As the season changes from frigid temperatures and snow flurries to the blooming flowers and sunny days of spring my thoughts swing from heavy barley wines to the refreshing thirst quencher German style Hefeweizen. This is one of my favorite styles to brew and enjoy all summer long. The variations you see from batch to batch have a lot to do with not only the type of yeast you use but also the way you treat it during fermentation. Varying certain aspects of fermentation will produce varying amounts of the characteristic esters of banana and phenolic clove (spice) flavors and aromas in the beer. The main things you should take into consideration when fermenting German wheat beers are fermentor design, yeast pitch rate, level of aeration and fermentation temperature.
Most traditional German wheat beer breweries used a large shallow open fermentation vessel which promotes the production of both the banana and clove (phenol) character. On a homebrew scale a plastic bucket, either a 6.5 gallon or the 7.9 gallon, used without the lid can emulate the traditional vessel. When using a 6 gallon carboy with standard bung and airlock will produce moderate amounts of banana and high amounts of spice. Conical fermenters will produce low banana and low spice character. The taller and narrower the fermentor gets the lower the ester and phenol production.
The amount of yeast you pitch along with the amount of aeration you use work together to regulate Weizen characteristics. When using a high yeast pitch count and high level of oxygen you will experience low levels of banana, fruit and spice. If you maintain the high yeast pitch rare but reduce the oxygen level you will see moderate fruit and banana production along with low spice character. If you intentionally stress the yeast and under pitch but add higher levels of oxygen the fruit level will increase but the banana will remain low and the spice will be moderate. Finally if you use low levels of yeast and oxygen you will get high fruit and banana and moderate spice.
As with most any beer yeast the fermentation temperature is also critical in controlling the final outcome of the beer. Generally lower fermentation temperatures will produce a cleaner beer with lower ester and phenol production. As you increase the temperature you will see an increase in both banana and spice production but will see a decrease the other fruity esters as the temperature reaches and exceeds 72F. Fermentation temps can range for 60-75F and will vary based on the strain you choose.
There are a number of strains to choose from in liquid form and even a few dry options. The most used strain is the original from Weienstephan which is Wyeast 3068 or White Labs WLP300. This strain is the most responsive and is relatively easy to handle. Others that I would recommend would be the White Labs WLP380 Hefeweizen IV which has lower banana production and Wyeast 3638 that produces more fruit esters and a unique banana character. Fermentis Safebrew WB-06 Dry Wheat Beer Yeast and Danstar Munich German Wheat Beer Yeast are the dry options available.