Where does this DME/LME come from in "How to Brew"?

Question

I have a copy of the last (4th) edition of "How to Brew" by John Palmer.

According to the book, DME yields 42 PPG (Points per Pound per Gallon), while LME yields 36 PPG. This is an estimation since the exact numbers depend on the extract. As a consequence:

LME = (42/36) * DME = 1.1667 * DME

This is not far from what is stated in the most voted answer here on this topic. The starting PPG estimation there is different so it all makes sense.

Later in the book, in his Porter recipe, Palmer says to either use 6 lbs of DME or 7.6 lbs of LME, but 1.1667 * 6 = 7.

Though it isn't a big difference, I'm trying to understand how these things work: is there something more that must be taken into account, am I missing something or it's just a typo?

Answer 1

LME already has some liquid in it. Making the yield slightly less than DME per volume but much more exaggerated when measured by weight.

While maltsters do thier best for consistency yields will vary between batches and maltsters.

So you really can't have any accurate static value of yield for LME / DME or even All Grain.

Maltsters have data sheets for all of thier products. Recipes should be adjusted accordingly. A well recorded original recipe will include malt yields, AA % etc. Recipies are then adjusted at brewing for duplication and consitancy of a beer. Most issues are corrected by correcting OG.

Answer: The static ratio is an average and guess at best.

Palmer uses 1.25/1 ratio which is a ratio used by most. IE 6 lb DME = 7.5-7.6lb LME