Diastatic Power in malt
What is the lowest DP a malt can have and still convert itself in a typical, single step infusion mash without problems? I know some well-modifed British malts can be as low as 40 and still convert by itself, but what's the lowest? The second question is, theoretically, could a malt with a DP of 1 convert itself if given an unlimited amount of time? I'm sure in that unlimited amount of time a whole bunch of things could go wrong, but I'm just wondering about conversion.
Diastatic Power in Malt
The answer to your question is that for the most part, "it depends". Enzymatic systems are very complex and as such have a number of variables that affect the outcome of their actions. This really is more off a theoretical question which is taken into consideration in this answer:
Enzymes are catalysts so one would think that a DP of 1.0 would just mean the reaction would be slower than a DP of 101.0? This is not necessarily the case since starch conversions with enzymes, as mentioned, are very dependent on a host of factors.
The DP measured in malt is considered a measure of the
total enzymatic power of the malt. There are more enzymes in malt than just alpha and beta amylase. As these enzymes convert starches to fermentable and non-fermentable sugars through a spectrum of temperature changes, (ie: The Mashing Cycle), the pH also changes which in turn alters the ability of other enzymes to react. The three main control factors in Mashing are Time, Temperature and pH, (and to some degree one could argue Alkalinity).
Another factor that contributes to an enzyme's effectiveness in a mash is the water to grist ratio. This can affect the enzyme's ability to promote the reaction.
The answer whether a DP of 1.0 would work or not is "No".
From a theoretical standpoint the scientist might say it should....
but... if you leave a mash at conversion temperature the pH begins to drop due to formation of lactic and other acids... The more the pH drops the less effective the enzyme becomes and eventually will be completely inactivated in a low pH environment before the mash is completely converted.
DP is a tool for the Brewer to convert his starches. Whether they are malt starches or adjunct starches the level of enzyme should be determined by the the Brewer to reach the goal for her/his final Wort Composition. Therefore there is no right answer to what is the lowest DP a Brewer could use because "It Depends". It depends on the composition of the mashing water, the time, temperature and pH of the mashing cycle. But above all it depends on the final Goal of the Brewer for her/his final Wort Composition given the beer style and raw materials the Brewer intends for the final product.
If you have any question as to whether a particular malt will have conversion problems due to low DP, simply discuss this with your supplier. They should be able to tell you whether it will convert itself, or itself and perhaps some low (or zero) enzyme starch sources like high color malts or adjuncts.
Could you please explain grist ratio
I thought your post was very intriguing considering that I don't even use diastatic power. I have many questions, but mostly, I am wondering about the malt to grist ratio. Could you explain what happens to enzymes when the ratio is lower and when it is higher? For example what would the difference be between a ratio of 1.5 lbs of grain vs. 1.3 lbs of grain.