12 MASS. EXPERIMENT STATION BULLETIN 287 



Tilt' tuble is lai'gely solf-expliiiiatory. Tliere was apparently no injury to the 

 ((uality of the frozen pack when held 12 hours at 45° F. or 6 hours at 80° F. 

 In fact a short holding period dissolves all the sugar, and by allowing osmotic 

 action to proceed, thoroughly impregnates the fruit with sugar. This action seems 

 to aid in overcoming enzymic discoloration from oxygen within the fruit. Sim- 

 ilarly, delayed freezing draws out some of the juices from the fruit so that the 

 appearance is similar to a syruj) pac^k but without the disadvantage of added 

 water. 



Up to 6 hours holding at summer temperatures did not injure the quality 

 , of the fruit. However, after 12 hours, there was a lack of fresh fruit flavor and 

 Cii too much bleeding of the fruit; and after 24 hours, slight yeasty fermentation 



V and surface molding had begun. Obviously it is better to hold strawberries in 



V a pre-cooler than at room or outside temperatures because of the deteriorative 

 ^^ influences of the latter. During the holding jjeriod the fruit appears flrst to give 



up juice to a certain point and then reabsorbs it so that finally equilibrium is 

 reached, in the c'ase of a 2:1 pack of strawberries this point is at a syrup con- 

 centration of about 35-36 per cent sugar. 



The Effect of Vacuum Packing 



With a view to overcoming surface discoloration in frozen strawberries, 27 

 one-gallon cans of strawberries were packed in 1930 at Gloucester, where a 

 vacuum sealing machine for gallon cans was available. The berries were well 

 I colored, mature, yet firm in texture. Katios of 2:1, 2^'^:\ and 3:1 of fruit to dry 

 ,1 sugar and 80, 65, 50 and 40 per cent syrup packs were employed. \'acuums of 

 10-12 and 18-22 inches of mercury were used. Controls in the usual friction-top 

 unsealed cans were likewise packed. The berries were frozen at 0° F. and stored 

 at that temperature for 11 months before defrosting and examination. 



Inasmuch as the results showed few essential differences ffom other sugar 

 or syrup packs already recorded in Tables 1, 2 and 3, the data are not given. 

 The outstanding observation was that the vacuum-packed fruit showed no sur- 

 face discoloration. That is, the air (oxygen) in the headspace of the cans had 

 been largely removed by vacuumization, and did not cause deleterious oxidations 

 which injure both color and flavor of the surface layer of fruit. 



The fruit packed at vacuums of 18-22 inches was somewhat better than that 

 '\ packed at lower vacuums, probably because of more effective oxygen removal. 

 o» As stated previously in this bulletin, the 2^-^:1 and 3:1 dry sugar packs were con- 

 sidered best from the ice cream manufacturer's viewpoint; and of the syrup 

 packs, the 40 and 50 per cent were considered superior in appearance and flavor 

 both after defrosting antl when manufactured into ice cream. The 80 and 65 

 [)er (!ent syrups gave imsatisfactory packs in that both were too sweet and re- 

 quired too large quantities to cover the fruit. The berries also floated .so easily 

 that they could not be readily packed into the cans. Vacuums in excess of 20 

 inches could not be secured in one-gallon (No. 10) cans because of paneling 

 effects. That is, the sides of the can would yield to the high vacuum and be- 

 come concave, thus reducing the can volume as well as vacuum. Several cans 

 were totally ruined when attempts were made to secure vacuumization at the 

 25-inch level. With smaller cans, it would be feasible to use vacuums of 25 inches 

 or even more, because they are sufficiently strong to withstand such strains. 



Several glass jars of strawberries and other fruits were vacuum sealed at 25 

 inches and frozen with good results. In fact, glass jars of frozen fruits make a 

 very attractive appearance. Care must be taken in paciking glass jars that suffi- 

 cient headspace is allowed to compensate for the expansion due to freezing. 

 .Vbout one-half inch is sufficient for pint or quart glass jars. 



