Enzyme activity vs. yeast/bacterial activity vs temparature
I was reading Whole Grain Breads by Peter Reinhart, and he explains at length on the benefits of delayed fermentation he learned from Philippe Gosselin. The summary is that Gosselin mixes cold water and flour, refrigerates overnight, and then mixes the dough the next day. PR says that he approximated the method by mixing yeast+flour+water and then refrigerating immediately. The interesting claim here: PR says the extra flavor in the Gosselin method is due to enzyme activity releasing sugars into the dough, and his method does the same. This makes me ask: when you refrigrerate *with* yeast as PR advocates, both enzyme activity and yeast activity is slowed down. Then why is this a good approximate of the Gosselin method, which clearly gives a headstart (however small because of refrigeration) to enzymes? The PR explanation and the method don't seem consistent, unless it is the case that yeast activity is slowed down much more under lower temps than enzyme activity.
Second, PR advocates a hot or cold soaker made of whole wheat flour in most of the recipes. He advocates adding salt to the cold soaker to control enzyme activity so that dough doesn't get destroyed, which seems to make sense. But when making a mash (or hot soaker) of whole wheat flour, he omits the salt. In addition, he keeps the temperature around 160F to maximize amylase activity and suggests a 3 hour "holding period" at that temp to release sugars. (I tried that, it does release sugars and the hot soaker becomes quite sweet after about 3 hours). Now that soaker should have a LOT more enzyme activity than the cold wholewheat soaker to which we add salt. These two methods seem to conflict with each other as well. Can someone please explain this? (BTW, in both hot/cold soaker methods, the rest of the recipe seems approximately same too, so I don't think I overlooked some important enzyme-compensation process in the recipes).
I'm very curious to find the outcome of your question... good point there!
Happy baking!
LeeYong
I am sure Peter Reinhart would welcome your questions and a chance to clarify the topic. He can be reached via e-mail at
Peter.Reinhart@jwu.edu
These are interesting questions and I am sure we will all learn from the answers.
Ben
venkitac - If my understanding of the effects of temperature on yeast and amalyse activity are correct, then you've answered you first question: lower temperatures will slow down the activity of the yeast more markedly than that of the amalyse enzyme. The result will be greater production of sugar without a corresponding greater consumption by the yeast. Hence the wonderful flavor and crust coloration of Gosselin's baguettes.
As for the second, I'm stumped. Hamelman recommends salting both hot and cold soakers to inhibit too much amalyse activity, but for reasons of avoiding 'off' flavors that may develop rather than 'destruction' of the dough once the soaker is added.
Larry
I think the salt is added to the cold soaker not to slow the Amylase enzyme, but to prevent/slow other nastier cultures from developing. It may not be necessary for the heated soakers/mash because the heat itself may be outside the tolerable range for the nasty beasties to survive in.
rather than amylase?
Venkitac, I'm just guessing: just like amylase even protease will probably have a disactivation temperature. Maybe the hot water will take the temperature of the dough above the point of no return for protease? dunno, i'm just shooting in the dark.
Hi Nico,
You may be shooting in the dark, but your night vision is obviously pretty attuned!
The optimum temperature for the mash is 60-66*C. Safe hot holding temperature in the UK for food is 63*C, so that matches up with seki's comment.
As for heat treatment in the oven, well proteins become de-natured and set just above this temperature, somewhere nearer to 70*C, methinks. But it is a gradual process as the heat increases, so temperatures in the 60s will surely speed up all enzymatic reactions: these include both protease and amylase.
Does this help any? I'm aware of your great post, recently, which received undeservedly little response. I promised to come back to you on it and I will. Here's the link for anyone else prepared to take a second look: http://www.thefreshloaf.com/node/18488/amylase-activity-during-baking-serious-doubts
I'm really busy on all fronts at the moment, but I did have the discussion I mentioned, and will report back soon as I find the time
All good wishes
Andy
for your interest in the other thread and for your countinous help.
As for the other matter (still regarding enzyme activity) you were completely right: another biologist confirmed me that protease slows down as temperature decreases.
Best wishes for your work.
Nico
and I need time to mill it over in my head...
Still paying attention,
Mini
This is so fasinating. I look forward to more information flowing on this topic. What a great forum.
Learning a lot and loving it.......................Lyn
Hi folks,
Maybe of interest is the reply to Nico's question which I've just posted. You can catch the thread here: http://www.thefreshloaf.com/node/18488/amylase-activity-during-baking-serious-doubts#comment-124541
BW
Andy
Reinhart’s Whole Grain Bread promulgates a certain technique for most of the recipes. The technique involves a salted room-temperature (not cold) soaker, a refrigerated preferment he calls a biga, a relatively large amount of yeast in the final mix, and a relatively short fermentation.
Bran is loaded with protease, which weakens gluten. Since salt inhibits protease more than amylase, sugars are released in the soaker while the gluten is somewhat protected. Bran is softened. In some recipes, a mash is substituted for the soaker. In the hot (not scalding) mash, temperature is carefully controlled so that protease and other enzymes are de-natured, except alpha-amylase, and damage to gluten is not great. Protease denatures at a lower temp than alpha-amylase. The swollen and damaged starch granules are converted to sugar by the amylase.
Refrigeration slows enzyme activity, and so the gluten in the biga is somewhat protected. However, the yeast in the biga are not totally inactive, and they produce flavor-enhancing fermentation by-products, including acids. Bran is softened. The biga can be replaced by sourdough, and its moderate acidity will strengthen gluten.
Hi Nico and Ananda, thanks a lot. I think it all makes more sense to me. Nico, when you say "protease slows down with temparature" do you mean protease action and amylase action both increase with temp, but protease activity stops at a lower temp than amylase?
Thanks for the help!
or if at low temepratures it relents quicker or slower than amylase.
Sorry, I wish I knew more on the subject, but Charbono's post is a goldmine of usefule informations (thanks, Charbono!)