This week we cover the technical topic of the diastatic power for mashing your all grain beer. While rarely covered, this topic is an important one, especially for home brewers making beers with high percentages of non-barley or specialty grains. This is an important topic for partial mash brewers as well, since they are often mashing with a high percentage of specialty grains.
The Malting Process
The story of diastatic power starts as part of the malting process. As we covered a few weeks ago in the article on Malting at Home, the malting process consists of placing raw barley grains in water and germinating (sprouting or growing) them until the acrospire (the little leaf growing inside the husk) reaches a length close to that of the grain itself. The malt is then kiln dried, and the tiny sproutlets fall off, leaving malted barley. For darker and specialty grains the malt is roasted at varying degrees of time and temperature to achieve everything from caramel malt to stout roast.
The purpose of the malting process is primarily to break down the protein structure of the hard grains and make them friable for mashing. In fact, you may often hear the term “modification” of the malt. Highly modified malt has almost all of its protein structure broken down, while undermodified malt still contains a significant portion of unfermentable proteins and complex starches. A secondary effect of malting, however, is to develop the enzymes (notably beta amylase) needed for mashing.
Diastatic power refers to the enzymatic power of the malt itself – its ability to break down starches into even simpler fermentable sugars during the mashing process. The term “diastatic” refers to “diastase” enzymes. There are two “diastese” enzymes, the first is alpha amylase and the second is beta amylase. These enzymes might be familiar to many of you who have been brewing all grain for a while, as they are the primary enzymes active when you mash your grains in the normal temperature range of 148-158F.
So why should an average homebrewer care? If you don’t have sufficient diastatic enzymes in your mash, you simply will not be able to properly convert sugars during the mash. This will leave you with a partially fermented very sweet beer, with very low alcohol content.
Diastatic Power is measured in degrees lintner (often denoted with a big °L), though in Europe a secondary measure of Windisch-Kolbach units (degrees °WK) is often used. You can convert from one to the other using Lintner=(WK+16)/3.5 or going the other way as WK=3.5*Lintner – 16. A malt needs a diastatic power of approximately 35 °L to be considered “self converting”. Some of the newest American 6-row malts can have a diastatic power as high as 160 °L. (Ref: Wikipedia)
You can get the lintner values for many common malts from the malt supplier’s specification sheet, or from our BeerSmith database. Lets look at sample lintner values for a few commonly used grains:
- American 2 Row Pale Malt: 140 °L
- American 6 Row Pale Malt: 160 °L
- British Pale Malts: 40-70 °L
- Maris Otter Pale Malt: 120 °L
- Belgian Pale Malt (2 row): 60 °L
- German Pilsner Malt: 110 °L
- Munich Malt (10 SRM): 70 °L
- Munich Malt (20 SRM): 25 °L
- Vienna Malt: 50 °L
- Wheat Malt, German: 60-90 °L
- Wheat, Unmalted (flaked, Torrified): 0 °L
- Crystal Malt (all): 0 °L
- Chocolate Malt: 0°L
- Black Patent Malts: 0 °L
A few things become obvious looking at the above examples. With the possible exception of the very lightest specialty base malts such as Vienna or Munich, few specialty malts provide very much enzymatic power. Almost all of the enzymes needed to convert your mash are contained in your base malt, so the selection of a good base malt is important. Wheat provides diastatic power nearly equal to barley so it can be used in large proportions to make wheat beer.
Diastatic Power for All Grain and Partial Mash Brewers
How does this affect your all grain brewing? Clearly if you are brewing an all grain batch with a high power base malt like American six row, you will have plenty of enzymes available to convert your mash, and it will also convert at a faster pace than it might otherwise. However, if you are using a low power 2-row British malt with a large number of specialty malts, the sugars will still convert but might take substantially longer to do so.
A few specific styles can also cause problems for the all grain brewer. Lets take the example of Belgian Wit, which typically is made from 60% pale malt and 40% unmalted wheat (often flaked or torrified). If you select a Belgian Pale Malt base malt with low diastatic power, you may be in for a very long mash as the unmalted wheat contributes no enzymes to the process. The grains will likely still convert (little of the unmalted wheat will convert in any case) but it may take a long time to reach full conversion.
Diastatic power plays an even more important role for partial mash brewers. Many beginning partial mash brewers tend to take several pounds of specialty malts and try to mash them without a pale base malt. This can cause very poor conversion, as the fermentable portion of the specialty malts lack the enzymes to convert. It is important that you mash with sufficient base malt to provide the enzymes needed in the mashing process.
Estimating Diastatic Power for your Mash
To get a quick idea of whether you have sufficient diastatic power in your all grain or partial mash brew, I recommend you simply average the weighted diastatic power of your ingredients and see whether the final number is greater than the 30 Lintner minimum needed to convert. The overall diastatic power for your mash would be the sum of the diastatic power for each ingredient times its weight divided by the total grain weight. To get this number, just multiply the diastatic power for each grain times the weight of that grain, add the numbers up for all of your grains, and divide by the total grain weight.
Lintner_for_batch = Σ(lintner_for_grain * weight_of_grain) / (total_batch_grain_weight)
Lets look at a quick example: a partial mash using 2 lb of Caramel Malt, 1 pound of chocolate malt, and 1 pound of British Pale malt, with a diastatic power of 50 Lintner. The Caramel and Chocolate malts both have a diastatic power of zero, so they each contribute (0L x 1lbs) and (0L x 2lbs) for a total contribution of zero lintner-pounds. The pale malt is (50L x 1 lb) for a total contribution of 50 L-lbs. Now we add the contributions for all three up (which is 0+0+50) or 50 L-lbs. Now we divide by the total grain weight in the mash which is simply 4 lbs, which leaves an overall average diastatic power of 50/4 or 12.5 Lintner. Since this number is smaller than 30 L needed to convert the overall mash, another few pounds of pale malt or a grain with higher diastatic power might be warranted.
I will note that the above calculation is a rough approximation, as the specialty grains are only partially fermentable and contain many non-convertible starches, but I usually prefer to err on the side of more enzymes rather than end up short in the mash. Also, I don’t like to wait forever for my mash to complete, so I will often shoot for a number higher than the 30 L limit shown above. Note that this calculation is really only needed for mashes with high percentages of specialty malts, as most modern base malts have very high diastatic power.
Don't make another bad batch of beer! Give BeerSmith a try - you'll brew your best beer ever.
Download a free 21 day trial of BeerSmith now