined?

The issue came up because I'm starting a Cru Int'l kit that estimates 14 days to get to 0.998 and I would have assumed more like 7-10 days.

 

[Rice_Guy]

There are norms which occur in fermentations, as a result the kit has a stated time.

There is enough variation as “did the kit get exposed to high temp which weakens the yeast” so it is not practical. It is exactly like the corona virus infection model, tweaking one variable a fraction can change the outcome a little or a lot.

 

[NorCal]

I‘ve made Cab Franc from the same grapes from the same vineyard for six years. If I pick on a Saturday, I‘ve pressed the following Saturday five out of six times. Last year the harvest was late and the garage temps were much lower and it took ten days to complete fermentation, which I was happy to see.
I think experience doing the same fermentation will be a better guide than a calculation.

 

[Scooter68]

There are just so many variables that can impact fermentation that 'calculating' fermentation time becomes unreasonably complex.
Finally why the need to know how long? Taking a trip while it ferments?

 

[BernardSmith]

I would presume a kit manufacturer is concerned that some people who buy their products have never made a wine in their life and so their kits and their instructions need to be designed to provide what is almost fail-safe information and processes. If a wine has completely finished fermenting in 7 days in a room with a temperature of 72 F it may take 14 days if the room is 60 F. And if it has fully fermented in 7 days there is little to no harm in allowing it to stand another week in the primary, all other things being equal. - but if the wine has not fully fermented in 7 days and the novice wine maker racks it , and in so doing racks it off the vast majority of the active yeast cells that wine maker may find him or herself with a stuck fermentation in the secondary... So , do you design in problems if you are the kit maker, or do you try to design them out?

 

[cmason1957]

I would presume a kit manufacturer is concerned that some people who buy their products have never made a wine in their life and so their kits and their instructions need to be designed to provide what is almost fail-safe information and processes. If a wine has completely finished fermenting in 7 days in a room with a temperature of 72 F it may take 14 days if the room is 60 F. And if it has fully fermented in 7 days there is little to no harm in allowing it to stand another week in the primary, all other things being equal. - but if the wine has not fully fermented in 7 days and the novice wine maker racks it , and in so doing racks it off the vast majority of the active yeast cells that wine maker may find him or herself with a stuck fermentation in the secondary... So , do you design in problems if you are the kit maker, or do you try to design them out?

Some of the kit manufacturers have gone to put a lid and airlock on your ferments, then wait 14 days and don't open the lid during that time. That seems kinda dangerous as well.

 

[BernardSmith]

But again, the kit makers may be calculating cost vs benefit. And what an experienced wine maker might view as an unacceptable cost because of the cost of the risk of doing nothing, the kit maker may view as a benefit because of the possible risks of doing something inappropriately. If your protocol is based on the lowest common denominator then you have "taken care of" rank novices and if the buyer is someone who knows her (or his) stuff then all you are really looking for is a source of quality fermentables.

 

[Scooter68]

Whoa - No Touchee while fermenting??? Nah not going to happen with me. As we all know there are so many things that can affect a ferment time and the outcome as well.
Juice buckets seem, to me at least, to be a challenge since so many talk about how they find that the fermentation is already underway when they receive the bucket. That's taking away or surrendering control of the set-up and conditions to someone else. That would be the biggest reason I would not order a bucket of any juice to be shipped to me unless it was guaranteed to arrive in a 'pre-fermentation state.' I might want to make adjustments. For beginners fine, if they don't want to be involved in taking measurements and adjusting, but I don't see how you would learn much that way.

 

[bstnh1]

I've been wondering if it's possible to calculate the time to complete primary fermentation. For example, when we know starting specific gravity, volume, ambient temperature, and yeast brand / type can the time to desired ending specific gravity be determined?

The issue came up because I'm starting a Cru Int'l kit that estimates 14 days to get to 0.998 and I would have assumed more like 7-10 days.

There's a surefire way to calculate the time to complete fermentation. Step 1: Record the date you pitch the yeast. Step 2: Record the date when fermentation stops. Step 3: Count the days that have elapsed between step 1 and step 2. The result is the time required to complete fermentation.

 

[winemaker81]

@TonyP - the succinct answer to your question is "NO"!

The best answer is use bstnh1's method.



In addition to the items you mentioned, we have to figure in pH, TA, SG, how stable the temperature is, the phase of the moon, the average weight of a male African swallow, and a probably a few dozen other factors.

The fastest ferment I've had is 4 days, the longest a month or more (mead). Most are 5 to 10 days.

I'm being (irritatingly) facetious .... but the real answer is to control the factors you can and accept that yeast is gonna do what it's gonna do.

 

[montanarick]

Amen to that. I generally see a five to six day ferment when I keep temps at around 80 degrees with reds. It will go considerable longer with whites where temps are kept around 70. Good luck

 

[TonyP]

Thanks for all the responses. Although no one suggested fermentation time can be calculated within a reasonable range and I don't know how to do it, I'm confident it can be done. Virtually all winemakers know temperature impacts fermentation and that wine ferments more slowly at lower temperatures. The amount of yeast used in a volume of must can be calculated. Specific gravity can be determined.

There are many variables in fermenting but all are either known or can be determined. Likewise the impact of those variables is known. Given that fermentation has limited variables, fermentation time seems to me to be calculable, although I can't do it.

 

[winemaker81]

You have to take into account the yeast variety, it's "eating habits", the amount of food (for the yeast) in the must, components that will enhance OR restrict yeast eating, etc. While those factors can probably be determined in a lab (which home wine makers won't have), yeast is a living entity that will not necessarily behave in a consistent manner.

It's an interesting idea, but there are many uncontrollable factors. Please report your findings as you develop a formula.

 

[TonyP]

It's an interesting idea, but there are many uncontrollable factors. Please report your findings as you develop a formula.

Attention viticulture / enoology students looking for a project ...

 

[Ajmassa]

NorCal said it well, “experience would be a better guide than calculation.” Plus a theoretical* calculation would take a lot of the fun out of it for the winemaker.
but just for fun here’s a list of all the things that likely factor into it if it could be done.

yeast selection
Amount used
Hydrated? Distilled, tap, spring water?
Grape volume
Ph
TA
Brix
Glucose, fructose levels
So2 added?
Enzymes?
YAN level
Nutrients used, amount, timing of additions
Ambient temperature
Probably barometric pressure & humidity too
Punchdown/pump-over frequency
Type of vessel (cap thickness/surface area)

I’m probably missing a lot too. Regardless of practicality it might be a fun little challenge for a wine & science nerd with some time to kill.