Potato Starch

The Brewer’s Journal  February, 1917

Potato Starch as a Partial Substitute for Malt.

                                                                                     By V. Koudelka.

Among the malt adjuncts to which the Austrian brewing industry has been obliged to resort, cane sugar was the first to come under consideration.  It gave very satisfactory results, and from the standpoint of stability, purity, and even taste, the present “war-sugar-beers” are almost equal to the former all-malt beers.  Sugar, however, is also scarce, and the Government permits only an addition of 30 per cent.  This condition and the very scanty quantity of malt allotted, compelled the brewers to seek another adjunct, and attention is now being given to potato starch, or potato starch flour.

Potato starch is obtained from cleaned and grated potatoes by a washing process whereby the starch is separated from the fibre particles and other components of the potatoes.  The washed starch is cleaned and assorted by various processes into prime starch, “seconds” and “thirds”, or “sludge starch.”   To make the dry starch, the washed, raw starch is mixed with water to a milky consistency, and is then centrifugalised and dried until it contains only about 20 per cent moisture, being then ground and sifted.

Potato starch nearly always contains some acid, which finds its way into the finished product in the natural way or may be the result of artificially added inorganic acids.  The organic acids cannot be entirely washed out, and even during the process of manufacture organic acids are liable to be formed by bacterial fermentation.  When damaged or rotten potatoes are used, the starch factories frequently add either sulphurous (H2SO3) or sulphuric (H2SO4) acid, which if improperly washed out, is traceable in the finished product.  Good potato starch or prime meal should be technically free of acid that is, not more than 5ccm. of n/10 KOH (potassium hydroxide) should be required for the neutralization of 100 g. of starch.  Inorganic acids should not be present at all.

According to König, the chemical composition of commercial starch is as follows: — Water 17.33%; proteins 0.43%; nitrogen-free extractive substances 81.77%; ash 0.35%; raw fibre 0.04%. 

At 46.2o C potato starch begins to swell noticeably, at 58.7o C, it starts to become pasty, and is completely gelatinized almost immediately at a temperature of 62.5o C.  According to Lintner, 100 parts of potato starch figured on dry basis, produce under the action of diastase at 50o C 0.13%, at 55o C 5.03%, at 60o C 52.68%, and at 63o C 90.34% of starch conversion products.

These data show in the first place that it is absolutely necessary that the potato starch be mixed with cold water, for with warm water it tends to forms lumps, which are very difficult to break up by mechanical stirring, and resist complete gelatinization even at the later stages of mashing, their extract being therefore entirely lost.  In the second place, it is necessary to employ temperatures at which the starch is most completely converted, i.e., about 63o C, at which temperature the starch gelatinizes almost immediately.

The operation in the brewhouse will, therefore have to be so arranged that the mixture of cold water and starch is either treated as a separate mash – which method would seem preferable for large plants where considerable quantities of starch are used – or, in small breweries, by adding the cold mixture direct to the initial mash, so that it will permit it to be modified and converted with the later.

The potato starch may also be mixed with cold water in the mash-tun and the malt added later.  For this method, however, a propeller that works well is essential.  In breweries where the mash-tun also serves for draining the wort, this method is advisable, as the starch readily settles while the mash is kept on rest, and is apt to get below the false bottom, and from whence it can only, with difficulty, be brought out again by the stirring apparatus, and thereby escape conversion during the mashing process.

Should it be decided to boil the potato starch separately in the form of a raw grain mash, the method of working would be as follows:  The potato starch is thoroughly mixed with cold water in the mash-tun, the stirring apparatus being worked rapidly, and then a quantity of malt-grist equal to about 20-30% of the quantity of the starch is added.   A proportionate quantity of malt-mash that has in the meantime been prepared in the mash-tun could also be used instead of the malt-grist.  The raw grain mash is then heated to gelatinization temperature (65o C) at which, however, no rest is needed immediately because the paste forms almost immediately, it would rather be advisable, in view of the simultaneous use of sugar, to bring the temperature as quickly as possible to 70-71o C at which, while gradually raising to 75o C, the conversion and saccharification of the starch take place.  This requires more or less time according to the quantity of starch added.  According to whether this raw-grain mash is to be used in place of hot liquor or as an initial mash, it is brought to boiling and added to the mash, or is boiled for a further 20-25 minutes in order to get the full yield from the malt added.

When the starch is added direct to the initial mash, the method is working depends upon the local conditions.  The starch may either be mixed with cold water in the mash-tun, and after the temperature of the malt-mash has been raised to the correct degree by the addition of hot water, the first mash is drawn and added to the raw-grain mash in the mash-tun, or else the starch is mixed with cold water in a separate vessel and added to the first mash.  The first mash is then treated and saccharified as above.

These methods have proved successful in experiments both in the laboratory and in practical brewing.  It should be noted that when potato starch is used –  viz. on account of the smaller quantity of malt, there is a thinner layer of grains in the draining vat.

When using malt adjuncts the proteins of the wort are derived exclusively from the malt.  It will therefore be advisable, to conduct the mashing process at temperatures which favor the modification of albuminoids so that the greatest possible amount of these important constituents will be brought into the wort and subsequently into the beer.

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