[S. cerevisiae]

Limit dextrinase doesn't have a huge effect on the mash at the temps most of us use. It's peak activity is between 140-145F, and drops off rapidly at higher temps. It could have some impact during a long, low-temp mash for something like a light lager (which is probably why it appears in the literature), or if you're doing a low-temp mash for something like a big barleywine or belgian.

I found a paper written by Charlie Bamforth that sheds new light on limit dextrinase at lunch.  I am going to  read the paper this evening and attempt to distill it down to something that one does not need a Ph.D. in biochemistry to understand.  That's the problem with most brewing science-related papers.  We are not the intended audience. 

[narcout]

What I think is interesting about the paper I linked to above are the differences in both optimum temperature and heat stability between purified LD and LD as found in a malt extract. 

Also the LD in the malt extract was active at temperatures higher than what I had previously heard.

Edit:

I found a paper written by Charlie Bamforth that sheds new light on limit dextrinase at lunch.

Do you mind posting the link or the title?

[S. cerevisiae]

The paper is entitled "Barley and Malt Starch in Brewing: A General Review" (http://writing.ucdavis.edu/sciencewriters/pdf/bamforth/Bamforth_Review_Barley_and_Malt_Starch.pdf).  It covers more than limit dextrinase.


“Stenholm and Home (46) showed that a key factor is the 
state of purity of the enzyme. Thus, when purified limit dextri
nase is heated, it loses all its activity in less than 10 min at
 65°C. However, if crude extracts of malt are heated so as to 
mimic mashing, then in fact, some 60% of the activity is still
 present after an hour at conversion temperatures (Fig. 11). In
 this respect, it may even be more inherently stable in mashing 
than is b-amylase (32). 
 
Research in several laboratories has shown that the key issue is not so much heat sensitivity (which was the message from received wisdom) as the extent to which limit dextrinase is available in the mash. It is now recognized that the enzyme is bound up with other components of the barley grain and is not active. Anything that increases the extractability of the total bound limit dextrinase, together with factors that promote the release of the enzyme from its inhibition by the binding agent, will promote free limit dextrinase and, therefore, increase fermentability. This is, of course, necessary in the production of light beers (the biggest growth sector worldwide); but also, high levels of dextrins in beer can lead to gel formation and difficulties with filtration, so the availability of limit dextrinase has implications beyond securing fermentability alone.”

 
Some more food for thought

“Of perhaps more commercial promise for increasing limit dextrinase is a change of pH. Stenholm and Home (46) showed that limit dextrinase activity is substantially increased by lowering the mashing pH (Fig. 13). They clearly showed that there was a much greater correlation between free limit dextrinase activity and fermentability than there was with total limit dextrinase. In turn, fermentability correlated rather less well with a- and b-amylase. Osman (38) showed that the pH optimum for b-amylase (pH 5.5) is significantly higher than it is for limit dextrinase (pH 5) (Fig. 14). However, there is still substantial b-amylase activity at the lower pH. Certainly, it appears from the work from Home’s lab (46) that a potent tool for enhancing fermentability is to lower the pH of mashes.”

Here is the part of the paper that I found illuminating because all-grain home brewers rely on the iodine test to check on the state of conversion:

"The other molecule that amylose can bind when in aqueous solution is polyiodide (iodine), yielding the familiar dark blue complex. Amylose can bind up to 20% of its weight as iodine; however, bound lipid interferes. How significant is this when the brewer tests for conversion by using the simple iodine test? Might a residuum of unconverted starch be undetected? Furthermore, it is often overlooked that the major proportion of starch molecules, namely the amylopectin, binds less than 1% of its weight as polyiodide and yields a dull brownish color and not a blue one. To me, at least, it seems that the iodine test is severely flawed. However, equally, I am unable to offer a better suggestion for a procedure that is rapid and reliable."

I have treated that dull brownish color as dextrin since I started brewing all-grain beer.

[narcout]

Figure 13 was the most interesting to me as it showed that LD is still active at higher mash pHs.  I also think figure 14 is pretty useful.

I never saw the point of performing an iodine conversion test.

[erockrph]

Some thoughts I had as I read through this article:

A) It's impossible to read this without hearing it narrated in Charlie's voice. Especially when he uses the phrase "dead in the water".

B) How steep is the dropoff in limit dextrinase activity beyond 65C? Obviously this research is largely targeted at light lager breweries, but it would be nice to see another data point or two above 65C.

C) There are a lot of unanswered questions for me still. I'm not jumping to the conclusion yet that any of this data will translate to a more fermentable wort, at least for the beers I typically brew.

There are two assertions here that really seem (to me) like there is a high probability of cancelling one another out to some extent. The first is that free LD is rapidly degraded at higher temps, while malt extracts seem to preserve LD activity. The second is that a considerable portion of LD is bound in the malt and inactive. When I connect the dots, I come to a possible conclusion that the reason LD activity remains over an extended time in malt is because it is bound. By liberating more free LD, you would potentially see a more rapid degradation if it is only "protected" by being bound within the malt. Unless you can liberate LD at a faster rate than it degrades, you may not really get so much bang for your buck.

It seems like malt enzyme content and possibly temperature would play a large factor here. A more highly kilned malt mashed in the 150's may not see much of a benefit in fermentability by lowering mash pH. But at very low mash temps with lightly kilned malt, there seems to be a very likely benefit of targeting a lower mash pH to maximize free Limit Dextrinase in the mash.

[ynotbrusum]

Very interesting discussion and much of it beyond my ken, but will mashing longer at the lower end of the temperature spectrum with a relatively low pH optimize conversion for light lagers (as conventionally thought) or is there too much else to consider in the process to make this generalization?

[Wort-H.O.G.]

Very interesting discussion and much of it beyond my ken, but will mashing longer at the lower end of the temperature spectrum with a relatively low pH optimize conversion for light lagers (as conventionally thought) or is there too much else to consider in the process to make this generalization?

Presume you didn't mean me with "my ken"


Sent from my iPad using Tapatalk

[JT]

Best hour I've spent this week: http://media.libsyn.com/media/basicbrewing/bbr03-17-11kaiph01.mp3
From March 17th, 2011.  Kai Troester talks about pH measuring equipment, mash pH at room and mash temp, alpha and beta amylase, hop utilization, boil pH and fermentation pH.  Also covered: why batch sparging rules.  All on the drive to work!

[erockrph]

Very interesting discussion and much of it beyond my ken, but will mashing longer at the lower end of the temperature spectrum with a relatively low pH optimize conversion for light lagers (as conventionally thought) or is there too much else to consider in the process to make this generalization?

I don't think anything here is refuting that idea. The question regarding limit dextrinase has always been how much of a factor does it play in the mash. Conventional brewing wisdom has typically held that it degrades too rapidly at mash temps to have much of an impact. Charlie's paper proposes that limit dextrinase may actually be a bit more stable at mash temps than originally thought, and that a lower pH may increase its activity.

Limit dextrinase, for those who aren't familiar, is capable of breaking down bonds in starches that alpha- and beta-amylase cannot (it breaks alpha 1-6 bonds at branch points). The issue is that limit dextrinase cannot access these bonds until the amylase enzymes have exposed them first. Since your typical mash rest is at a higher temp than limit dextrinase's peak activity, it isn't believed to have much of an effect on fermentability. If you can somehow boost limit dextrinase's activity while the amylase enzymes are also active, then you could see a boost in fermentability.

I have accomplished this myself in a high-gravity barleywine. I did an iterated mash, where I held a high beta-amylase rest initially, then pulled my grain bag and added more grains to bring my mash temp down to the mid 140's. The idea was that the second grain addition would supply fresh limit dextrinase to break down the dextrins from the first mash. While it is only one data point, I was able to get 83% attenuation on a 1.142 wort using a flocculant English ale strain fermented at 58F. I was quite happy with my results.

[morticaixavier]

Very interesting discussion and much of it beyond my ken, but will mashing longer at the lower end of the temperature spectrum with a relatively low pH optimize conversion for light lagers (as conventionally thought) or is there too much else to consider in the process to make this generalization?

I don't think anything here is refuting that idea. The question regarding limit dextrinase has always been how much of a factor does it play in the mash. Conventional brewing wisdom has typically held that it degrades too rapidly at mash temps to have much of an impact. Charlie's paper proposes that limit dextrinase may actually be a bit more stable at mash temps than originally thought, and that a lower pH may increase its activity.

Limit dextrinase, for those who aren't familiar, is capable of breaking down bonds in starches that alpha- and beta-amylase cannot (it breaks alpha 1-6 bonds at branch points). The issue is that limit dextrinase cannot access these bonds until the amylase enzymes have exposed them first. Since your typical mash rest is at a higher temp than limit dextrinase's peak activity, it isn't believed to have much of an effect on fermentability. If you can somehow boost limit dextrinase's activity while the amylase enzymes are also active, then you could see a boost in fermentability.

I have accomplished this myself in a high-gravity barleywine. I did an iterated mash, where I held a high beta-amylase rest initially, then pulled my grain bag and added more grains to bring my mash temp down to the mid 140's. The idea was that the second grain addition would supply fresh limit dextrinase to break down the dextrins from the first mash. While it is only one data point, I was able to get 83% attenuation on a 1.142 wort using a flocculant English ale strain fermented at 58F. I was quite happy with my results.

that's interesting Eric. I too have managed to get extremely high AA%s in big beers that I mashed in the mid 140s straight through and fermented with english yeasts. I didn't think of LD as a culprit but it could well have been. I didn't add more grain though, I just mashed in at that temp and let it ride.

[erockrph]

that's interesting Eric. I too have managed to get extremely high AA%s in big beers that I mashed in the mid 140s straight through and fermented with english yeasts. I didn't think of LD as a culprit but it could well have been. I didn't add more grain though, I just mashed in at that temp and let it ride.

You will still get amylase activity at those temps, although a lot slower than at higher mash temps. So you don't necessarily need to add more grain as long as you hold the mash rest long enough. I was specifically trying to target limit dextrinase in that beer, as well as do an alpha rest before a beta rest, so that's why I went with the 2-step mash.

[Wort-H.O.G.]

Is it just me or is anyone else managing mash PH by room temp, and it varies by recipe? Perhaps I'm just wasting time and energy and a consistent mash PH of 5.5-5.6 Room temp is the way to go??? If I wanted a more acidic wort In the kettle I'd just adjust down- and that would carry through with the hops and yeast PH drop that happens........not feeling like there's much in responses suggesting a best practice here.

It's an area ripe for experimentation.

I do like to get my German Pilsners in the %.2-5.3 range so they really "pop". Dark beers up around 5.5-5.6.

I completely agree Jeff. mashing my German Pils as we speak...152F and PH came in at 5.25 - perfect. bittering with 1oz perle, then 1oz of spalt last 60min and 1oz last 20 minutes. 38IBU.

[HoosierBrew]

Another +1 for mashing pale lagers @ 5.2-5.3 - I like the crisp character I get at that pH.  Like Ken, I often split the difference and target 5.25.

[ynotbrusum]

Hey Ken, I was using "ken" as in the old usage of "limit of what I can know".  I think it is of Scottish derivation.  I enjoy the discussion in any event, even though I am just "kinda" getting the gist.

[Wort-H.O.G.]

Hey Ken, I was using "ken" as in the old usage of "limit of what I can know".  I think it is of Scottish derivation.  I enjoy the discussion in any event, even though I am just "kinda" getting the gist.

ha! wasnt sure if it meant to read "thinking" vs "ken". no worries.