The issue is that many people mistakenly assume that they can determine how much gravity the fruit will add by calculating the amount of sugar it contains. The problem with this method is that in addition to sugar the fruit also contains water (which dilutes the alcohol/sugar already in the beer). In fact, most fruits have a similar sugar content to a standard gravity wort, between 1.040-1.060. There are some exceptions, for example in a couple days I'll be getting 5 gallons of Cabernet Sauvingon grapes (to add to sour beers) that have a sugar content of 22 Brix (1.092). Concentrated and dried fruit are another exception because most of their water content is removed during processing.

To correctly determine the impact on the alcohol content of adding fruit you need to determine the effective brix/plato of the beer. To calculate this you need four pieces of information:

1. Weight of the fruit (not including pits/stems/seeds).

2. Brix/plato of the fruit (from a refractometer or packing info).

3. The original brix/plato of the beer (OG reading).

4. The weight of the beer (based on the current volume, but the density of the wort before fermentation. This can be determined by using the following formula: weight of the beer = original gravity of the beer x volume of the beer x weight of 1 gallon of water)

Effective Brix/Plato = (Weight of beer x Brix/Plato of beer + Weight of fruit x Brix/Plato of fruit) / (Weight of beer + Weight of fruit)

For example if you have 4.5 gallons of 11 P (1.044) beer it would be 1.044*4.5*8.35

**= 39.2 lbs of beer onto 10 lbs of 14 P cherries, the effective OG would be (39.2*11+10*14)/(39.2+10) = 11.61 P. That is to say the increase in the effective starting gravity was .61 P, enough to boost the alcohol by .3% ABV assuming the same FG (about the same increase in alcohol from the priming sugar).**

On the other hand if you add the same 10 lbs of 14 P cherries into 4.5 gallons of 25 P (1.106) Imperial Stout you would have 1.106*4.5*8.35

**= 41.6 lbs the equation would be: (41.6*25+10*14)/(41.6+10) = 22.9 P, a drop of 2.1 P, enough to reduce the alcohol by 1.1% ABV assuming the same FG.**

These two examples demonstrates a key insight, if the gravity of the fruit is lower than the original gravity of beer the addition is going to lower the effective original gravity and thus reduce the ABV (and conversely if the gravity is higher it will raise the effective original gravity and similarly the ABV).

In general fruits provide sugars that are more completely fermentable than malted/mashed grains, so even with the same OG you may end up with a lower FG and thus marginally more alcohol. That said, if you determine your effective OG this difference will be included in your ABV calculations when you take the FG reading.

While you can go through all that work to get a slightly more accurate measure of the alcohol in your beer, the main point of this whole rant is that the change in alcohol due to the addition of fruit is small enough that you can comfortably ignore it. Although you might want to pay attention if you are adding fruit to a base beer that is exceptionally strong or weak, or using a large amount of a fruit that has a substantially different gravity than the beer it is being added to.

Sorry about all the math, just a bit of the Mad Economist sneaking out...

This...is probably the best piece of brewing information I've read in a very long time. Now I have an effective way to determine the gravity contribution of fruit to my fermentations (not just beer, this also applies to mead). Thanks, Mike!

ReplyDeleteWhile we're on this topic, what would be an accurate way of determining the impact of fruit juice on a beer? I have an all-grain apple brown ale recipe that is 20% apple cider (added to the wort after chilling), and I'm not entirely sure my method of determining its gravity contribution is accurate. Some time back, another homebrewer advised me on how to convert 1.034 OG apple juice to a pppg value (1.005 pppg) for use in ProMash. Using that method, a gallon of apple juice plus 4 gallons of wort works out to 1.071 OG (it's intended to be a high gravity ale). Do you think this is pretty accurate? Or could you suggest a better method?

That's the last time I'm ever adding fruit to a beer!

ReplyDeleteTaylor-Made, you can calculate it like this:

ReplyDeleteIf apple juice is 1.034 and you add one gallon, plus 4 gallons of wort at 1.0XX, then it's:

(1 x 34 + 4 x XX) divided by 5 = your O.G.

Right on. I think a lot of people assume that most of the fruit is solid and not liquid and will drop out and no longer account for any liquid volume. It's clearly not the case.

ReplyDeleteYes fruit has sugar but also has water. I doubt any of the commonly used software packages have another way of dealing with this other than something like the dilution tool that beersmith has.

Glad you guys enjoyed the post. As Sean said, if you are mixing two liquids the easiest way to figure out the effect is to take a weighted average of the gravities. Giving the liquid a PPPG works, but only if you adjust the total volume of the batch to account for the increased volume.

ReplyDeleteThanks for the rundown. I've thought about this before and come to pretty much the same conclusions, and I like to see you putting it out there on the internet.

ReplyDeleteThanks for the answers, guys!

ReplyDeletePromash also had a dilution feature you can use to recalculate your O.G. based on adding water or wort of a specific O.G. You could use that.

ReplyDeleteNever apologize for "the math"; math is the language of discrete precision, and allows you to convey meaning efficiently. It's part of the reason I read here. The quantification of brewing details is a nice addition to the organoleptic breakdowns so commonly found.

ReplyDeleteThanks Doug, glad my nerdish leanings are appreciated!

ReplyDeleteYou write a great blog. I hope you're doing well by it. I say this as both a homebrewer and a yeast biologist.

ReplyDeleteThanks for the info, Michael. I'm doing a saison dupont tribute, just racked it onto 10lbs of peaches(frozen\thawed) with the gravity at 1.0075(using wyeast 3711). I'm toying with doing a gallon or two with brett. Should I add that soon or wait til the peach sugars are digested? Love your book, have recommended it to multiple people. Thanks, and GO HAWKS ;)

ReplyDeleteIdeally you'd have pitched the Brett well before the peaches. The Brett will take time to contribute its character, but all that time the fruit flavor will be fading. I'd get the Brett in ASAP, and consider adding more peaches when they are back in season in a few months to boost the flavor if needed.

ReplyDeleteThanks for the advice, Michael! I'll probably just do Brett on the next batch I brew. I'm definitely inspired by Logsdon's work-their peche n' brett is fantastic. I need to re-read your book to imprint all that info more solidly! Cheers

ReplyDeleteThe premise in the rant is basically that you're mixing two alcohol-based liquids together (like mixing a first-runnings 1.070 wort with a second-runnings 1.025 wort). In these cases, it should be clear that the mixture would have to have something in between the two, skewed toward whichever one had the greater volume.

ReplyDeleteThat's clearly not what's happening when you add fruit to wort. The fruit doesn't go in the wort full of water and come out dried up like a raisin. When you add fruit to wort, you're adding water and sugar, yes, but then when you take the "spent" fruit out, you're removing about the same amount of water (maybe more, maybe less). Where's the sugar go? The little yeasty beasties had a feasty and belched out a bunch of alcohol! So, regardless of whether you start with a low or high gravity wort, adding fruit

willincrease the ABV of your beer. Seehttps://www.morebeer.com/articles/fruit_in_beerfor more details.The issue with your assertion (and that article) is that you are assuming that the liquid that comes out with the fruit is 100% water. This simply isn't the case. When you mix alcohol and water together they don't stratify like oil and water, they mix together. As anyone who makes brandied fruit will tell you, fruit will absorb alcohol from the mixture you soak it in. Adding whole fruit is no different than mixing fruit juice into beer, there isn't a layer of beer and a layer of non-alcoholic juice, the whole thing blends together into a homogeneous fruit-beer as the yeast ferment and simple diffusion occurs!

ReplyDeleteYour opening paragraph says "...if you're adding fruit to a strong beer it will actually lower the final alcohol content." Consider this...

ReplyDeleteUsing your example, I brew an imperial stout with a post-boil OG of 1.106 and a post-boil volume of 5 gal. Tastes good. Next time I brew that exact same beer, but this time decide to add fruit to it. Knowing the fruit I'm going to add contains a good amount of water (let's say a half gallon of water), I boil such that my post-boil volume is 4.5 gal. I add my 10 lbs of 14 P cherries, which, as you point out, is equivalent to adding 0.5 gal of 1.057 solution. My measured OG at this point is 1.113, about 7% higher. Strong beer, added fruit, stronger beer.

If I had started with a smaller (1.040) beer, adding the fruit under the same conditions would bring the OG to 1.047, an 18% increase. Small beer, added fruit, bigger beer.

BUT, you say, if you hadn't added the fruit, your imperial stout would have had an OG of 1.118, and soadding the fruit made the beer weaker.BUT,Isay, if I weren't going to add the fruit, I wouldn't have boiled it down to 4.5 gal.What I'm saying here is that you have clearly and unequivocally said that adding fruit has a negligible or detrimental effect on the alcohol content of the final beer. People are using your blog to support that position (kudos to that). The fact is, your statement has an implied condition in it that isn't understood by most of your readers. I'll accept your premise IF you restate it as:

Without taking the fruit's added water into account, adding fruit to a beer will have a negligible or detrimental effect on the beer's alcohol content. If the water content of the fruitistaken into account, then the added fruit can significantly affect the alcohol content, especially of smaller beers.Without that caveat, the argument could be made that adding LME to a wort will reduce the gravity of most worts since LME, like fruit, can be considered nothing but sugar water (weaker sugar water, in fact, than fruit).

You are essentially correct, but your addressing a different question than the one I set out to deal with. If you concentrate your wort and then add fruit to dilute it, the fruited wort/beer will be stronger than an equivalent batch with the same amount of malt-based fermentables and no fruit and the same target volume.

ReplyDeleteThis post is debunking the commonly held belief that adding fruit after the OG reading is taken will invariably increase the ABV above the level it would have been prior to fruit. All else being equal, in most cases the water contained in fruit will dilute the existing sugars/alcohol enough to offset the sugar it adds.

If you are adding the fruit before taking the OG reading, you can use the OG in a standard alcohol calculation without need to do any adjustments. If you adjust your recipe/process to account for the added water then fruit will add sugar and increase OG/ABV compared to diluting with pure water.

I do have to disagree on your LME example though, because LME is denser than wort and will invariably raise the ABV of any beer/wort that it is added to even without account for its water!

Do you do anything with the spent fruit? I'd like to something with it, but have no idea what. Seems a pity to just throw it out. I have 3.5# of raspberries. Thanks, cheers!

ReplyDeleteI used cherry juice concentrate in my brew (tough to get affordable cherries in Alaska), so nothing leftover. Try baking the raspberries in a bread or something? I'm making a sour with ~9 lbs of peaches, but after 9-12 months in conditioning, I'm not sure they'd be worth using in something else...

ReplyDeleteYou can age a second beer on the fruit if you want to give a light fruit flavor. I'll say though, that Jester King uses about that much fruit per gallon in Atrial Rubicite before transferring Vie en Rose onto the fruit (and the fruit is pretty subtle).

ReplyDeleteI agree with your calculations mathematically and logically and via lived experience in a commercial brewery. I also agree with all the comments that follow, including the debate about adding fruit post-boil to a deliberately more concentrated wort. However, I also agree with your critique that this tangent addresses a subtle variation of your original premise...which I also understood clearly.

ReplyDeleteIn summary, this is an excellent article with excellent comments and debate.

And never apologise for the maths - some of us are actually numerically capable and prefer the proof than just arm-waving assertions ;)