Fast cook-continuous process for production of ammonia caramel color

Ammonia caramel coloring is formed continuously by pumping a heated stream of corn syrup through a reaction zone under pressure. 4MeI content and THI content are maintained at a low level by preheating the ammonia catalyst prior to injection into the reaction zone. Preferably ammonia catalyst is added to the reaction zone at a plurality of injection ports. This permits rapid formation of ammonia caramel coloring without increasing the 4MeI of THI content, and without hazing of the caramel color.

BACKGROUND OF THE INVENTION 
Caramel color is a product of the heat treatment of carbohydrates, 
typically sugars, usually in the presence of a catalyst. There are several 
types of caramel colors, for example, non-acid resistant and acid 
resistant types. The different types of caramel colors are chosen for 
their suitability for a particular end use. With soft drinks, 
acid-resistant type caramel colors are required. Malt beverages such as 
beer require non-acid resistant caramel. Non-acid-resistant caramel color 
particularly suitable for malt beverages and which is salt stable is 
produced using an aqueous ammonia or anhydrous ammonia catalyst. This is 
referred to as ammonia caramel color. 
Ammonia caramel color is generally produced using a batch type process. In 
a batch type process a large kettle containing up to 2000 gallons or more 
of a carbohydrate such as corn syrup is heated to boiling for about 8 to 
12 hours. Gradually the ammonia catalyst is added and the color forms. 
This is then slowly cooled and filtered and brought to the desired 
concentration. 
The batch process has several inherent problems. Since there is such a 
large mass of material, it is difficult to control the process conditions. 
The batch can burn and form an irreversible gelatinous mass which must be 
discarded and constitutes waste of the entire batch. Batch reactors also 
require a large capital investment to provide a reaction vessel suitable 
to hold such a large volume. Further the period of time required for a 
batch process is excessive. 
This time period could be reduced by increasing the reaction temperature 
which will increase the reaction rate. In order to do this, however, 
increased pressure is required. Such increased pressure causes hazing of 
the caramel thereby providing an unacceptable caramel color. 
A problem with caramel color is the production of 4-methyl imidazole 
(hereafter 4MeI) and 2-acetyl-4(5)-tetrahydroxy butyl imidazole 
(hereinafter THI). Over the past several years the Food and Drug 
Administration has limited the content of 4MeI in caramel color and THI 
content may soon be limited. It is believed that 4MeI and THI are reaction 
products of the carbohydrates in combination with the ammonia catalyst. To 
conduct the production of 4MeI and THI the ammonia catalyst must be added 
to the batch reactor very slowly. This is particularly difficult to 
control accurately; and even with this slow addition of the ammonia 
catalyst, unacceptably high levels of 4MeI and THI are sometimes 
encountered. Such high levels can require discarding of an entire batch of 
caramel color. 
Although apparently never commercially developed, methods have been 
disclosed to produce caramel color in a continuous manner under high 
pressure. For example, Meisel U.S. Pat. No. 3,214,294 and Ackermann U.S. 
Pat. No. 3,385,733 disclose continuous methods of producing caramel 
colorings. The Ackermann reference teaches forming a mixture of catalyst 
and polysaccharide syrup preferably corn syrup, preheating this to a 
temperature of 350.degree. F. to 1,000.degree. F., maintaining this 
reaction mixture in a continuous reactor under pressure for a period of 5 
to 300 minutes. Various catalysts including phosphoric and sulfuric acids 
and ammonium, potassium or sodium hydroxide are disclosed. Meisel also 
discloses using ammonium bisulfite as a catalyst. These methods are only 
for acid resistant caramel colors. 
Ammonia caramel produced according to the teachings of Meisel or Ackermann 
would have excessively high 4MeI and THI contents and further hazing would 
occur causing an unacceptably cloudy product. 
SUMMARY OF THE INVENTION 
The present invention is premised on the realization that ammonia caramel 
color can be produced continuously (as opposed to batch processing) by 
pumping a stream of carbohydrate syrup into a continuous reactor, heating 
the syrup to a temperature high enough to cause caramelization, 
maintaining the caramel at a high pressure and adding a caramelization 
catalyst such as either ammonia or ammonium hydroxide to the continuous 
reactor at a plurality of injection locations. At each injection location 
only a portion of the desired catalyst is added to the flowing stream of 
syrup. The amount added at any one location is controlled to prevent the 
pH of the syrup reaching any higher than about 6 or 7. The total amount of 
catalyst added at all of the injection locations combined is controlled to 
be the desired amount of catalyst to effect appropriate caramelization. A 
mixer is located at each injection location within the continuous reactor 
for agitating the syrup with the catalyst to insure an even reaction. 
By heating the temperature of the syrup to about 310.degree. to 320.degree. 
F. under pressure the reaction time can be reduced to about 10 minutes. By 
adding the catalyst at a plurality of locations under controlled 
conditions the 4MeI and THI content is maintained at acceptably low levels 
and hazing is surprisingly prevented. 
Further, the present invention is premised on the realization that in a 
continuous high temperature and high pressure method of forming ammonia 
caramel color, 4MeI and THI content can be reduced by preheating the 
ammonia catalyst prior to injecting it into a carbohydrate syrup. This 
further prevents hazing and provides a caramel color in a relatively short 
period of time. 
Surprisingly, all the advantages of a continuous process can be realized 
even though one would expect a high pressure ammonia caramel process to 
produce a hazy caramel color with unacceptably high 4MeI and THI contents. 
The advantages of the present invention will be appreciated in light of the 
detailed description and drawing in which:

DETAILED DESCRIPTION 
According to the present invention ammonia caramel coloring is produced by 
reacting a carbohydrate syrup with an ammonia catalyst in a continuous 
heated pressurized reactor. In the present invention any carbohydrate 
source normally used to produce caramel can be used. These carbohydrates 
(normally disaccharides or polysaccharides) include corn syrup, sucrose, 
dextrose, invert sugar, molasses or malt syrup. Normally corn syrup is 
used. Preferably the syrup is a food grade syrup. 
The method of the present invention permits utilization of syrup having a 
dextrose equivalent (DE) of below 80, and even as low as 70, 60 or 50 DE. 
These syrups are heated to above their boiling point (at ambient pressure) 
and reacted in the presence of a heated ammonia catalyst at elevated 
pressure as they are pumped through a continuous tubular reactor. 
Confinement within the reactor under elevated pressure maintains the water 
in the syrup in the liquid phase. Specific ammonia catalysts include 
anhydrous ammonia gas and aqueous ammonia, i.e. ammonium hydroxide. The 
catalyst and saccharide syrup are reacted in a continuous heated 
pressurized reactor which is shown diagrammatically in the FIGURE. The 
reactor maintains the water in the syrup in the liquid phase (i.e., the 
saturation pressure) and provides sufficient residence time for caramel 
color formation. 
The reactor 11 includes a preheater 12 which heats the syrup to form a 
pumpable fluid, an in-line tubular heater 13 designed to heat the syrup up 
to the appropriate reaction temperature, a series of tubular reactors 14 
and a cooler 15 all connected in series. 
The preheater 12 is an open stainless steel container 16 wrapped with steam 
heating coils 17. A mixer 18 is provided simply to promote heat flow 
within the stainless steel container 16. Bottom 19 of container 16 
communicates via a tube 21 with a pump 22 which directs fluid to the 
in-line tubular heater 13. The in-line tubular heater 13 is preferably a 
stainless steel tube 23 wrapped with a resistance heating element 24 (or 
alternately a steam jacket) and insulation 25. Heater 13 is mounted 
in-line between the pump 22 and the tubular reactors 14. 
The tubular reactors 14 form a continuous tubular reaction zone adapted to 
maintain the carbohydrate syrup under elevated pressure and permit 
catalyst injection at a plurality of locations. In this reaction zone the 
color formation occurs. In order to use less space the reaction zone is 
formed from six tubular reactors 26, 27, 28, 29, 30 and 31 connected in 
series by tubular "U" joints 32, 33, 34, 35 and 36. A first tubular "U" 
joint 39 connects an inlet end 37 of the first tubular reactor 26 to the 
outlet end 38 of the heater 13. Tubular "U" joint 39 includes a catalyst 
injector 41. The catalyst injector 41 includes a source of catalyst 42 and 
a metering pump 43 which forces catalyst through an in-line heater 44 into 
"U" joint 39 via catalyst injection port 45. 
The inlet end 37 of reactor tube 26 includes a static inline mixer 46 such 
as a Kenics brand mixer. This mixer is simply a spiraled piece of metal 
which has alternating left and right hand twists. The mixer 46 rests in 
the inlet end 37 of the reactor 26. 
First tubular reactor 26 is connected to the remaining six reactor tubes 
37-31 via the "U" joints 32-36. The 2nd and 3rd "U" joints 32 and 33 also 
include catalyst injectors 47 and 48 which are substantially the same as 
catalyst injector 41. Further tubular reactors 27 and 28 also include 
static mixers (not shown) at their inlet ends. 
U joints 34-36 may include catalyst injectors but this is unnecessary and 
generally not preferred unless the catalyst is injected at a lower or 
ambient temperature. In this situation the catalyst must be added in 
smaller amounts requiring more injectors. 
The final or 6th reactor 31 connects to the cooler 15. The cooler 15, which 
is a water jacketed tube, is connected inline between the 6th tubular 
reactor 31 and a discharge valve 51. The valve 51 discharges into a gas 
liquid separator 52. The valve 51 is used to control the internal pressure 
of the reactor. 
In one embodiment the reactor tubes are each 10 feet in length having a one 
inch internal diameter. The static mixers are each one foot in length. It 
is possible of course to increase or decrease the length, number and 
diameter of the tubular reactors as long as under reactor conditions (flow 
rate, temperature, pressure and reaction time), the proper amount of color 
development takes place. 
According to the process of the present invention, food grade carbohydrate 
syrup such as corn syrup is added to the preheater 12 where it is heated 
to a temperature of at least about 200.degree. F. although it can range up 
to 330.degree. F. Pump 22 draws the heated syrup from the preheater 12 and 
pumps it into the in-line heater 13 which in turn heats the syrup to 
250.degree. F. to 350.degree. F. (at least above the ambient boiling point 
of the syrup) and preferably 310.degree. F. to 320.degree. F. The pump 22 
creates a flowing stream of carbohydrate syrup which passes from the 
heater 13 through the U joint 39 into the first tubular reactor 26. At the 
U joint 39 a first portion of the ammonia catalyst is injected into the 
flowing stream of carbohydrate syrup. 
The catalyst is drawn from the supply tank 42 and passed through in-line 
heater 44 and into the tubular reactor 26 through the injection port 45. 
The catalyst is heated to at least the temperature of the syrup. 
Preferably the catalyst is heated to from about 300.degree. F. to about 
330.degree. F. prior to injection. The syrup then passes through the first 
tubular reactor 26 which in this case is approximately 10 feet in length 
and through second U joint 32 to the second tubular reactor 27. Again 
catalyst is injected into the second reactor tube 27 by a second catalyst 
injector 47. The temperature of the catalyst is again established at about 
300.degree. F. to 330.degree. F. The syrup passes through the third U 
joint 33 where heated catalyst is again added and then into the third 
tubular reactor 28. The syrup passes seriatim through the fourth, fifth 
and sixth tubular reactors 29-37. 
Catalyst injectors 41, 47 and 48 control the rate of addition of catalyst. 
The total amount of ammonia catalyst which needs to be added will of 
course vary depending upon desired color formation. Generally, if aqueous 
ammonia is added (28% NH.sub.4 OH by weight and 0.9 specific gravity) to a 
corn syrup solution (80% solids 1.4 specific gravity) the volume to volume 
ratio of aqueous ammonia to syrup will be about 30/70. One third of the 
desired amount of catalyst is added at each injection port. The reactor 
tubes combined act to create a long reaction zone to provide the required 
reaction time for color development. It is preferred that all of the 
ammonia catalyst be injected within the first 80% of the reaction zone. 
More preferably, the catalyst should all be injected within 50 to 70% of 
the reaction zone. In the present invention, the length of the reaction 
zone is basically interchangeable with reaction time. This is because the 
flow rate through the reaction zone is constant. Accordingly, all of the 
catalyst should be injected within the first 80 % of the reaction time and 
preferably within the first 50% to 70% of the reaction time. 
The reaction time, i.e. the time the syrup is maintained at the elevated 
temperature and pressure will vary from about 1 to about 100 minutes or 
more depending on the reaction temperature and desired color formation. 
More typically the reaction time will be 5-15 minutes. If the catalyst is 
not heated, it is critical that not all of the ammonia be injected at any 
one injection port. Preferably the total amount of ammonia injected at any 
one injection point will not be more than that which would raise the pH of 
the carbohydrate syrup to 6 or at most 7 (preferably about 5). If the 
catalyst is heated to at least about 300.degree. F. more catalyst can be 
added at fewer injection ports. 
After passing through the sixth tubular reactor 31, the stream of 
saccharide syrup passes through the in-line cooler 15. The in-line cooler 
15 is simply a water jacketed stainless steel tube which preferably 
reduces the temperature of the stream of syrup while maintaining the 
pressure. Preferably the cooler will reduce the temperature to about 
180.degree. F. After passing from the cooler the syrup which now is 
developed into a caramel color passes through valve 51 to a gas liquid 
separator. Control of the valve acts to maintain the internal pressure at 
a desired state. 
Generally the internal pressure of the reaction zone will be maintained by 
the pressure release valve at about 60 to 100 psig. This will of course 
vary depending on flow rate and reaction temperature. 
The present invention will be further appreciated in light of the following 
examples which disclose formation of caramel color using the previously 
described reactor. 
EXAMPLE 1 
Food grade corn syrup (62DE, 82.degree. Brix) was added to the preheater 
and heated to about 250.degree. F. It was pumped into the heater at a flow 
rate of 500 cc per minute and heated to 300.degree. F. Aqua ammonia (29% 
NH.sub.4 OH) was injected through the three ammonia injection ports at a 
rate of 50 cc per minute. The aqueous ammonia had been preheated to a 
temperature of 330.degree. F. The reaction temperature within the reaction 
zone reached about 339.degree. F. The reaction pressure was maintained at 
100 psig and the reaction time was 12 minutes. The caramel emitted from 
the gas release valve had a color of 0.086 abs 610 nm at 0.1% w/v; a 
specific gravity of 1.31, pH of 5.21 and a 4MeI content of 45 ppm. This 
color was beer and salt stable. In other words, when added to either beer 
or a concentrated salt solution, it remained dissolved and did not 
precipitate or cause the beer or salt solution to become murky. 
EXAMPLE 2 
Food grade corn syrup (62DE, 82 Brix) was added to the preheater and heated 
to 270.degree. F. and pumped at a rate of 500 cc per minute into the 
reactor heater. It was heated to 330.degree. F. at a pressure of 95 psig. 
Aqueous ammonia (29% NH.sub.4 OH) was preheated to 327.degree. F. and 
injected through the three ammonia injection ports at a flow rate of 80 cc 
per minute through each injector. The reaction time was 14 minutes and the 
produced caramel had a color of 0.105 abs. 610 nm at 0.1% w/v. The 
specific gravity was 1.31 and pH 4.41 with 4MeI content of 54 ppm. Again 
this is beer and salt stable. 
EXAMPLE 3 
An alternate method of practicing the present invention is to first run the 
syrup through the reactor adding all the requisite catalyst in a first 
pass. Thereafter, to develop further color, the syrup is again passed 
through the reactor without adding further catalyst. The syrup is heated 
under pressure, mixed with catalyst and cooled in the first pass. It is 
then heated and cooled again in the second pass where the color forming 
reaction is completed. In this example, food grade corn syrup (62DE, 
82.degree. Brix) was added to the preheater and pumped at a rate of 500 cc 
per minute into the reactor heater where it was heated to 330.degree. F. 
and then passed into the reactor zone. Aqua ammonia (29% NH.sub.4 OH) was 
heated to 326.degree. F. and injected into the reaction zone at a rate of 
125 cc per minute. On the first pass it was reacted 13 minutes to produce 
a caramel color after the first pass of 0.11 abs 610 nm at 0.1% w/v with a 
specific gravity of 1.27 and a pH of 6.3 with 218 ppm of 4MeI. This 
solution was cooled to ambient temperature and passed again through the 
reactor. In this second pass the flow rate was 1,000 cc per minute and the 
reaction temperature was 302.degree. F. The reactor pressure was 
maintained at 65 psig and the reaction time was 6.5 minutes. Caramel 
properties were color 0.13 abs 610 nm at 0.1% w/v specific gravity 1.264, 
pH 5.0 4MeI content 210 ppm. This again was beer and salt stable. 
According to this last example the color content of the caramel color is 
increased by cooling the catalyst syrup mixture prior to total formation 
of color and subsequently reheating the catalyst syrup mixture. This 
permits the formation of a deeper color without excessively increasing the 
4MeI content relative to the color intensity. 
In all of these examples the THI content, which is generally related to the 
4MeI content, should be less than 60 ppm with color intensity of less than 
about 0.1 abs at 610 nm, and generally below 20 ppm at about 10-15 ppm. 
Using prior art methods frequently produces caramel with THI contents in 
excess of 100 ppm in such a color concentration. Moreover, hazing did not 
occur in any of the examples. 
The caramelization reaction once started is exothermic and temperature 
control is required. Preferably the temperature of the reacting syrup 
catalyst mixture is controlled by controlling the pressure via valve 51. 
The temperature could also be controlled by cooling the reaction tubes. 
This is less preferred because a temperature differential is created 
within the reaction tube. This tends to increase 4MeI and THI content. 
The above methods provide a low cost, rapid method of producing ammonia 
caramel while reducing the 4MeI or THI content. Thus the present invention 
provides a quick simple method of producing ammonia caramel. 
The present invention can also be practiced using high solids content syrup 
with anhydrous ammonia. This modification disclosed in a co-pending 
application permits formation of a darker color which is clear and salt 
and beer stable. Accordingly, preferably the solid content of the 
carbohydrate syrup should be at least about 75% and more preferably the 
solids content should be 80% or higher. By controlling the water content 
an improved caramel color is produced. 
Accordingly, having described my invention,