Ask The Experts: Oxygenating Wort, Fruit Beers, Dark Malts

Homebrew expert Brad Smith, author of the Beersmith brewing software and the voice behind the Beersmith podcast, tackles your homebrewing questions about oxygenating wort, brewing with fruit, and using dark crystal and other darker malts.

Brad Smith Sep 6, 2017 - 10 min read

Ask The Experts:  Oxygenating Wort, Fruit Beers, Dark Malts Primary Image

Do I really need to aerate/oxygenate my wort before pitching yeast when brewing? If so, what’s the best way to do it?

The short answer is “Yes, you need to aerate/oxygenate your wort.”

While homebrewers consider any oxygen in their finished beer a bad thing, oxygen is critical for proper reproduction of yeast cells during the “lag phase,” when they are just waking up. During this phase, the yeast cells are rapidly reproducing and need oxygen to grow. Unfortunately, the process of boiling your wort forces almost all the dissolved oxygen from it, leaving it oxygen-depleted.

So you need to add some oxygen back into the wort after boiling, but before pitching your yeast, to get a strong fermentation. By far the best way to do this is by using pure oxygen. In fact, one of my new favorite toys is an “oxygen wand,” which is a stainless-steel tube with a stainless aerator at one end. You attach the wand to a tube and a regulator that connects either to an oxygen tank or a disposable oxygen canister. For about $60, an oxygen wand can aerate your entire batch to the ideal 8−10 ppm oxygen content in about 60−90 seconds. I use it after transferring wort to the fermentor, just before I pitch my yeast. It works well with cider, mead, and wine, too.

A slightly less effective method is to use an aquarium air pump and aeration stone. You can find these at any department or pet store that carries fish/aquarium supplies. To use one, simply sanitize your aeration stone and tube, put them in the wort, and start the pump. It’s best if you also have an inline filter to avoid drawing ambient yeast/bacteria in with the air. Unfortunately, since air is only 21 percent oxygen, you won’t be able to quite reach the ideal 8−10 ppm oxygen level. It will also take some time—likely 20−40 minutes.


The third option is simply splashing the wort around both as you are siphoning and while in the fermentor. Shake, rattle, and roll the fermentor as much as you can to try to get oxygen into it. This works well with a bucket or carboy as long as you can temporarily seal it. It is not as effective as the previous two methods, but it is far better than doing nothing.

I tried my hand at making a strawberry beer with several pounds of strawberries in the fermentor, but why was there virtually no strawberry flavor in the finished beer?

Fruit beers are notoriously difficult to formulate and ferment properly. Several challenges need to be overcome to get a good fruit flavor in your beer. First, you need to understand that fruits are mostly sugar and water. The simple sugars in fruits rapidly ferment into alcohol, leaving you with none of the sweetness you might expect from a strawberry or cherry beer. Another challenge is that fruits added in the primary have much of their aroma and flavor scrubbed away as CO2 bubbles through the beer. So in addition to losing the sugars, you also lose most of the aroma. Fermented fruits won’t taste the same as unfermented ones. Finally, both the malts and the hops we use in beer tend to mask what little fruit aroma and flavor you have left in the beer. Some fruits simply don’t ferment out well. Strawberries, in particular, tend to ferment to dust (unless you use a ton of them), leaving almost no flavor in the finished beer. Certain fruits do stand up much better—raspberries, blackberries, apricots, black currants, apples, and even cherries tend to come through more in the finished beer. There are strategies you can use to counter the problems above. First, you can use fruit flavoring syrups. These are sold in a variety of flavors and should be added at bottling time, and you can even add them “to taste” to get the amount of flavor you like. The only downside is they tend to taste like syrup or soda pop instead of naturally fermented fruit.

Another strategy is to use “backsweetening.” In this method, you ferment out your beer completely and then add some sulfites and sorbates (used in wine making), which will inhibit further yeast growth. Add the sulfites first, about 12 hours before the sorbates, and then wait a few days to let the chemicals inhibit the yeast. After the yeast has been inhibited, you can add fresh fruit juice or even fruit to the beer, again “to taste” until you get the balance of beer and fruit you want. Your beer will taste more like fresh fruit than fermented, which could be good or bad depending on your goals. Please keg and don’t bottle your beer if you backsweeten because fermentation could start again, creating bottle bombs.

A third strategy is to “go light” with your beer recipe. A light wheat-beer base, for example, is a good starting point, because it has very low hops and malt flavors, which should let the fruit shine through. Adding fruit to the secondary can also help to reduce the loss of aromatics. Keep in mind that even with a light beer base, you need a lot of fresh fruit—generally 2−4 pounds per gallon (907 g−1.8 kg per 3.8 l) to get a strong fruit flavor in the finished beer.


There is a final lesser-known strategy that select mead/braggot makers use that can also be used in beer. This strategy is to “go big” with your recipe! It’s high risk, but when it works, it is fantastic. The basic idea here is to create a fruit/beer mix that has high enough alcohol content that the yeast cells actually peter out and can’t finish the fermentation. In this case, you create a high-gravity base recipe and select a yeast that has moderate tolerance for alcohol. You want the yeast to reach its alcohol tolerance level before it can consume all the sugar in the fruit, leaving some residual fruit sugars and flavors.

The idea is to create a high-gravity beer, ferment it to close to its alcohol limit in the primary, and then add fruit to the secondary, and the yeast will reach its alcohol limit. It is “high risk” because you need to carefully manage the yeast nutrients, alcohol, and pH levels, or you won’t get a complete fermentation, leaving you with some very sweet and malty tasting beer. This might work well for a big beer such as a raspberry imperial stout.

I’ve noticed that my beers using dark crystal malts and pale chocolate malt have a harshness to them—why is this?

In his most recent book, Mastering Homebrew, Randy Mosher notes that there is a “harsh zone” running from about 80L to 200L in color, where very few malts are produced. At the bottom of that range you have brown malt, which runs from roughly 40−60L, and at the other end is pale chocolate, which is roughly 200−240L. But no conventional malts are produced in the middle because malts in this range have a very sharp, harsh, bitter, nasty character.

No one would buy them. Even dark brown malt takes on many coffee overtones, and pale chocolate can also be sharp and harsh in large quantities.

However, when we look at dark crystal/caramel malts, there are several produced in this “harsh” range, including Crystal 80, Crystal 100, Crystal 120, and Special B. They are commonly used by extract and all-grain brewers to add some color to medium beers, often with poor results. Along with a bit of color come sharp, harsh, bitter, and burnt coffee−like overtones.

To counter this, you need to really limit the use of malts in the 60−200L range. In fact, you are better off adding a small amount of roast or chocolate malt to get coloring than adding a pound or two of Crystal 80 or 100. I personally try to keep these malts below 2 percent each for any light- to medium-colored beer and below 4 percent each, even in a darker beer.

This is not to say that malts in the “harsh zone” don’t have their uses. I made a porter recently with 3.5 percent Special B malt, and it added a nice raisin note to the beer without coming across too strongly. I enjoy using brown malt with its slight hint of coffee. Pale chocolate, which is sharper than regular chocolate malt, can be nice in a complex porter or stout. The key is that malts near the “harsh zone” need to be used sparingly in a targeted manner to accent their flavor and not just as a method to add color to a light beer.