Ask Mr. Wizard

Protein rests when brewing with wheat


Richard Bray • Omaha, Nebraska asks,

I would like to know if I should do a protein rest for grain bills with over 25% wheat. I have heard conflicting advice and cannot seem to get a clear answer either way.


This is a great question, Richard. The short answer is no, you do not need to do a protein rest when brewing with more than 25% wheat. However, many brewers want to use a protein rest for several reasons. To give this question a proper discussion I will briefly differentiate raw wheat from malted wheat, touch on what “the protein rest” means to the practical brewer, and finish with why brewers may choose to use this rest when brewing wheat beers.

When it comes to brewing with wheat, there are four main types: Raw wheat, flaked wheat, torrefied wheat, and malted wheat. Raw wheat is what comes out of the field when wheat is harvested and threshed to separate the wheat berry from the husk and stem. Flaked wheat is produced by steaming then smashing wheat berries into flat bits, whereas torrefied (or torrified) wheat is produced by using radiant energy to intensely heat and puff wheat berries. Both processes partially gelatinize wheat starch. Torrefied wheat has more flavor than flaked wheat and can also be flaked after torrefication, making it difficult to know which flakes are steam-rolled and which are torrefied. Malted wheat is hydrated through steeping, germinated, and kilned like other malted grains.

The primary differences between the three unmalted wheat types and malted wheat, is that the unmalted types contain undegraded cell wall material, lack alpha amylase and other enzymes developed during germination, and are exposed to minimal heat during processing. In practical terms this means that the unmalted types may lead to difficult wort separation due to beta-glucans, will dilute malt enzymes in the mash, and dilute “malty” flavors associated with malted grains. And because wheat usually contains more protein by weight than barley, unmalted and malted wheat types contribute more protein to wort than malted barley. It’s also important to recognize that wheat, unlike barley, loses its husk when “combined” or harvested.

Let’s take a break from stating facts and look at the protein rest using more specific terms. The protein rest is used to reference mash temperatures in the 113–131 °F (45–55 °C) range. Originally named for the increase in amino acids measured after mashing in this temperature range, the protein rest is not just about protease activity. Lipoxygenase, beta-glucanase, arabinoxylanase, and ferulic acid esterase are other enzymes active at these cooler mash temperatures. Depending on a brewer’s intent for using a low temperature rest, different names may be used to describe the same rest.

Using unmalted grain and want to avoid headaches associated with beta-glucans? Consider using a “beta-glucanase rest.” Want to boost the clove-like aroma of your summer hefeweizen? Extend that “ferulic acid rest.” Or are you looking to boost the amino acid content of your rice lager wort? Time to drop in a “protein rest.” But if you are brewing with lightly kilned malt, beware of lipoxygenase activity at lower mash temperatures because it can lead to the development of wet paper aromas from the formation of trans-2-nonenal (now E-2-nonenal because of changes in stereochemical nomenclature).

Now it’s time to dig into your question. Should you use a protein rest when using wheat? The official answer has changed; it’s now “it depends.” First, why are you using wheat in your beer? And are you using unmalted wheat or malted wheat?

Let’s assume you are using unmalted wheat because it’s great for beer foam, is relatively easy to use, adds a nice snap to lighter-colored beers, like wit, and is a good source of protein for the hazy beers. These goals can all be achieved without the protein rest. However, you may run into an issue with wort separation because unmalted wheat contains undegraded cell walls that are rich in beta-glucans. Adding a rest around 113 °F (45 °C) may be something to consider because this temperature is ideal for beta-glucanase activity. You will also have other enzymes active at this temperature and need to be aware of what they may do for your brew. If you are looking to reduce wort viscosity and improve run-off and yield, the pros are likely to outweigh the cons.

Using the same basic example, consider a problem where extract yield is low when using 40% unmalted wheat and a single temperature mash. One explanation is that the beta-glucans and high-molecular proteins that bind starch granules into the matrix of the endosperm need to be digested. We’re back to another benefit of using a low-temperature rest in the 113–131 °F (45–55 °C) range. But low yield also occurs with poor conversion, i.e., failure of the iodine test to show a negative reaction. Incomplete conversion can be caused by enzyme dilution, and adding a protein rest won’t fix that.

I am a big fan of hefeweizen and will finish this discussion with an example using malted wheat instead of unmalted wheat because German brewers only use malt. If we want to give plenty of ferulic acid for weizen yeast to convert into 4-vinyl-guiacol, the best thing to do is mash in where ferulic acid esterase can do its thing by freeing up ferulic acid from arabinoxylans. Again, we are back in the same temperature range. Adding a 30-minute rest at 113 °F (45 °C) is a technique used by weizen brewers to boost clove notes.

Some brewing questions lack clear answers because there is no single way to tackle the problem. But when it comes to questions about the protein rest, things become murky because the term we use to describe rests in the 113–131 °F (45–55 °C) range are not about a single topic. With that, Richard, it’s time to brew with wheat!

Response by Ashton Lewis.