Determining the Sugar Contribution of Fruit in Beer

By Gary Spedding (Brewing Techniques Magazine)

Your fruit adds more than just flavor to your beer.

I recently learned a valuable lesson about brewing with fruit. I found that the original gravity of a cherry wheat beer I had made was much higher than I had anticipated. It then dawned upon me that I had forgotten to account for the recovery of the sugars from the cherries themselves, which I had steeped in the hot wort for 30 minutes at the end of the hop boil. I knew that fruits can add fermentable sugar to the beer, but hadn’t realized how much.

If you are using significant volumes of fruit, it makes sense that you should factor it into the brewing calcs. But nowhere in the brewing literature have I seen any guidelines given for the brewer to figure out how much sugar is potentially available from fruit, an increasingly popular brewing ingredient. You could come up with your own figures by using a Brix hydrometer, but it would take some time. This article provides a little more information about the types of fermentable sugars and the amounts typically present in fruits used in the production of popular fruit beers.

Types of Sugar

The predominant sugars in most fruits are sucrose and the simple unit monosaccharides, glucose (dextrose) and fructose (levulose). All these sugars are readily fermentable by brewer’s yeast, and we can treat them all as “corn sugar” for brewing calculation purposes.

The accompanying table provides the typical content of each type of sugar in several commonly used brewing fruits. This table is adapted from the Foods and Nutrition Encyclopedia. For those who want to brew with more exotic adjuncts, the Encyclopedia also provides sugar contents for many other fruits and vegetables.

For all fruits except cherries, pit (seed) weight is included when appropriate. (For unpitted cherries, subtract 10% of the fruit weight to account for pits.)

The overall degree of ripeness of fruit influences total sugar content; riper fruits have a higher fermentable sugar content. Dried fruits also possess a higher sugar content, as illustrated by comparing the value for dates (almost 50% sugar by weight!) with that of the other fruits listed. If you use fruit puree, assume that you are adding about 20% more usable fruit by weight than if you were using whole fruit. If you use packaged fruit products, check the label for the sugar (not total carbohydrate) content.

Calculating Extract Yield

Here is an example of the calculations you’ll need to make to determine the sugar contribution of sweet cherries to your brew. In the table we find that their sugar content is 12% (or 0.12 lb of sugar per pound of fruit). Next, we determine the number of gravity units the cherries contribute by multiplying this percentage by the gravity contribution of 1 lb of corn sugar/gallon of wort. The fermentable extract potential of corn sugar in pounds per gallon is 1.037, which can be expressed as 37 GU. The calculation is therefore as follows:

0.12 lb sugar x 37 GU = 4.44 GU/lb of cherry fruit/gallon of wort

All of the corn sugar is fermentable because 100% of it is available in solution. In the case of fruit, the sugar must be obtained from the fruit pulp, so you will need to determine the efficiency of sugar recovery. I suggest, as a first approximation, that if the fruit is steeped in hot wort you will recover about the same percentage of sugar as you recover from the grain during mashing. If you already know your brewing efficiency, then the difference in gravity between your expected (calculated) or realized values based upon your grain bill and the gravity obtained after addition and steeping of fruit should enable you to simply back-calculate for efficiency of sugar recovery from fruit. Extraction efficiency may be different if you add fruit directly to the fermentor rather than to the hot wort, and it may also vary from fruit to fruit. Freezing would probably also have some effect. You may need to experiment a little to determine what happens in your system.

For a homebrew-scale batch (6 gallons) of a cherry wheat beer using sweet cherries, I estimated that steeping would recover 75% of the fruit’s sugar with the steeping method. (Note that this is for one preliminary experiment only. The fruit was frozen, then thawed prior to the steep.) So to obtain the actual recovery of sugar from my sweet cherries, I take total potential gravity contribution from the previous calculation (4.44 GU) aand multiply by the percentage I expect to recover (75%):

4.44 GU (100% yield) x 0.75 = 3.33 GU/lb of cherry fruit/gallon of wort

The fruit (6 lb total) thus contributed 0.54 lb of recovered sugar (0.12 x 6 x 0.75), or almost 20 GU (about 1 °Plato) to the 6-gallon batch. As you can see, this is a nontrivial contribution to the fermentables in the brew.

I hope that this information provides a useful starting point for the brewer of fruit beers. It should aid in formulating recipes and in precisely determining the alcohol content.

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