Hello, I am a homebrewer from Michigan, and I am looking for a cheap alternative to buying malt extract at $4/lb. I began looking into converting cornstarch, which is made up of long chains of glucose molecules, and found a method explained here, and also below: http://wiki.answers.com/Q/How_is_enzymatic_conversion_of_starch_to_glucose_syrup_done?#slide=54
I would like some help turning this process into more of a recipe that can be used by others, and I have several questions. I will also include the info below, along with a breakdown of the steps as I understand them, and my questions. I appreciate any help that you can offer. Thanks in advance.
To convert this polymer into its monomer, the amylase enzyme is used. The amylase enzyme can be classified into three categories: α-amylase, β-amylase, and glucoamylase. α-amylase will break the α-1,4-glycosidic bond randomly, giving molecules of dextrins. α-amylase can also break the α-1,6-glycosidic bond, but at a much slower rate (usually the enzym pullulanase is added to accelerate the breakage of α-1,6-glycosidic bond). β-amylase breaks the α-1,4-glycosidic bond from the non-reducing end, giving molecules of maltoses. And glucoamylase breaks the α-1,4-glycosidic bond also from the non-reducing end, giving molecules of glucose (Wiseman, 1985).
The α-amylase used is obtained from the bacteria B. subtilis or B. licheniformis, whereas the β-amylase is obtained from Aspergillus sp. and Rhizopus sp.
This conversion took place in a couple of steps:
First, we make a solution from the starch. In Wiseman (1985), a 30-40% solution w/w is preferred, which will -after the conversion reaction- give a 94-97% glucose in equilibrium mixture.
Then, we gelatinized this solution. Gelatinization is the process of breaking down the intermolecular bonds if starch molecules in the presence of water and heat.
After the starch solution is gelatinized (by heating), the solution became very viscous, just like the starch (kanji) we used to stiffen our clothing items. This is where the α-amylase is added, at 90 degreesdegrees Celsius and stirred for approximately 2 hours. This is the process of liquefying the starch. See, this α-amylase will break down the α-1,4-glycosidic bond, but not the α-1,6-glycosidic bond. Therefore, the reaction yields molecules of branched but short glucose. Branched molecules are soluble in water, whereas linear ones are insoluble. In other words, the branched molecule will make a less viscous solution that the linear ones. Hence the viscosity of the starch solution will decrease as the α-amylase works (Wiseman, 1985).
Liquefying can also be done with acid (HCl), in room temperature and acidic condition (pH 4.5-5). The downside of using acid is that acid can hydrolyze protein into amino acid, which will cause the browning reaction (or the Maillard reaction: reaction between amino acid and reducing sugar which will result in the presence of flavour. www.wikipedia.org/wiki/Maillard_reaction
). This is of course not desirable, because in order to get a pure glucose (or high concentrated, at least), the starch has to be really rid of impurities, where as an enzymatic reaction is specific and only the starch will be converted.
After the liquefying process, saccharifying is done with glucoamylase. The temperature for this step is 55-60 degreesdegrees Celsius. Saccharifying literally meant to convert into sugar (saccharose). Or, in more scientific words, saccharifying is the process of converting a sugar derivative or complex carbohydrate into a simple soluble fermentable sugar by hydrolysis.
The conversion is assumed to be done. A sample of the sugar is to be taken repeatedly at a time interval, and analyzed. Here we use the Fehling's reagent. The Fehling's reagen consisted of Fehling A (blue, copper sulfate solution) and Fehling B (colorless, potassium hydroxide and potassium sodium tartrate solution). This reagent specifically oxidize reducing sugars (glucose is a reducing sugar), and will result in a change of color from blue to red (cuprous sulfate). A standard solution of pure glucose is used to standarized the Fehling's reagent.
After obtaining the glucose concentration at every interval of the reaction, these data is plotted according to the Michaelis-Menten kinetics.
Step 1- Make a 30%-40% solution of corn starch to water ( How does this convert?)
Step 2- Heat mixture to 90C/194F, add Alpha Amylase and keep at that temp, and stir for 2 hours. (Will this work? http://www.midwestsupplies.com/amylase-enzyme.html
If so, how much do I add? If not, where can I find what I need? Do I have to stir continuously for 2 hours? Is there an acceptable temperature range if I am unable to keep it at exactly 194F?)
Step 3- Drop temp to 55-60C/131-140F and add glucoamylase. (How long do I stay at this temp? Where do I get glucoamylase? How much do I use?)
That's what I have so far. What am I missing? I apologize for the length and complexity. Thanks again.