Calculating ABV from Fruit Additions - An Actual Calculator

[Joe_CraftBeerTraders]

Hey guys,

So I have searched and read pretty much all the threads on here relating to ABV and Fruit additions. I have seen on both side, fruits are mostly water so its negligible, fruits cause re-fermentation so there must be an ABV adjustment. Well for the life of me I could not find a calculator out there or at least a better reasoning besides "its negligible". So I decided to build one myself to really see what the contributions are and if they are negligible.

Here is the calculator

http://blog.craftbeertraders.com/fruit-gravity-alcohol-calculator/


So some background behind what I did and the calculator. First, it DOES take into account the water addition from the fruit. Second, it uses Corn Sugar at 1.037 as a representation of fruit sugars.


Here is my approach. If you look at Corn Sugar for 1lb of Corn Sugar in 1 Gallon of water the Extract Yield is 1.037 or 37GU. So for every lb of Fruit Sugar I would have 37GU as well. But we all know that fruit is not all sugar. So I looked up what the sugar grams per 100grams of fruit was for each fruit. So lets say a fruit had 8 grams of sugar per 100grams of fruit. Thats 8% sugar. So for every lb of that fruit I know 8% is sugar or 37GU * 8%. That is what I determined was the Fruit Extract Yield.

But what about the water? Fruit is comprised of mostly water so how is that taken into account. Well we know that a Gallon of water weights 8.33lbs which means 1lb of water is .120 gallons. So I looked up what the % of water is contained within a fruit. Lets say a fruit was 87% water. That means 1lb of fruit will contribute 87% * .120 gallons.


And then thats it! You now have the calculation. You can figure out the sugar contribution with the water contribution to find the Expected Yield and then the Potential ABV.


So what doesnt the calculator account for. Well the first major assumption is that you are 100% efficient at pulling out all the sugar from the fruit. Second, you are converting all of that sugar to alcohol. Two pretty big assumptions but my goal was to be able to provide some type of calculator to let people determine on their own if they want to include the ABV or not.

Let me know what you guys think. I would love to discuss it with you all.

 

[Calder]

Two things I can immediatly think of:

- 1 lb of sugar from fruit will have 46 'GUs', or whatever it is. 1 lb of plain sugar in one gallon will yield 1.046.

- You do not account for the additional volume added with the fruit. Usually (depending on the fuit and OG of the beer), the gravity of the fruit juice/pulp is lower than the OG of the beer. The result being, you actually lower the abv of the beer by adding fruit. Your calculator gives the false impression it wil increase the abv.

 

[Joe_CraftBeerTraders]

Two things I can immediatly think of:

- 1 lb of sugar from fruit will have 46 'GUs', or whatever it is. 1 lb of plain sugar in one gallon will yield 1.046.

- You do not account for the additional volume added with the fruit. Usually (depending on the fuit and OG of the beer), the gravity of the fruit juice/pulp is lower than the OG of the beer. The result being, you actually lower the abv of the beer by adding fruit. Your calculator gives the false impression it wil increase the abv.

Im not sure I follow what you are saying. If you have 1 lb of fruit sugar and it yeilds 46GU that is the same as 1.046.

Second, what do you mean by additional volume? If you look at fruit it is a %of water, %sugar and the rest is solids, vitamins minerals etc. When looking at the way to calculate ABV its based off the amount of sugar and volume of water. The calculator takes into account the water addition of the fruit. The solids are not accounted into the calculation because it is not an addition in volume. If i put a block of wood into a beer when its fermenting it doesnt lower the abv because i increased the volume.

 

[Calder]

Corn sugar has an amount of water in it, so using it as equivalent to the same weight of fruit sugars is incorrect. You should be using 46 gravity points per lb of sugar, not 37.

When you add fruit or juice, it has a volume (of liquid). So your final volume after adding fruit will be greater than it was before adding the fruit. To properly estimate the abv impact of the fruit addition, you need to account for this increased volume, and also use the OG of the original beer, which your calculator doesn't ask for. I think you are assuming there is no volume increase.

If you account for the additional volume associated with the added fruit/juice, I think you will find abv will go down in most cases. And there is very little solid matter in most fruits, most of it is water, not wood.

 

[Joe_CraftBeerTraders]

Corn sugar has an amount of water in it, so using it as equivalent to the same weight of fruit sugars is incorrect. You should be using 46 gravity points per lb of sugar, not 37.

When you add fruit or juice, it has a volume (of liquid). So your final volume after adding fruit will be greater than it was before adding the fruit. To properly estimate the abv impact of the fruit addition, you need to account for this increased volume, and also use the OG of the original beer, which your calculator doesn't ask for. I think you are assuming there is no volume increase.

If you account for the additional volume associated with the added fruit/juice, I think you will find abv will go down in most cases. And there is very little solid matter in most fruits, most of it is water, not wood.

The calculator doesnt ask for the volume because it takes account the addition of volume into the equation. Each fruit you add has a % of water. Based on the lbs of fruit you add I calculate the gallons of water being added because of the fruit. I then use that and adjust the total volume before calculating the ABV. That is already built in.. Here it is from the OP

But what about the water? Fruit is comprised of mostly water so how is that taken into account. Well we know that a Gallon of water weights 8.33lbs which means 1lb of water is .120 gallons. So I looked up what the % of water is contained within a fruit. Lets say a fruit was 87% water. That means 1lb of fruit will contribute 87% * .120 gallons.

 

[TxBigHops]

Just ran across this while looking for something like it. Yes, I see that it's a 2 year old thread. Unfortunately I agree with the critical posts, and wonder if the author ever realized the flaw in his calculator.

Let me try to explain a different way. If you have a beer with an OG of 1.060, and you add fruit puree which has an OG of 1.045 (est based on a puree that I have used) you have LOWERED your OG, so therefore your final ABV will be less, UNLESS the addition causes your beer to ferment out to a lower ultimate FG. Which in my most recent case, it did. So what we need to do to in order to accurately compute the effect of adding fruit to the beer on the ABV, is recompute the OG change caused by the fruit addition. Then simply compare that recomputed OG to the final gravity of the fermented to to compute ABV.

 

[Joe_CraftBeerTraders]

It takes into account the water added by the fruit. So when calculating the alcohol it takes the sugar as well as the water from the fruit.

 

[TxBigHops]

It takes into account the water added by the fruit. So when calculating the alcohol it takes the sugar as well as the water from the fruit.

Yes, I can read. You stated that several times. You also said at the end of your first post that you would like to get the thoughts of others to discuss, and yet you stubbornly argue with anyone who has pointed out the issue with your calculator.

Your calculator even has watermelon, a fruit extremely high in water increasing the ABV. I can't get a single scenario to come up in which a fruit addition lowers ABV. So whether you believe it or not, there is a flaw in your formula. At some point, there has to be a fruit that increases the volume so much more than it increases the sugar content that the ultimate ABV is reduced, not increased. I would think watermelon would certainly be one of those fruits.

Another flaw is that your calculator doesn't ask for the OG of the wort that the fruit is added to. If you add fruit with an OG of 1.045 to wort with an OG of 1.030, then yes that addition will likely increase final ABV. If you add the same fruit to wort with an OG of 1.090, then it will most certainly lower the ABV. You can't compute an increase or decrease to ABV in a vacuum. You have to know OG before and after the fruit addition.

The only way I can come up with to do this correctly is to know the volume and total gravity points of the original wort, then the volume and total gravity points of the addition, and then recompute what OG would have been had they all been combined prior to fermentation.

 

[TxBigHops]

Let me try to say what I was just saying another way, with an example. Suppose you mash out 5 gallons of wort with an OG of 1.06. Then you also mix up a gallon of sugar water with an OG of 1.01. Surely you would agree that if you add the gallon of sugar water to the wort, that the resulting fermented beer would have a lower ABV than had you not added the sugar water. It's the exact same thing with the fruit addition. I think your calculator is probably computing the OG of the fruit addition, but without knowing the OG of the wort or beer it's added to, there is no way you can know if it increases or decreases the ultimate ABV.

 

[Joe_CraftBeerTraders]

I understand what all of you are saying but you are giving opinions on what you think. What would help is if you could explain it using the math. I'll put up the mathematical equation and logic I used.

The reason you don't need the OG and FG of the wort is because that is the calculated alcohol of the beer. What I am doing is looking at the fruit itself , the sugar contained and the water contained. And looking at if that fruit was fermented entirely how much alcohol would it produce.

 

[raysmithtx]

I don't know if this is correct but this is how I have been calculating my fruit additions.

Example
Estimates before adding the fruit
OG - 1.060
FG - 1.010
Estimated ABV% - 6.650%

If I added 2 pounds of Tangerines (normally about 11% sugar)with their normal sugar content of 11g of sugar per 100G of tangerines then I would be adding 98.8g of sugar and 710 grams of water for a total of 2 gallons of addition liquid.

So if I had 5 gallons of wort before the fruit addition then I would now have 7 gallons.

So I would have a total of 250 'points of sugar' from the original wort and now have added ~100 'sugar points' for a total of 350 points.

So 350 divided by the now 7 gallons of wort is 50 points. So in this case the tangerines would not add anything to the ABV%.

But if I added some sort of concentrated fruit then the results would be different.
If the tangerines were a concentrated puree of say twice the original sugar content then I would be adding 200 points of sugar in two gallons.

So I would have 7 gallons and 450 sugar points for a OG 1.064. So the tangerine concentration would have added 7.182-6.650=.532% alcohol to the beer.

 

[TxBigHops]

You want math. Here's math. The first pic is the spreadsheet calc I came up with to determine the effect of the addition of a large yeast starter and the raspberry puree addition. I used the OG and volume of each addition to compute total gravity points, and then used that to recompute the OG after the fruit addition as if I had added it prior to fermentation. The ultimate result is that the addition of the puree caused total ABV of the beer to go down by 0.03%.

And BTW, your last post was the first one that stated you were only computing the alcohol produced by the fruit. In every other post, and on your calculator you imply that the calculation provides the change to the ABV of the beer from the fruit addition.

So help me understand what you do with this number after it's computed. In my second pic, I put in the numbers from the raspberry hefe in the first computation. What is the significance of the 0.07 that was computed? What do you do with this number after it's been computed.

 

[Calder]

I think I see what his calculator is doing ...... but I'm not sure what to do with the results.

Say we have 5 gallons of beer, and we add 10 lbs of raspberries.

The 10 lbs of raspberries is ~1 gallon in volume, and ~180 grams of sugar (~0.4 lbs or 6.5 ozs of sugar). Using 1.037 for a lb of corn sugar (which I think is an incorrect baseline and should be table sugar at 1.046), you would get ~37x0.4 gravity points, or ~.015 points total from the added raspberries.

Now divide the 15 points by the 6 gallons (original 5 + the 1 from the raspberries) and you get ~2.5 points per gallon. The calculator says 2.7, but since I don't know his inputs for the fruit I think this is close enough. So per my numbers, the raspberries contributed .0025 points to the OG of the 6 gallons. And after fermenting out, the sugars in the raspberries contributed 0.32% abv to the final beer.

What the calculator doesn't do is calculate how much you diluted the original beer OG with the additional volume of water added. It gives the impression that you are increasing the gravity and therefore increasing the alcohol, when in fact in most cases you are actually lowering both. It doesn't even tell you how much the assumed added volume is so you can't even figure that out for yourself.

My conclusion is the calculator is useless for any practical purpose. And is inaccurate in what it does because it uses an incorrect baseline for the gravity of a pound sugar.

 

[Joe_CraftBeerTraders]

All good feedback. Sorry I haven't responded. Give me a little bit (probably tomorrow) and I will show you guys the calculations and what it's doing. If we agree it's wrong well fix it and get it to a state where we think it's right.

 

[bolus14]

Stumbled onto this and wondering if anybody has looked into this more. I'm looking to make a Troegs Mad Elf clone that will have roughly 4-6lbs of cherries being added and it would be great to know if the actually impact of the fruit. End of the day for homebrewers it's not the end of the world, some of us just like to know the ABV of our brews, I know some who no longer check the OG or FG...

 

[chickypad]

Stumbled onto this and wondering if anybody has looked into this more. I'm looking to make a Troegs Mad Elf clone that will have roughly 4-6lbs of cherries being added and it would be great to know if the actually impact of the fruit. End of the day for homebrewers it's not the end of the world, some of us just like to know the ABV of our brews, I know some who no longer check the OG or FG...

Follow the instructions on the mad fermentationist's page here. As folks mentioned the calculator in this thread is missing a variable. You need the 1) weight of the fruit, 2) brix of the fruit, 3) weight of the wort, 4) brix of the wort (or I guess you could do the calculations working with volumes rather than weight). The calculator wasn't taking into account the OG of the wort as previously mentioned.

 

[jespinet]

Hey guys... The part where I am getting confused with this conversation is this... I rack my beer off of the fruit into a keg (I'm sure you do too). So why does the volume of the fruit matter?

 

[chickypad]

Hey guys... The part where I am getting confused with this conversation is this... I rack my beer off of the fruit into a keg (I'm sure you do too). So why does the volume of the fruit matter?

There is sugar/wort left in that volume in the fermenter. Just like when you leave behind wort after racking, that is not all water you are losing sugars too (or beer if it's post fermentation). If you only account for the sugar content in doing your calculations that means you somehow expect to extract 100% of the sugar from the fruit, leave behind 100% of the water in the fruit, and not have any of your wort/beer get absorbed by the fruit. It doesn't work that way.