For malt extract:
BJCP Description of Witbier characteristic ingredients: "Unmalted wheat (30-60%), the remainder low color barley malt. Some versions use up to 5-10% raw oats or other unmalted cereal grains. Traditionally uses coriander seed and dried Curaçao orange peel. Other secret spices are rumored to be used in some versions, as are sweet orange peels. Mild fruity-spicy Belgian ale yeast."
Continental pilsner malt should be the base. Unmalted wheat or flaked wheat should be about 1/4 of the grist. If malted wheat is used, beer-analytics.com suggests higher amounts, such as 29 to 47%. Oats can range from 5 to 10%. Small amounts of Munich malt (3 to 5%) are optional.
Wheat and oats can be gummy, raising the risk of a stuck sparge. Consider using rice hulls for more husk matter and a slow sparge rate. Step mashes and cereal mashes are also strategies for dificult mashes. Flaked wheat and flaked oats, in contrast, can simply be added to the mash.
The source recipes suggest about 45 to 50% unmalted wheat, but the beer-analytics.com analyses suggest a lower amount (25%). However, the malted wheat proportion from beer-analytics.com is about 50%.
Creative brewers who want to push the style boundaries can try other grains (rye, rice, millet, buckwheat) and spices (cumin, lemon grass, rose hips, heather tips, grains of paradise, cardamom, and hibiscus). Hotter spices (pepper, ginger, etc.) in small amounts could also be explored.
The recommended hops are the standard noble European hops, such as Saaz, Hallertau, Tettnanger, and Hersbrucker. Similar hops might be substituted. Most recipes call for a single bittering dose. A BU/GU target ratio is .3.
Possible late boil spices are citrus zest, coriander, and chamomile. Use restraint. The suggested doses are from Zainasheff's Blanch Oreiller recipe: 2.25 g/l of fresh citrus zest, .6 g/l crushed coriander, and .05 g/l dried chamomile flowers. These are added five minutes before the end of the boil.
Mosher (2004, p. 206) describes orange peel as a "universal" spice for this style. He prefers fresh orange peel zest over curacao - bitter orange peel. In particular, he prefers Seville oranges. He also recommends coriander from Indian grocery stores over the standard grocery store coriander. The third recommended spice is chamomile.
There are several style-specific yeasts, such as Wyeast 3944, White Labs WLP400, and Mangrove Jack M21 (dry). Other Belgian yeasts might also work.
Beer-analytics.com witbier analysis
Burnsed, J. (2011, July-August). Witbier: The style that got a second chance. Brew Your Own, 36 - 43.
Klemp, K.F. (2012, May). Belgian witbier. All About Beer, 33 (2), 80 - 81.
Mosher, R. (2004). Radical brewing: Recipes, tales, and world-altering meditations in a glass. Brewers Publications
Strong, G. (2021, March-April). Witbier: A hazy shade of summer. Brew Your Own, 24 - 28.
Zainasheff, J. (2007, July-August). Witbier: The cloudy beer with the silver lining. Brew Your Own, 19 - 22.