What does an iodine test for starch show. Sweet wort preparation

Iodine test is one of the important points when cooking home beer. Why do an iodine test and what does it show? How to do it right? What are the subtleties when conducting an iodine sample of the wort. Let's deal with these questions and, of course, do not forget one more important point: What to do if the iodine test is positive. So, let's start in order.

Wort iodine test - what is it?

An iodine test is a process during which you take not a large number of wort (literally half a teaspoon) and drip a drop of iodine solution into it. This is best done on a white flat plate. Then mix the wort with iodine with a cotton swab or any other object and look at the result. As you can see, conducting an iodine test is very simple. All you need to do an iodine test is the mash you make and the iodine that every home has. If you don't have it, just go to your nearest pharmacy and buy it.

You can look at how I do an iodine test when brewing beer.

Why do an iodine test?

An iodine test is done for only one purpose - to determine the presence of starch in the wort. Here we need to understand the process of mashing. During mashing, fermentation takes place and each temperature pause is maintained in order for certain enzymes to do their job. During a temperature pause in the range of 72-75 degrees, starch is sucrose and dextrins are formed. An iodine test carried out after the end of this pause indicates the presence of starch in the mash. If the iodine test is positive, then there is still starch left in the mash, and the current temperature pause should be extended, if the test is negative, then the starch is completely sugared and you can continue mashing and proceed to the next steps.

Results of the iodine mash test.

What does it mean that the test is positive? This question put me in a stupor when I first read about the iodine test. It seemed to me that it was all very complicated and that something had to be studied and compared ... not at all. The iodine test is a very simple diagnostic method. When you mix iodine and mash, what happens chemical reaction. Iodine reacts with starch and changes its color from brown to purple. Simply put, if after mixing, iodine turns purple, then there is still starch in the mash and it is worth extending the pause, after which the test must be repeated. If the color has not changed, then the saccharification process is completely completed and you can move on.

How to do an iodine test?

I think from all of the above, you have already understood that everything is quite simple, but some manage to do simply unthinkable things. Let's summarize, and describe step by step how the iodine test is done during mashing.

1. After the end of the temperature pause in the range of 72-75 degrees, select 1 teaspoon of the wort.
2. Pour the selected wort onto a flat white plate.
3. Add 1-2 drops of iodine to the wort (if you add a lot of iodine, you simply will not notice the difference, even if the starch is still left)
4. Mix iodine and wort with a cotton swab
5. Wait 20-30 seconds and look at the sample
6. If the color of the sample has not changed, continue brewing the beer, if the solution has changed color and turned purple, extend the temperature pause for another 10 minutes, then repeat the iodine test.

Conclusion.

As you can see, the iodine test is an important step in brewing homemade beer, and now you know how to do the iodine test correctly. Happy cooking and tasty beer!

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Preparation of sweet wort.

To the big 10 -liter pot (mash tun) is poured 0,5 liters malted milk and the same cold water. The mixture is stirred with a stirrer (paddle), slowly adding the boiled starch mass, and making sure that the temperature does not exceed 58 0 WITH. At a higher temperature, the mass of the mash is cooled by washing the surface of the vat cold water or by passing water through a serpentine placed inside the mash tun. While continuing to vigorously mix the contents of the mash tun. At the end of the mixing of malted milk and starch mass, the temperature should not exceed 62 0 C. Then add the rest of the malted milk. 0,5 liters and mix the mash for 5 minutes. Consumption rates of malt and water for 1 kg. supplies are shown in the table 6 .

Table 6
Malt and water consumption rates for mashing 1 kg of raw starch

Mashing the main congestion. This operation is one of the main ones in the process of obtaining alcohol. Its purpose is to provide starch transformation, which includes three stages: gelatinization, liquefaction (dissolution) and saccharification. For this purpose, malted milk is used. The mash is heated to a temperature of 52-62°C and maintained at this temperature for 7-8 hours.

Saccharification of starch. This operation depends on a number of conditions, in particular on whether pure starch or raw materials are used. In the second case, the duration of saccharification will be much longer in time. Flour saccharification lasts 7-8 hours, saccharification of potato mash - only 1-2 hours.

It is important not to overheat the wort over 65°C. To determine the end of saccharification, a check is made - an iodine test. The concentration of sugars in the finished wort must be at least 16%, which corresponds to a solution density of 1.06. During mashing, malted milk is mixed with boiled starch mass, the starch is saccharified, the mash is filtered and the wort is tested. Then yeast is added and left to ferment.

Mixing malted milk and starch mass. This operation is not particularly difficult, but requires a clear implementation of the recommendations. Pour 0.5 liters of malted milk and the same amount of cold water into a 10-liter saucepan (mash tun). Then the mixture is vigorously stirred, after which the boiled starch mass is slowly added. Constantly stirring, make sure that the temperature does not exceed 58 ° C. If the temperature has risen above this norm, it is necessary to cool the mash by washing the surface of the tun with cold water (if there is no coil placed inside the mash tun).

permanent intensive mixing- an indispensable requirement of this operation.

The rest of the malted milk is then added and the mash is mixed for 5 minutes. The table below shows the consumption rates for malt and water.

Supply saccharification. A mixture of starch mass and malted milk is kept in a water bath for 4 hours at 65°C, constantly stirring.

Consumption rates of malt and water when mashing 1 kg of raw starch

The concentration of sugars in the wort is then measured and the presence of unsugared starch in the mash is determined by performing an iodine test. Maintaining a temperature of 55-65°C, saccharification is carried out until the iodine test shows the absence of unsaccharified starch in the mash.

The time of saccharification of starch mash can be different and depends primarily on the quality of the malt. When using old malt or technology violations, the saccharification process can take up to 20 hours. Usually, this operation takes 3-4 hours.

In privately built houses, the mash is usually placed in a cooled oven (up to 60 ° C) overnight.

The concentration of wort after saccharification should be in the range of 16-18% sugars (1.060-1.070 g/cm3).

Wort test. This operation includes an iodine test, measurement of sugar concentration and acidity.

Iodine test. As a rule, on the surface of the mash after saccharification there is a clarified layer of wort, which is used for sampling. A small sample (10 g) of must is taken. If the solution contains a large amount of impurities, then it must be filtered.

The taken sample is placed in a saucer, adding 2-3 drops of iodine tincture. After stirring, visually evaluate the quality of saccharification. If no color is detected and the iodine solution does not change the light brown color, then we can assume that complete saccharification has occurred.

If a red color is detected, then the saccharification process is not finished. It must be continued. If a purple coloration occurs, then the saccharification process is going badly. You need to add malted milk.

An iodine solution is prepared as follows: 0.5 g of iodine, 1.0 g of potassium iodide and 125 ml of water are taken. Everything is thoroughly mixed and stored in a dark place. In the absence of potassium iodide, only a solution of iodine can be dispensed with, but the red and purple color will appear in this case to a lesser extent.

Measurement of sugar concentration. The clarified layer of the wort is drained, filtered through a cloth and poured into a 200 ml graduated cylinder. At a wort temperature of 20°C, a measurement is carried out using a saccharometer (hydrometer) placed in the wort. The table below determines the concentration of the wort. A wort with a sugar concentration of at least 16% and a sweet taste is considered to be of high quality.

Measurement of the acidity of the wort. A small sample of clarified wort is taken and indicator paper is placed in it, changing its color depending on the degree of acidity. You can determine the acidity by taste.

Density and concentration of sucrose solutions

The wort of normal acidity has a slightly acidic taste.

Mature yeast addition. Having cooled the wort of the mash to 30°C, add mineral nutrition (ammonium chloride 0.3 g/l) and mature yeast (yeast mash), stir and continue to cool to a temperature of 15°C. At this temperature, the wort is poured into a fermentation tank and put to ferment in a dark place.

α-amylase breaks the chains of amylase and amylopectin mainly into dextrins with 7-12 glucose residues. From the end groups of the resulting chains, ß-amylase splits off double groups (maltose) (see Fig. 3.25, c). This process inevitably takes longer than the separation of longer chains by α-amylase.

Due to the different chain lengths, in addition to maltose, other sugars, glucose and maltotriose, are also formed.

In all cases, the cleavage of substances stops at 2-3 glucose residues before the 1,6-compounds of amylopectin, since these 1,6-compounds cannot be cleaved by either α- or ß-amylase. These limiting dextrins are always found in normal must.

Malt does contain an enzyme. (limiting dextrinase), which is capable of dissolving, in addition to 1,4-compounds, also 1,6-compounding, but at the optimum temperature for this enzyme of 50-60 ° C, it hardly matters for the process of obtaining saccharified mash. At 70°C, only a weak activity of limiting dextrinase is detected.

When starch is cleaved by malt amylases, the following occurs.

α-amylase breaks down long chains of starch into shorter dextrins. It works optimally at 72-75°C and is rapidly destroyed at 80°C. The optimum pH value is 5.6-5.8.

ß-amylase separates maltose from the unreduced ends of the chains, while glucose and maltotriose are also formed. It operates optimally at 60-65°C and is very sensitive to more high temperatures, already at 70°C it is rapidly inactivated. The optimum pH value is 5.4-5.5.

Starch digestion should be controlled as undigested starch residue and larger dextrins cause gelatinous haze in the beer.

The control of starch splitting is performed using a 0.02-n solution iodine(alcohol solution of iodine and potassium iodide). This check is called iodine test and is always done with a chilled mash sample. (In domestic brewing it is customary to use water solution iodine and potassium iodide. - Note. ed.) The iodine test is based on the fact that an iodine solution at room temperature gives a dark blue to red coloration with starch and high molecular weight dextrins, while all sugars and smaller dextrins do not change its yellow-brown color.

High-molecular and medium-molecular branched dextrins give with iodine also violet (to red) iodine staining. This coloration is not always easy to distinguish, but when present, the wort can still be characterized as giving a normal reaction with iodine. The more accurate Windisch iodine test monitors the presence of these dextrins by precipitating them with ethanol, then removing the ethanol, redissolving the dextrins in water, and staining them with iodine solution. This method is used most often in problem situations.

The brewer must be able to correctly evaluate the iodine sample. If the iodine solution, when mixed with the mash, no longer gives color, then such a mash is designated as saccharified, that is, it does not change the color of the iodine solution (normal reaction to iodine). The breakdown of starch molecules to a state in which no staining with iodine solution is observed is called saccharification.

By saccharification, we mean the complete breakdown of liquefied starch by amylases into maltose and dextrins. The determination is carried out using an iodine test (Fig. 3.26).

The starch breakdown products formed during mashing differ significantly in fermentability with brewer's yeast. For example,