Regardless whether one believes that decoction mashing will add extra flavours to the brew,  it is certain that it will increase the mash efficiency in the region of 8%.  In order to achieve a full-bodied lager with the light colours that are characteristic for a Helles, the higher the mash efficiency, the better.

Here is how it can influence the colour of the beer in a typical grain bill.

Masch Schedule Mash Efficiency Brewhouse Efficiency Colour (EBC)
Hochkurz 55-62/72/75 72% 89.3% 6.4
Infusion 55-62/72/75 64% 79.2% 7.2

Not having access to a mash filter as well as the inability to mill the grain in such a way that it is possible to perform an endorsperm mash, a few EBC more should be added the to the resulting colour of the intended brew.

For e.g. a mash filter can easily propel the mash efficiency in the 85% range, which will send the brewhouse efficiency towards an impossible 105%! So much about brewhouse efficiency as yardstick… To break it down a little, a spelt masch (or endosperm mash) can reduce the colour by about 0.8 – 0.9 EBC, whereas the increased brewhouse efficiency due to the better sparge extract yields of the mash filter can easily contribute another 0.4 – 0.6 EBC in colour.

I generally calculate my grain bill at the slightly darker end of the scale for precisely these reasons. Although I do happily mash my lagers via decoctions, I don’t have access to a mash filter or a 6 roller mill… I simply add 1.2 – 1.5 EBC to my calculations in the final grain bill.