Production of Jerusalem Artichoke Flour

This invention relates to production of flour from tubers of the Jerusalem artichoke. Flour derived from Jerusalem artichoke tubers is a nutritionally valuable food since the flour can contain as few as seventy percent or less calories than are found in an equivalent of weight of wheat flour, is high in fiber content and contains significant amounts of minerals, niacin, riboflavin, and ascorbic acid. Prior attempts at producing such flour have encountered difficulties in the grinding step and have produced an unduly darkened flour which has had high levels of the characteristic Jerusalem artichoke flavor.

For example, Mr. Tom Lukens at page 9 of "The Artichoke Connection", Vol. 2, No. 1, Winter, 1984 states: "They found (as did everybody I talked to on flour), and this is something to think about, that if you're going to make flour, you better make sure that you have the stuff bone dry before you run it through the mill because it caramelizes and the hardest rocks of sugary sticky stuff that you can't beat up into a powder unless it is really dry. Of course the cost of drying that last 10%-15% moisture are pretty great. So you can't skimp on drying. If you don't have the percentage moisture down there, you're not going to be able to grind the stuff for flour very well." Surprisingly, the present method permits ready grinding of particles of Jerusalem artichoke tuber which contain much higher amounts of water and permits production of a flour which, after grinding, can still contain 13% moisture without producing any caramelized lumps in the process. Moreover the process requires no browning inhibitor such as sulfur dioxide or ascorbic acid to produce a light colored flour. The sensory quality of the flour is excellent; it has an appearance comparable to whole wheat flour, is free-flowing, has little or none of the characteristic Jerusalem artichoke aroma and essentially no detectable Jerusalem artichoke taste after baking.

It is, therefore, an object of this invention to provide a process whereby a flour can be produced from Jerusalem artichoke tubers without the necessity for excessive drying and which avoids problems, heretofore encountered in grinding.

It is further object of this invention to produce a low calorie product which has a high content of dietary fiber.

The present invention is for a process for production of flour from Jerusalem artichoke tubers which comprises: reducing the tubers to particles having an average surface to volume ratio of not less than about 25 cm.sup.2 to 1 cm.sup.3 and exposing said particles to a solution comprised of water acidified to a pH not greater than about 4; subjecting the particles to a series of pressings at increasing pressures ending in a final pressing at a pressure of not less than about 6 atmospheres, gauge, wherein, between each pressing the pressure is relaxed and the particles are loosened; washing the particles with water at least once after exposure to the acidified water and before the final pressing; drying the particles at a temperature not greater than about 200.degree. F. to a moisture content not greater than about 13% by weight of the flour; and grinding the dried particles to a flour.

The tubers may be reduced in size to the required surface to volume ratio by shredding, grinding, grating, chopping or any other method which yields a particle, shred or other shape with an average surface to volume ratio not less than about 25 cm.sup.2 to 1 cm.sup.3. It will be understood that these surface to volume ratios are necessarily the average surface to volume ratios since any of the methods used to reduce the size of the tubers will yield a range of particles sizes a few of which may have a significantly smaller surface to volume ratio than 25 cm.sup.2 to 1cm.sup.3 with many much smaller particles controlling the average surface to volume ratio. It should be noted that the particle surfaces may be highly irregular, as when grinding has been utilized to produce the particles, thus leading to a high surface area. It may also be noted that the freshly ground particles appear to be much larger than they are since the juice-laden particles tend to aglomerate and clump together. However, on modest drying the particles readily separate and it is seen that the average particle size is much smaller than the agglomerated clumps would lead one to believe on casual examination. The surface to volume ratio is an important factor for two reasons. The small particles facilitate maximum contact with the acidified water, as hereinafter described, and permit maximum extraction of the juice of the tubers when compressed. Methods which avoid or minimize contact of the tubers and/or particles obtained therefrom with corridible surfaces, particularly corrodible metallic surfaces are preferred. The process is preferably carried out in corrosion resistant equipment such as stainless steel or plastic or glass lined equipment.

To inhibit color formation the particles are exposed to a solution comprised of water acidified to a pH not greater than about 4, and preferably to a pH of about 3. Although solutions comprised of water acidified to a pH below 3 are not excluded from the practice of the invention, lower PH's are not required to obtain the described product. Traditional browning inhibitors such as sulfur dioxide, ascorbic or erythorbic acid are not required. In order to provide immediate contact with the freshly cut or torn surfaces of the particles it is preferred that the acidified water be added along with the tubers to the grinder, shredder, or other device by which means the tubers are reduced in size in the presence of the acidified water and are discharged from the grinder, shredder or other device along with the acidified water. Although this is a preferred method, satisfactory results can be obtained by rinsing the particles with the acidified water immediately after they have been reduced to the requisite size. It should be noted that the pH of the juice is about 5 and it is necessary that the acidified water have a lesser pH to avoid darkening of the particles.

The solution comprised of acidified water may be acidified with any inorganic or organic acid, salts thereof or combinations of acids and salts capable of acidifying water to a pH of about 3 or less. Sulfuric acid, hydrochloric acid and phosphoric acid are satisfactory inorganic acids. Acetic and citric acids exemplify organic acids which may be used as acidfying agents, and, as is well known, there is a variety of combinations of salts with and without acids (buffers) which may be used to acidify water to the desired pH.

The particles are pressed at progressively higher pressures to expell juice from the particles. This is done in a series of steps with the pressure being released and the particles being loosened or separated from the compressed mass between each pressing. This loosening or separation minimizes pockets of uneven pressure and juice and tends to maximize removal of juice from the particles. The final pressing is at a pressure of at least 6 atmospheres, gauge. The particles after being exposed to the acidified water are washed with water at least once prior to the final pressing. It is preferred that the particles be washed between one or more of the pressing steps after the pressure has been released and the particles have been loosened or separated; in such case the particles may be washed in the press.

In a preferred embodiment of my invention the particles along with the acidified rinse water are placed into the press and subjected to a first pressing at a pressure of between 11/2 atmospheres, gauge, to 21/2 atmospheres, gauge, the pressure is then released and the particles loosened, the particles are then pressed a second time at a pressure between 21/2 to 41/2 atmospheres, gauge, followed by releasing the pressure and loosening the particles. The particles are then pressed a third time at a pressure of not less than about 6 atmospheres, gauge. The particles may be washed after either or both of the first or second pressings. It is to be understood that for purposes of this invention the steps of "loosening" or "separating" are intended to include loosening or separating done concurrently with or by means of the water wash. The water wash is an important aspect of the invention since I have found that this step produces a lighter colored product, reduces the characteristic flavor and odor of Jerusalem artichoke in the final product, promotes ease of grinding, reduces the carbohydrates in the flour by at least 25%, and, since the principal carbohydrate in Jerusalem artichokes is inulin, which may be regarded as having no available dietary calories, the actual reduction in available calories may be much greater than 25%.

After the final press, the particles are dried by conventional means such as a forced air, or rotary, or fluid bed or belt drier, cyclone, conventional or microwave oven. The particles, as they come from the press tend to aglomerate, and, for reasons not fully understood, the lumps or agglomerates have a tendency to darken during drying. Therefore, for optimum quality of the flour it is preferred that any lumps, large particles and agglomerates be removed prior to drying.

It has been observed that the undried particles tend to darken upon standing and a lighter colored final product is obtained when the particles are moved from the final press to the drier without undue delay. It is preferred that the particles be removed from the final press directly to the drier.

The particles are dried at an elevated temperature. To avoid excessive darkening of the particles the temperature should not exceed about 200.degree. F. The particles are dried to a moisture content of not greater than about 13% by weight based on the weight of the flour, preferably to a moisture content of not greater than about 10% by weight based on the weight of the flour.

Using the above-described process I have produced a flour, light in color and having little or none of the characteristic Jerusalem artichoke aroma which, typically, has the composition: per 100 grams of flour given in the following table:

It is to be understood that the foregoing description of the specific embodiments of the invention are illustrative only and are not intended to limit the scope of the invention and the ambit of the claims inasmuch as additional embodiments will be readily apparent to those skilled in the art.